Acanthaceae
Creators: name: Manzitto-Tripp, Erin A.
name: Darbyshire, Iain
name: Daniel, Lucinda A. McDade Thomas F.
name: Kiel, Carrie A.
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Plantae
Tracheophyta
Magnoliopsida
Lamiales
Acanthaceae

description: Key to the genera of Acanthaceae in Africa, Madagascar, the Mediterranean region, and the Arabian Peninsula
Mangrove trees or shrubs with pneumatophores present; fruit a leathery 1-seeded capsule .............................................. Avicennia
Herbs, shrubs, woody twiners or small trees, not mangrove trees, without pneumatophores; fruit an explosively dehiscent capsule, not leathery, with (1) 2 or more seeds, or a 1–2-seeded drupe .... 2
Seeds not borne on hook-shaped retinacula, retinacula lacking or papilliform; plants without cystoliths; anthers bithecous............. 3
Seeds borne on prominent hook-shaped retinacula; plants with or without cystoliths, if cystoliths absent then anthers monothecous [8] .............................................................................................. 11
Herbs or shrubs, not twining; paired bracteoles present or absent but not large and conspicuous; flowers usually alternate or spirally arranged in few- to many-flowered inflorescences; calyx deeply 4- or 5-lobed; fruit a many-seeded (usually>10 seeds), capsule, not woody .......................................................................................... 4
Herbaceous twiners or lianas, less frequently free-standing shrubs or herbs; flowers solitary or in fascicles or racemes of opposite flowers, not spirally arranged; flowers subtended by conspicuous clasping or partially connate paired bracteoles; calyx a subentire or undulate rim or with irregular teeth, or obscurely 5-lobed; fruit either a 1–2-seeded drupe or a 2–4-seeded woody capsule ......... 8
Peduncles bearing alternate clasping scale-like sterile bracts; all bracts sclerophyllous; leaves held in rosettes or whorls ................ ......................................................................................... Elytraria
Peduncles (if present) without clasping scale-like bracts; bracts membranous or foliaceous; leaves opposite, at least some pairs dispersed along the stems................................................................. 5
Bracteoles absent; inflorescence of dense ± cylindrical spikes with imbricate bracts; calyx 4-lobed, the anterior lobe with bifid apex (rarely more deeply divided into 5 lobes); stamens 2, staminodes absent............................................................................... Nelsonia
5 Bracteoles present; inflorescence variable but if spikes cylindrical then not so dense; calyx 5-lobed; stamens 4, adaxial staminode often also present (rarely reduced to 2 stamens + 2–3 staminodes) ................................................................................................... 6
6 Pairs of bracteoles inserted below receptacle, not adnate (leaves not ternate; corollas <3 cm long); lateral 2 lobes of calyx can be somewhat shorter than other lobes but not markedly so and not hidden by the bracteoles; W and C Africa ........................ Staurogyne
6 Pairs of bracteoles partially adnate to receptacle and sometimes base of calyx (or if bracteoles sometimes free in Anisosepalum lewallei, then leaves mostly ternate and corollas 3–4 cm long); lateral 2 calyx lobes markedly shorter than other lobes and largely hidden by the bracteoles .............................................................. 7
7 Plants delicate trailing herbs; petiole usually longer than leaf blade; anther thecae with a basal appendage, this often forked; corolla widened almost from the base into a campanulate throat, palate of lower lip not bullate, i.e., without raised bosses; Gabon to Tanzania, Madagascar .......................................... Saintpauliopsis
7 Plants erect or procumbent herbs or subshrubs; petiole usually shorter than leaf blade; anther thecae with basal appendages absent or short, apiculate, not forked; corolla with a cylindrical basal tube, and ± gradually widened throat, not appearing campanulate, palate of lower lip bullate, i.e., with raised bosses; C and E Africa...................................................................... Anisosepalum
8 Fruit a fleshy drupe with 1 or 2 seeds.......................................... 9
8 Fruit a 2–4-seeded woody capsule............................................. 10
9 Drupe with 2 seeds, large (3–10 cm in diam.); leaves with a characteristic ± long narrow basal portion above an abruptly rounded or cordate base, can appear as a winged petiole; Congo Rep., D.R. Congo ........................................................... Anomacanthus
9 Drupe with a single seed, not so large; leaves without base as above; widespread........................................................ Mendoncia
10 Anthers opening by apical pores; seed with a scar on proximal face; indumentum stellate, bracteoles with a dense orange, red or mustard-yellow stellate indumentum covering external surface..... ..................................................................................... Pseudocalyx
10 Anthers opening by longitudinal slits; seed hollowed on proximal face; indumentum usually not stellate, bracteoles without a very dense orange, red or mustard-yellow indumentum externally ....... .................................................................................... Thunbergia
11 Stamens 4, sometimes with an additional staminode ................ 12
11 Stamens 2, with or without additional staminodes .................... 61
12 Anthers all monothecous; plants without cystoliths .................. 13
12 Either anthers all bithecous or 2 anthers bithecous and 2 anthers monothecous; plants with cystoliths.......................................... 21
13 Calyx long-tubular, cylindrical to inflated, with short lobes; capsule with more than 4 seeds; corolla aestivation left-contort; W and C Africa ........................................................... Physacanthus
13 Calyx not markedly tubular, deeply divided into 4 or 5 lobes; capsule with up to 4 seeds; corolla aestivation not contorted.... 14
14 Corolla lobes not comprising a single lip, either regularly 5-lobed or bilabiate; corolla not yellow........................ Stenandriopsis [4]
14 Corolla limb comprising a single lip, entire or 3- or 5-lobed, held either ventrally or dorsally, or at least with the sinus between the 2 uppermost (or outermost) lobes at a markedly wider angle than that of the other lobe sinuses, if only weakly so then corolla yellow (Crossandra flava)..................................................................... 15
15 Corolla tube twisted through 180°, the single corolla lip held dorsally, entire or 3-lobed; Tanzania ............................. Streptosiphon
15 Corolla tube not twisted, corolla lip held ventrally, 3- or 5-lobed or sometimes only undulate ........................................................... 16
16 Stamens included in corolla tube, subsessile, not inserted on a thickened flange ........................................................................ 17
16 Stamens exserted from the corolla tube, with flattened bone-like filaments, inserted on a thickened flange .................................. 18
17 Calyx 4-lobed, anterior lobe bifid; bracts not imbricate, smaller than bracteoles, these conspicuous, elliptic or obovate, diverging widely from inflorescence axis; corolla tube not narrowly cylindrical, limb obscurely 5-lobed or erose; Liberia to Tanzania ............. ................................................................................ Crossandrella
17 Calyx 5-lobed; bracts usually imbricate, larger than and enclosing bracteoles, these linear to lanceolate, not diverging widely from inflorescence axis; corolla tube narrowly cylindrical, limb 5-lobed; widespread.................................................................. Crossandra
18 Calyx 5-lobed; seeds sculptured with pectinate scales or concentric rings; bracts, bracteoles and calyx lobes glumaceous............. .................................................................................. Sclerochiton
18 Calyx 4-lobed; seeds covered in hygroscopic trichomes, puberulous or glabrous, without scales or concentric rings; bracts, bracteoles and calyces rarely glumaceous ........................................... 19
19 Anterior pair of staminal filaments each with an obtuse or acute tooth-like appendage towards the apex ventrally........... Blepharis
19 Anterior staminal filaments lacking appendages....................... 20
20 Seeds glabrous or sericeous-puberulous; stigma bilobed; bracts terminating in a single spine; plants often robust, ± tall perennial herbs, shrubs or treelets; widespread.............................. Acanthus
20 Seeds covered in long hygroscopic trichomes; stigma 1-lobed; bracts terminating in 3–5 simple or compound spines; plants often compact shrublets or acaulescent perennial herbs, if taller then slender; Namibia, western South Africa .................... Acanthopsis
21 Longer 2 stamens bithecous, shorter 2 stamens monothecous but sometimes with vestigial second theca, or if rarely (in few Neuracanthus) all stamens bithecous then shorter pair with anthers almost sessile and corolla with short tube and funnel-shaped limb comprising equal anterior and lateral lobes and partially to almost completely fused dorsal pair of lobes ........................................ 22
21 All stamens bithecous, filaments present; corolla not as above .... ................................................................................................... 24
22 Calyx bilabiate, with a 2-lobed or -toothed anterior lip and a 3-lobed or -toothed posterior lip; corolla with a funnel-shaped limb comprising equal anterior and lateral lobes and partially (or almost completely) fused dorsal pair of lobes, not bilabiate ..................... ................................................................................ Neuracanthus
22 Calyx 5-lobed, lobes either equal or with posterior lobe widest (2 + 2 + 1 configuration); corolla bilabiate ............................... 23
23 Bracts obovate with rounded apex, often with conspicuous darker pinnate-anastomosing venation; calyx ± equally 5-lobed, markedly shorter than bracteoles; small trailing herbs of rainforest; Nigeria, Bioko, Cameroon .......................................... Afrofittonia
23 Bracts variously shaped but apex acute to acuminate, 3- to palmately veined or venation inconspicuous; calyx unequally 5- lobed, posterior lobe clearly broadest (2 + 2 + 1 configuration), not or only slightly shorter than bracteoles; habit and habitat various but often in drier habitats; widespread............... Lepidagathis
24 Calyx 4-lobed, anterior lobe entire or bifid for less than half its length; anterior and posterior lobes typically much broader than lateral lobes and often enclosing them; corolla variously arranged, lobes subregular or in a 4 + 1 or 2 + 3 (rarely 1 + 3) configuration, without a hooded upper lip; filaments of anterior (long) pair of stamens?always twisted and crossing near the base.................. Barleria
24 Calyx (3-) 5-lobed, or if anterior pair of lobes partially fused and lobes of unequal width then corolla markedly bilabiate with a ± hooded upper lip; staminal filaments not twisted and crossing near the base .............................................................................. 25
25 Stamens in 2 pairs with filaments fused at base, sometimes forming a filament curtain within the corolla tube............................ 26
25 Stamens not in 2 pairs, filaments not fused, filament curtain absent ................................................................................................... 49
26 Seeds usually tuberculate or rugose, often with a thickened and irregularly crenate or serrate margin, more rarely smooth and rounded, lacking trichomes; corolla bilabiate (sometimes weakly so), with ascending-cochlear aestivation ................................... 27
26 Seeds with hygroscopic trichomes present throughout or at least along the rim; or if (rarely) glabrous then corolla subactinomorphic; corolla with left-contort aestivation .................................. 29
27 Flowers solitary in leaf axils; Botswana, South Africa .................. .................................................................................. Glossochilus
27 Flowers held in well-developed spikes or racemes, sometimes compounded into panicles ......................................................... 28
28 Anthers with thecae offset, rounded at the base; inflorescence a slender racemose thyrse with opposite cymose units; west-central Africa........................................................................... Filetia [26]
28 Anthers with thecae held at an equal or subequal height, usually basally spurred or apiculate; inflorescence often a secund spike or raceme, more rarely with opposite cymose units; widespread..... .................................................................................... Asystasia [27]
29 All anther thecae ± rounded at base, lacking basal appendages .... ................................................................................................... 30
29 One or both thecae of at least 2 of the 4 anthers with basal appendages ................................................................................ 42
30 Calyx large, inflated, fused nearly to the apex with only short lobes; all plant surfaces covered in large, prominent scale-like glands; Guinea, NE Africa ....................................... Satanocrater
30 Calyx not large and inflated, not fused nearly to the apex; plant surfaces with or without glands but not covered in dense scale-like glands.............................................................................................31
31 Corolla 1-lipped, with all 5 lobes comprising the lower lip (or rarely lip held in upper position due to floral resupination resulting from twisting of the tube) ........................................ Eremomastax
31 Corolla not 1-lipped................................................................... 32
32 Calyx with 3 posterior lobes fused for half their length or more, 2 anterior lobes free to the receptacle (2 + 3 configuration); Guineo-Congolian forests.......................................................... 33
32 Calyx without 3 posterior lobes conspicuously fused ............... 34
33 Pollen coarsely reticulate; corolla tube cylindrical, only narrowly widened towards mouth, geniculate; W and C Africa ................... ............................................................. Ruellia [Endosiphon] [20]
33 Pollen echinate, not coarsely reticulate; corolla tube infundibuliform, not markedly geniculate; Nigeria to D.R. Congo ................. ............................................................................... Dischistocalyx
34 Calyx strongly zygomorphic, posterior lobe conspicuously broader than the other lobes, ovate, elliptic or rhombic, the other lobes linear-lanceolate to oblanceolate, the 2 anterior lobes slightly broader than the 2 lateral lobes (2 + 2 + 1 configuration), all divided ± to the receptacle..........................................................................35
34 Calyx (sub)actinomorphic or if zygomorphic then not as above; posterior lobe not markedly broader than other lobes..................36
35 Capsule with fracturing placentae; flowers held in strobilate to more lax spikes, usually dorsiventral, with flowers and fertile bracts ventrally and sterile bracts dorsally, or rarely flowers solitary and axillary; pollen prolate, 12(+)-pseudocolpate, exine finely reticulate; widespread ..................................................... Phaulopsis
35 Capsule without fracturing placentae; inflorescences simple or compound dichasia, not strobilate or dorsiventral; pollen spherical, lacking pseudocolpi, exine coarsely reticulate; Angola, Namibia ................................................................... Dinteracanthus [28]
36 Capsule 2-seeded....................................................................... 37
36 Capsule 4- to many-seeded........................................................ 38
37 Calyx divided almost to the receptacle into 5 subequal (posterior sometimes longer) lobes; corolla with flattened, apically rounded, uni- or bicellular trichomes lining inner surface, tube usually ± markedly curved; stigma with 1 linear lobe, second lobe reduced to a short tooth; plants without a creosote-like smell; widespread ............................................................................... Acanthopale
37 Calyx with fused basal portion and zygomorphic limb due to partial fusion of anterior pair of lobes; corolla without such trichomes internally, tube straight; stigma bilobed; plants usually strongly odiferous with a creosote-like smell; E and S Africa, Arabia ......................................................................... Duosperma
38 Calyx lobes fused for at least 1/3 of their length and usually over half their length, with marginal hyaline regions, lobes linear(-lanceolate); capsule 4-seeded; stigma lobe with flat straight margin; pollen prolate with 12+ pseudocolpi and with sexine lips around the short apertures ...................................................... Dyschoriste
38 If calyx fused for over 1/3 of their length and with linear lobes and capsule 4-seeded (some Ruellia in Madagascar), then calyx lacking hyaline margins, stigma lobe with involute irregular margin and pollen spheroid, coarsely reticulate, lacking pseudocolpi and sexine lips .................................................................................. 39
39 Corolla typically strongly bilabiate with 2-lobed hooded upper lip and 3-lobed lower lip often with conspicuous “herring-bone” patterning, or if corolla only weakly bilabiate then less than 1 cm long; plants of (seasonal) wetlands.............................. Hygrophila
39 Corolla subactinomorphic or if zygomorphic then not strongly bilabiate with hooded 2-lobed upper lip, lacking or with only faint “herring-bone” patterning on lower lip; corolla usually> 1 cm long; plants not of wetlands....................................................... 40
40 Pollen spherical, exine coarsely reticulate or rarely (in our region only known in Ruellia togoensis) with large verrucae, lacking pseudocolpi or sexine lips; flowers usually axillary, solitary or in fascicles, more rarely in lax axillary dichasia or (in R. dissidens only) a slender terminal spike............................................ Ruellia
40 Pollen prolate, 3-porate and 12-pseudocolpate, pores flanked by sexine lips; flowers held in a terminal thyrse or panicle............ 41
41 Corolla limb either zygomorphic, with 1 lobe splitting from the tube earlier than and considerably longer than the other 4 lobes, or if subactinomorphic then lobes narrowly oblong with rounded apices and staminal filaments puberulous; Tanzania ...... ................................................ Mimulopsis [Epiclastopelma] [29]
41 Corolla limb subactinomorphic, lobes elliptic or oblong with emarginate apices; staminal filaments glabrous; Guinea to Ivory Coast, São Tomé ................................................................. Heteradelphia
42 Flowers subtended by a pair of conspicuous, ± large bracteoles, these papery to leathery and often with conspicuous reticulate venation, enclosing the calyx and base of the corolla; southern Africa............................................................................ Petalidium
42 Flowers not subtended by a pair of conspicuous bracteoles ...... 43
43 Capsules with fracturing placentae; calyx strongly zygomorphic, posterior lobe ovate or elliptic, markedly broader than other lobes, these linear-lanceolate to oblanceolate (2 + 2 + 1 configuration); inflorescences often dorsiventral spikes, with flowers and fertile bracts ventrally and differently shaped sterile bracts dorsally, rarely radially symmetrical .................................................... Phaulopsis
43 Capsules without fracturing placentae or with placentae easily dislodged but lateral walls of capsule not tearing; calyx actinomorphic or only weakly zygomorphic, posterior lobe not markedly broader than other lobes; inflorescences not dorsiventral spikes........ 44
44 Corolla limb subactinomorphic, throat lacking “herring-bone” patterning; plants with trailing or procumbent stolons from a woody rootstock sometimes rooting adventitiously, with clusters of leaves or short erect leafy stems along the stolons, leaves linear to narrowly elliptic or obovate, plant often with a “grass-like” gestalt; southern Africa ............................................................ Ruelliopsis
44 Corolla limb zygomorphic or weakly so, throat often with prominent “herring-bone” patterning; plant habit not as above, not grass-like ................................................................................... 45
45 Calyx lobes fused for at least 1/3 of their length and usually over half their length, with hyaline margins between the lobes, lobes linear(-lanceolate); ovary with 2 ovules per locule, capsule 4-seeded...................................................................... Dyschoriste
45 Calyx lobes divided to the receptacle or shortly fused, lacking hyaline margins; lobes linear or often spathulate; ovary with 2–8 ovules per locule; capsule often either>4-seeded or 2-seeded...... 46
46 Outermost theca of each of longer pair of stamens with a conspicuous curved appendage, other thecae with much shorter appendages or rounded .......................................................... Mimulopsis
46 Either all thecae or 1 of each pair of thecae of all anthers with an appendage.................................................................................. 47
47 Leaves conspicuously dentate or crenate; capsule with>4 and usually ≥8 seeds; seeds with hygroscopic trichomes largely restricted to the rim, surfaces with or without short non-hygroscopic trichomes; E and S Africa ............................................. Mellera [24]
47 Leaves entire or with a single tooth on each side; capsule usually 2-seeded, hygroscopic trichomes covering entire seed surface....48
48 Corolla bilabiate, 10–12.5 mm long, tube cylindrical, without a clearly expanded throat; lower lip with long bristly trichomes internally; pollen with 12 pseudocolpi; SW Angola .............. Mcdadea
48 Corolla subactinomorphic, not strongly bilabiate, 22–45 mm long, tube clearly differentiated into a narrow basal tube and an expanded throat; pollen with 18+ pseudocolpi; Angola to D.R. Congo and Zimbabwe ..................................................... Strobilanthopsis
49 Seeds (where known) sculptured with concentric rings at least towards the rim, lacking trichomes; corolla with left-contort aestivation..... 50
49 Seeds not sculptured with concentric rings, either covered in trichomes or, if glabrous, then surface smooth; corolla with quincuncial aestivation ........................................................................... 55
50 Flowers held in well-developed racemes or spikes, sometimes branched to form panicles; continental Africa and Madagascar ............. 51
50 Flowers held in axillary or subterminal fascicles, glomerules or short umbels; Madagascar [13] ................................................. 52
51 Inflorescence units 1-flowered; calyx ≥ 9 mm long, usually extending beyond or subequal in length to bracteoles, often showy and colored similar to corolla; widespread in tropical continental Africa........................................................................... Whitfieldia
51 Inflorescence units 1- or 2–3-flowered; calyx short, up to 8 mm long, hidden within paired bracteoles, not colored similar to corolla; Kenya, Tanzania, Madagascar ................ Chlamydacanthus
52 Peduncle of inflorescence units conspicuous, filiform, 7–14 mm long, considerably longer than bracteoles and calyces .................. .................................................................................... Zygoruellia
52 Inflorescence units either sessile or peduncles shorter than or equal in length to bracteoles and calyces, not filiform........................ 53
53 Corolla bright orange-red or scarlet, tube markedly curved; stamens exserted well beyond corolla lobes .................... Camarotea
53 Corolla variously colored but not bright orange-red or scarlet, tube straight or curved; stamens not or barely exserted beyond corolla lobes .......................................................................................... 54
54 Corolla tube subequal in length to limb, limb strongly bilabiate, lobes of upper lip partially fused, all lobes with long wispy white trichomes internally ............................................. Leandriella [14]
54 Corolla tube longer than limb, often markedly so, limb not so strongly bilabiate, lobes of upper lip more deeply divided, or limb subactinomorphic, all lobes lacking long white trichomes internally .................................................................. Forcipella / Vindasia [15]
55 Longer pair of stamens exserted from corolla tube or clearly visible at corolla mouth; stigma capitate-bilobed; corolla strongly bilabiate with 2 posterior lobes largely or completely fused to form a hooded upper lip....................................................... Lepidagathis
55 Stamens included within corolla tube; stigma flattened, fan-shaped or rhombic; corolla not so strongly bilabiate, posterior pair of lobes fused somewhat higher than other lobes but not forming a hooded upper lip..................................................................................... 56
56 Flowers held in ± spherical heads surrounded by several whorls of bracts, outermost bracts with a spiny or bristly margin and/or long, ≥ 20 mm long; E and S Africa.......................................... Crabbea
56 Flowers arranged in smaller, non-spheroidal heads or in spikes, glomerules or panicles; bracts not spiny, smaller; Madagascar [7] ................................................................................................... 57
57 Inflorescences pedunculate axillary heads, spikes, umbels or dichasial panicles, or if fasciculate then inflorescence units held within paired clasping bracts ..................................................... 58
57 Inflorescences sessile axillary glomerules, inflorescence units not held within paired clasping bracts ............................................. 60
58 Flowers subtended by a whorl of (3) 4 bracts connate for at least half their length to form a 3–4-lobed epicalyx; corolla 37–50 mm long................................................................................. Boutonia
58 Flowers or inflorescence units subtended by a pair of bracts; bracts not connate or only basally so; corolla up to 25 mm long ............................................................................................. 59
59 Inflorescences of spikes, dichasial panicles or heads; bracts subtending each inflorescence unit paired but the pairs often unequal, not adpressed, variously shaped ................................. Podorungia
59 Inflorescences of umbels (sometimes fasciculate) or lax dichasia; bracts subtending each inflorescence unit paired, subequal, adpressed, ovate or elliptic ..................................... Pseudodicliptera
60 All bracts of glomerules linear or lanceolate, without recurved apices; plants often with dense pale indumentum on stems and/or abaxial surface of leaves................................................. Lasiocladus
60 Outermost bracts of glomerules broader, foliaceous, sometimes with recurved apices; plants without dense pale indumentum ...... ..................................................................................... Pericalypta
61 Anthers monothecous ................................................................ 62
61 Anthers bithecous ...................................................................... 67
62 Corolla resupinate through ±180° twist in corolla tube; flowers held between paired clasping or partially fused ± conspicuous bracts ............................................................................. Hypoestes
62 Corolla not resupinate, tube not twisted; pairs of bracts neither clasping nor partially fused ....................................................... 63
63 Corolla either subregularly 5-lobed or if bilabiate then upper lip conspicuously 2-lobed and lower lip deeply divided into 3 lobes; staminodes 2, sometimes basally fused to filaments of fertile stamens; seeds either smooth on both faces, or smooth on outer face and irregularly ridged on inner face, this with or without a raised rim.........64
63 Corolla strongly bilabiate, upper lip undivided or at most shortly notched, lower lip only partially divided into 3 lobes or almost undivided; staminodes absent; seeds tuberculate, rugulose or with concentric ridges, without a raised rim...................................... 66
64 Corolla tube much longer than limb, markedly curved and gradually expanded towards mouth; Socotra .......................... Ballochia
64 Corolla tube either shorter than limb or if longer than limb then narrowly cylindrical throughout except for slight expansion at the mouth; not on Socotra ......................................................... 65
65 Corolla tube narrowly cylindrical, longer than limb; limb either subequally 5-lobed or bilabiate with posterior 2 lobes partially fused, anterior 3 corolla lobes not reflexed or widely divergent.... ................................................................................. Ruspolia [30]
65 Corolla tube more broadly cylindrical or saccate, shorter than or subequal to limb; posterior pair of lobes partially fused and erect, anterior 3 corolla lobes either reflexed and held against the tube, or widely divergent............................................................. Ruttya
66 Corolla with tube up to 10 mm long, upper lip lanceolate, hooded, largely enclosing the staminal filaments (flower nototribic); C and E Africa ........................................................... Monothecium [31]
66 Corolla with tube longer than 10 mm or, if shorter, then upper lip subulate, oblong-lanceolate or elliptic, not hooded, often recurved or inrolled, stamens held between the 2 lips (flower pleurotribic); widespread......................................................... Brachystephanus
67 Staminodes present, sometimes basally fused to the adjacent staminal filament............................................................................... 68
67 Staminodes absent ..................................................................... 81
68 Calyx 4-lobed, anterior lobe entire or bifid for less than half its length; anterior and posterior lobes typically much broader than lateral lobes and often enclosing them; corolla arrangement variable, lobes subregular or in a 4 + 1 or 2 + 3 configuration, without hooded upper lip; staminal filaments?always twisted and crossing near the base ..................................................................... Barleria
68 Calyx 5-lobed or equally 4-lobed, or if anterior pair of lobes partially fused (less than half their length) and lobes of unequal width then corolla markedly bilabiate with ± hooded upper lip; staminal filaments not twisted and crossing near the base ...................... 69
69 Pollen bipororate, circular in apertural view, with a broad marginal girdle-like ring of sexine; flowers held in axillary and subterminal glomerules on largely leafless woody stems; corolla with dense tuft of yellow trichomes on palate of lower lip immediately proximal to the lobes; Madagascar ............................................... Ritonia [32]
69 Pollen and macromorphological characters not in the above combination............................................................................... 70
70 Seeds with hygroscopic trichomes present throughout or at least around the rim; corolla either with left-contort or quincuncial aestivation.................................................................................. 71
70 Seeds without hygroscopic trichomes, sculptured with tuberculae, echinae or verruculae, or smooth; corolla with ascending-cochlear aestivation.................................................................................. 78
71 Corolla salverform, with narrowly cylindrical tube markedly longer than spreading 5-lobed limb; limb subactinomorphic or with sinus between 2 adaxial lobes wider than the other sinuses ................ 72
71 Corolla not salverform, often markedly bilabiate or, if limb subactinomorphic, then tube not long and narrowly cylindrical...... ............................................................................................. 73
72 Corolla blue or violet; flowers held in (1)2(3)-flowered dichasia in the axils of leaves, each flower subtended by a pair of conspicuous ovate foliaceous bracteoles held on a winged pedicel; Cameroon, Central African Republic, D.R. Congo ................... Kosmosiphon
72 Corolla yellow, orange or white; flowers held in terminal spikes or dense thyrses, often with conspicuous imbricate bracts, or bracts linear; bracteoles linear; winged pedicels absent; widespread....... .................................................................................... Lankesteria
73 Filament curtain absent; corolla aestivation quincuncial ........... 74
73 Filament curtain present; corolla aestivation left-contort .......... 75
74 Inflorescences dense secund spikes with unequal fertile and sterile bracts; calyx lobes markedly unequal in 2 + 2 + 1 configuration, posterior lobe broadest, ovate or elliptic; seeds with long hygroscopic trichomes; Madagascar [33]............................................ Lepidagathis
74 Inflorescences dense terminal thyrses, not secund, pairs of bracts equal; calyx of 5 subregular linear lobes; seeds with minute trichomes only; D.R. Congo ...................................... Schaueriopsis
75 Capsule 2-seeded; 2 anterior calyx lobes fused more distally than 3 posterior lobes, inflorescences not subtended by spines................ .................................................................................... Duosperma
75 Capsule 4- to ca. 30-seeded; anterior calyx lobes not fused more distally than posterior lobes or, if so, then fascicles of flowers subtended by hard spines ................................................................ 76
76 Leaf base decurrent onto petiole, forming a ± marked wing; corolla strongly bilabiate with laterally compressed and curved hooded upper lip and basally hinged lower lip........................... Brillantaisia
76 Leaf base not winged; corolla not so strongly bilabiate, upper lip may be hooded but not laterally compressed nor so strongly curved, lower lip not basally hinged ............................................... 77
77 Capsule 4-seeded; lower corolla lip lacking stiff retrorse bristles; anther thecae usually spurred; plants usually of dry habitats ........ .................................................................................... Dyschoriste
77 Capsule 8–20+-seeded; lower lip of corolla with numerous stiff retrorse bristles; anther thecae not spurred; plants of (seasonal) wetlands....................................................................... Hygrophila
78 Inflorescence of curved secund spikes, with the flowers held upright, 1 flower per inflorescence node; corolla tube markedly infundibuliform, with basal cylindrical portion and abruptly widened throat; South Africa, Eswatini ................................ Mackaya
78 Inflorescences of axillary solitary flowers or fascicles, or of slender spikes with opposite flowers or fascicles at each inflorescence node; corolla tube cylindrical throughout or, if with an expanded throat, then throat gradually widened ........................................ 79
79 Corolla tube curved and gradually widened distally, 7–10 mm in diam. at mouth; dorsal pair of corolla lobes largely fused to form hooded upper lip; Nigeria, Bioko, Cameroon ...... Graptophyllum
79 Corolla tube cylindrical to narrowly so or at most narrowly campanulate, up to 3 mm in diam. at mouth, straight or ± abruptly bent distally; dorsal pair of corolla lobes not largely fused, upper lip not hooded ....................................................................................... 80
80 Inflorescences long slender spikes; corolla tube usually much longer than limb, rarely shorter than limb; widespread ...................... ......................................................................... Pseuderanthemum
80 Inflorescence axillary (but branches can be largely leafless at flowering), flowers solitary or in fascicles; corolla tube shorter than limb; Madagascar ..................................................... Oplonia [34]
81 Corolla resupinate through ±180° twist in corolla tube............. 82
81 Corolla not resupinate or if so, then due to twisting of pedicel, corolla tube not twisted ................................................................. 84
82 Thecae of each anther widely separated by extension of the connective tissue; Madagascar ......................................... Vavara [35]
82 Anther thecae immediately superposed or slightly overlapping .... ................................................................................................... 83
83 Capsule with fracturing placentae, placenta base and thin walls tearing away from thickened flanks ............................... Dicliptera
83 Capsule without fracturing placentae, walls and placenta base remaining attached at dehiscence ........................ [Peristrophe] [36]
84 Corolla strongly bilabiate with lips markedly longer than tube (often 2× longer or more), upper lip strongly hooded, straight to gradually curved, lower lip narrowly oblong, strap-shaped or narrowly cylindrical, usually recoiled at anthesis ..................................... 85
84 Corolla limb various, if bilabiate, then lips usually not markedly longer than tube or if so then lower lip broader and not recoiled at anthesis .................................................................................. 87
85 Pollen bipororate, circular in apertural view, with a broad marginal girdle-like ring of sexine (“gürtelpollen”); inflorescence spikes slender with rachis sometimes visible between the pairs of bracts; Madagascar .............................................. Anisotes perplexus [37]
85 Pollen 2-, 3- or 4-colporate with pseudocolpi flanking each aperture, prolate, without a marginal girdle; inflorescences variable but if spikes then more contracted with usually imbricate bracts, not so slender.......................................................................................86
86 Capsule with fracturing placentae; Nigeria, E and S Africa .......... ............................................................................ Metarungia [38]
86 Capsule without fracturing placentae; widespread .......... Anisotes
87 Flowers sternotribic; trailing or procumbent herb with axillary fascicles of flowers; bracts, bracteoles and calyx lobes with palehyaline margins; Kenya .......................................... Kenyacanthus
87 Plants without the above combination of characters.................. 88
88 Pollen bipororate, circular in apertural view, with a broad marginal girdle-like ring of sexine (“gürtelpollen”); corolla bilabiate; anthers with thecae either held at an equal height and parallel or offset to fully superposed and/or oblique, basally muticous, if offset then the upper theca slightly longer than the lower theca ..................... ................. Isoglossa / Melittacanthus / Sphacanthus / Celerina [39]
88 Pollen variable but not as above; if anther thecae offset to superposed then often with a basal appendage on the lower theca or both thecae, and the upper theca slightly shorter than the lower theca ............................................................................................. 89
89 Anther thecae each with a broad flattened appendage with irregular projections along the rim (resembling a “chicken’ s crest”); corolla intricately speckled or striped, lacking a rugula; Nigeria, Bioko, Cameroon, Gabon ................................................... Champluviera
89 Anther thecae either without appendages or if appendages present then not as above, appendages apiculate to well-developed and elongate, often curved, sometimes with a bifid apex but without projections along the rim; corolla coloring various; if anther appendages present, then corolla with a rugula............................. 90
90 Corolla lacking a rugula; anther thecae held at an equal height (but sometimes unequal in size) and parallel or sagittate; anther appendages absent......................................................................... 91
90 Corolla with a rugula present on upper lip and dorsal side of tube; anther thecae usually strongly offset to fully superposed and/or oblique; lower theca or both thecae often with a well-developed appendage................................................................................ 101
91 Corolla 9–12 mm long, with narrowly cylindrical tube longer than the limb; corolla lobes all reflexed at anthesis; anther thecae held at ± equal height but 1 theca larger than the other; pollen 6-colporate, sculptured with verruculae arranged in ± well-defined longitudinal lines; W and C Africa.......................................... Chlamydocardia
91 If corolla with narrowly cylindrical tube then considerably longer than 12 mm; corolla lobes not all reflexed at anthesis but apices can be recurved or recoiled; anther thecae not unequal in size; pollen not as above ......................................................................... 92
92 Upper lip of corolla curved and laterally compressed, very narrow; lower lip lacking raised “herring-bone” pattern; seeds covered in glochidiate tubercles; D.R. Congo, Kenya, Mozambique ............. ................................................................................... Cephalophis
92 Plant not with the above combination of characters; if upper lip of corolla curved and laterally compressed then lower lip with conspicuous raised “herring-bone” pattern and seeds not covered in glochidiate tubercles .................................................................. 93
93 Upper lip of corolla not hooded, sometimes apically recurved or recoiled; lower lip without raised “herring-bone” pattern; seeds discoid with a raised rim............................................................ 94
93 Upper lip of corolla ± hooded; lower lip often with raised “herring-bone” pattern; seeds less strongly flattened, without a marginal rim ........................................................................................... 100
94 Inflorescences pendulous; corolla ascending-sigmoid-shaped in bud, tube strongly expanded apically; lower lip shortly 3-lobed; Socotra .................................................................... Angkalanthus
94 Inflorescences erect; corolla not ascending-sigmoid-shaped in bud, tube cylindrical or only slightly widened upwards; lower lip deeply 3-lobed ........................................................................... 95
95 Upper corolla lip broadly elliptic with rounded or slightly emarginate apex; leaves lanceolate with length: width ratio 7–9: 1, longest leaves 11–15 cm long; Madagascar ....................................... .............................................................................. Dolichostachys
95 Upper corolla lip linear-lanceolate to narrowly elliptic, apex acute or notched; leaves variable, if narrow then less than 10 cm long ............................................................................................. 96
96 Corolla tube narrowly cylindrical, barely widened at mouth, often longer than lobes; upper lip markedly smaller than lower lip; stamens held close to upper lip of corolla with short filaments (flower nototribic), anthers parallel to filament .................. Ecbolium [40]
96 Corolla tube cylindrical to somewhat campanulate but not narrowly cylindrical, shorter than or subequal in length to lobes; upper lip ± equal in length to lower lip; stamens held ± equidistant between the upper and lower lips (flower pleurotribic), anthers often held perpendicular to filaments ................................................. 97
97 Corolla lobes spreading or recurved but not recoiled at anthesis; pollen 3-colporate with only weakly defined colpi and lacking pseudocolpi; E and S Africa, Arabian Peninsula........................... ............................................................................. Megalochlamys
97 Corolla lobes, at least on lower lip, becoming apically recoiled at anthesis; pollen 3–6-colporate, colpi conspicuous, pseudocolpi present ....................................................................................... 98
98 Inflorescence 4-angular with imbricate slightly concave bracts; pollen (4) 5 (6)-colporate, with pseudocolpi fused towards one or both poles to form arcs, circles or ellipses; coastal Kenya and Tanzania ...................................................................... Trichaulax
98 Inflorescence not conspicuously 4-angular, if bracts imbricate then convex; pollen 3-colporate, pseudocolpi not fused towards poles, parallel to the colpi .................................................................... 99
99 Plants from Madagascar .......................................... Populina [41]
99 Plants from Socotra, Somalia, Botswana, South Africa ................ ................................................................................. Chorisochora
100 Calyx zygomorphic (2 + 2 + 1 configuration), lobes oblong-elliptic to oblong-oblanceolate, posterior lobe broadest, 4–7 mm wide; Madagascar .................................................................. Ambongia
100 Calyx not or barely zygomorphic, lobes linear or lanceolate, less than 4 mm wide; Ethiopia, Somalia ........................ Ichthyostoma
101 Corolla tube narrowly cylindrical throughout or ventrally abruptly expanded in distal half, usually considerably longer than lips except in R. pulcher where lower lip> 20 mm long; upper lip linear-lanceolate to shortly ovate, not hooded; anthers with thecae muticous or lower theca apiculate ................. Rhinacanthus
101 Corolla tube not so narrowly cylindrical throughout nor abruptly expanded on ventral side of tube, if tube longer than lips then upper lip hooded; anthers usually with well-developed basal appendages ......................................................................... 102
102 Capsule with fracturing placentae; inflorescences strobilate secund spikes, bracts often with conspicuous and abrupt white- or pinkish hyaline margins .......................................................... 103
102 Capsule with placentae not fracturing; inflorescences variable, if strobilate, secund spikes then bracts without abrupt pale hyaline margins (margins sometimes gradually paler)......................... 104
103 Anthers dehiscing by basal pores; Nigeria, Cameroon, Equatorial Guinea, Gabon ............................................................. Ascotheca
103 Anthers dehiscing by longitudinal slits; widespread ......... Rungia
104 Capsule 2-seeded (rarely 4-seeded), seeds smooth, glabrous or white-sericeous, or with 2 tufts of moniliform trichomes ....... 105
104 Capsule usually 4-seeded, more rarely 2-seeded, seeds variously sculptured or with short trichomes, rarely smooth .................. 106
105 Inflorescences of axillary or both axillary and terminal spikes; bracts elliptic, ovate or obovate, often imbricate, inflorescence units at each axil often>1-flowered; seeds 2–3 mm in diam., lenticular with a sharp rim, ± symmetrical in cross section and lacking a prominent ridge on one side, glabrous ........... Meiosperma [42]
105 Inflorescences either axillary and 1-flowered (bracts undifferentiated from the leaves) or in well-defined, mostly terminal spikes (bracts highly modified), rarely in axillary pedunculate fascicles; bracts in species with well-defined spikes usually narrow, linear to lanceolate, or rarely (in one species) broadly elliptic to obovate; seeds variable, often larger than 3 mm in diam. with a rounded rim (including in the single species with broad bracts) and/or variously pubescent, or if small and with sharp rim then asymmetric in cross section and with a prominent ridge on one side............................ ............................................................................ Pogonospermum
106 Corolla red or orange with tube somewhat curved and gradually widened, longer than lips; anthers with both thecae appendaged; Socotra ....................................................................... Trichocalyx
106 Corolla variable but usually with ± straight tube; if corolla red and with curved, gradually widened tube, then anthers with only the lower theca appendaged .......................................................... 107
107 Inflorescences secund spikes with usually imbricate, obovate, spathulate or lanceolate bracts, these green, white or pink; seeds subglobose, with hygroscopic or papillose trichomes; mainly Madagascar, 1 sp. widespread in tropical Africa.............. Anisostachya
107 Inflorescences variable; if secund spikes with imbricate bracts then seeds not as above, primarily without (rarely with) hygroscopic or papillose trichomes; widespread................ Justicia [43]
Key to the genera of Acanthaceae in Asia and Australasia (excluding the Arabian Peninsula and Mediterranean region)
Mangrove trees or shrubs with pneumatophores present; fruit a leathery 1-seeded capsule .............................................. Avicennia
Herbs, shrubs, woody twiners, or small trees, not mangrove trees (although occasionally mangrove shrubs in Acanthus), without pneumatophores; fruit a woody or thin-walled capsule with (1) 2 or more seeds............................................................................... 2
Seeds not borne on hook-shaped retinacula, either retinacula lacking or papilliform; plants without cystoliths; all anthers bithecous ..................................................................................................... 3
Seeds borne on prominent hook-shaped retinacula; plants with or without cystoliths, if cystoliths absent then anthers monothecous.................................................................................... 7
3 Herbs or shrubs, not twining; paired bracteoles present or absent but not large and conspicuous; calyx deeply 4- or 5-lobed; fruit a many-seeded (usually>10 seeds) capsule ................................... 4
3 Herbaceous twiners or lianas, less frequently free-standing shrubs or herbs; flowers solitary or in fascicles or racemes of opposite flowers, not spirally arranged; calyx a subentire or undulate rim or with irregular teeth, or obscurely 5-lobed; fruit a 2–4-seeded capsule ......................................................................................... 6
4 Peduncles bearing spirally arranged, clasping, scale-like sterile bracts; all bracts sclerophyllous; leaves held in rosettes or basal whorls; India, Sri Lanka .................................................. Elytraria
4 Peduncles (if present) without clasping scale-like bracts; bracts membranous or foliaceous; leaves mostly opposite, at least some pairs dispersed along the stems.................................................... 5
5 Stamens 2, staminodes absent; bracteoles absent (rarely present); inflorescence of dense ± cylindrical spikes with imbricate bracts; calyx 4-lobed, the anterior lobe with bifid apex (rarely more deeply divided into 5 lobes) ........................................................ Nelsonia
5 Stamens 4, adaxial staminode often also present, or rarely reduced to 2 stamens +2–3 staminodes; bracteoles present; inflorescence variable but, if spikes cylindrical, then not so dense; calyx 5-lobed......................................................................... Staurogyne
6 Stigma ± equally 2-lobed, each lobe subdivided into 2 unequal lobes; pollen 7–9-lobate and -colpate; India .................... Meyenia
6 Stigma funnel-shaped, unequally 2-lobed or if equally so then not subdivided; pollen spiraperturate and unlobed; widespread.......... .................................................................................... Thunbergia
7 Stamens 4, sometimes with an additional staminode................... 8
7 Stamens 2, with or without additional staminodes .................... 39
8 Anthers all monothecous; plants without cystoliths; corolla 1-lipped........................................................................................ 9
8 Either anthers all bithecous or 2 anthers bithecous and 2 anthers monothecous; plants with cystoliths; arrangement of corolla lobes various but not 1-lipped ............................................................. 12
9 Stamens included in corolla tube, subsessile, not inserted on a thickened flange; India and Sri Lanka to Myanmar .............. Crossandra
9 Stamens exserted from corolla tube, with flattened bone-like filaments, inserted on a thickened flange........................................ 10
10 Anterior staminal filaments lacking appendages, if flattened then gradually narrowed towards apex; seeds glabrous or sericeous-puberulous ...................................................................... Acanthus
10 Anterior pair of staminal filaments flattened and either with an obtuse or acute tooth-like appendage or truncate to rounded towards apex ventrally; seeds with branched hygroscopic trichomes or tuberculate ................................................................................. 11
11 Leaves opposite; flowers solitary or paired in the leaf axils, each flower or pair of flowers subtended by 2 pairs of bracts, outer pair entire, inner pair trifid; ovary without apical tufts of glandular trichomes; seeds tuberculate; India ..................... Cynarospermum
11 Leaves in pseudowhorls of (3) 4; inflorescences variable but not consisting of solitary or paired flowers in leaf axils; bracts entire or toothed, not trifid; ovary with 2 apical tufts of glandular trichomes; seeds with branched hygroscopic trichomes; widespread ....................................................................................... Blepharis
12 Calyx distinctly bilabiate, with a 2-lobed or -toothed anterior lip and a 3-lobed or -toothed posterior lip; corolla with a funnel-shaped limb comprising equal anterior and lateral lobes and partially (or almost completely) fused dorsal pair of lobes; India to Laos ........................................................................ Neuracanthus
12 Calyx not distinctly bilabiate (although can appear so in Barleria), either 4- or 5-lobed, lobes can be equal or unequal in shape and size; if calyx appears bilabiate then corolla not as above .............. ................................................................................................... 13
13 Calyx 4-lobed, anterior lobe entire or bifid for less than half its length; anterior and posterior lobes typically much broader than lateral lobes and often enclosing them; corolla variously arranged, lobes subregular or in a 4 + 1 or 2 + 3 configuration, without hooded upper lip; filaments of anterior (long) pair of stamens?always twisted and crossing near the base........................................ Barleria
13 Calyx 5-lobed, or if anterior pair of lobes partially fused and lobes of unequal width then corolla strongly bilabiate with ± hooded upper lip; staminal filaments not twisted and crossing near the base.... 14
14 Seed surfaces smooth or sculptured, lacking trichomes; corolla aestivation ascending-cochlear .................................................. 15
14 Seed surfaces either covered by trichomes or with trichomes at least along margins and/or near the apices (trichomes minute in a few genera, such as Hulemacanthus, absent in Borneacanthus); corolla aestivation left-contort or quincuncial ........................... 19
15 One pair of stamens with bithecous anthers, the other pair with monothecous anthers; Thailand, Malaysia ............ Thysanostigma
15 Both pairs of stamens with bithecous anthers ........................... 16
16 Corolla strongly bilabiate with upper two lobes almost completely fused into a hooded or erect, apically notched lip; either stamens included in corolla tube or if exserted then anthers usually with thecae unevenly inserted on the filament and offset by ca. half their length ......................................................................................... 17
16 Corolla not so strongly bilabiate, 5 lobes often subequal although arranged in a 2 + 3 configuration and upper two lobes can be partially fused; stamens exserted, anther thecae held at a subequal height ......................................................................................... 18
17 Mouth of corolla closed due to raised, rounded palate of lower lip, upper lip held erect; stamens included in corolla tube, filaments very short, anthers with thecae held at a subequal height; calyx lobes apically reflexed; Borneo ................................. Linariantha
17 Mouth of corolla not closed, palate of lower lip can be raised but not so strongly bulging, upper lip hooded, not erect; stamens exserted and held within hooded upper lip, filaments well developed; calyx lobes not markedly reflexed apically; Malaysia, Sumatra, Borneo ......................................................................... Filetia [44]
18 Calyx with a ± distinct tubular portion, the tube sometimes longer than the lobes; inflorescences often with opposite cymose units, pedicels widely divergent from inflorescence axis and can be thickened; India, Malaysia .............................. Phialacanthus [45]
18 Calyx divided ± to the base; inflorescences often secund, pedicels not so widely diverging from the axis and not thickened; widespread...................................................................... Asystasia
19 Corolla lacking a filament curtain ............................................. 20
19 Corolla with a conspicuous filament curtain ............................. 27
20 One pair of stamens with bithecous anthers, the other pair with monothecous anthers ................................................................. 21
20 Both pairs of stamens with bithecous anthers ........................... 22
21 Stamens exserted beyond corolla lobes, corolla limb very short and not strongly bilabiate (although posterior pair of lobes are partially fused); inflorescence a many-flowered thyrse with flowers in dense whorls at each node, not secund; bracts and bracteoles inconspicuous; New Guinea ................................ Hulemacanthus
21 Stamens not exserted beyond corolla lobes, corolla limb strongly bilabiate; inflorescence a secund spike, spikes sometimes compounded into dense heads; bracts and bracteoles usually conspicuous; widespread ........................................................ Lepidagathis
22 Corolla bilabiate, with ± hooded upper lip; corolla aestivation quincuncial ................................................................................ 23
22 Corolla subactinomorphic or weakly zygomorphic, not strongly bilabiate with hooded upper lip; corolla aestivation left-contort.................................................................................25
23 Anther thecae conspicuously spurred at base; China to Malaysia ................................................................................. Chroesthes
23 Anther thecae not spurred at base, either obtuse or at most minutely apiculate............................................................................... 24
24 Capsule stipitate; seeds glabrous; calyx lobes all linear or linear-lanceolate; bracts and bracteoles small and inconspicuous; Borneo .............................................................................. Borneacanthus
24 Capsule not or barely stipitate; seeds with hygroscopic trichomes; calyx lobes ± markedly unequal, posterior lobe broadest, lateral lobes narrowest (2 + 2 + 1 configuration); bracts and bracteoles usually conspicuous, often similar to calyx lobes in shape and size; widespread................................................................ Lepidagathis
25 Flowers with “X-shaped anthers” (i.e., thecae extend outwardly in a 180° configuration from expanded filament connective tissue); China ........................................................................... Pararuellia
25 Anthers various but not “X-shaped” as above........................... 26
26 Plants with long-tubed, pale-colored corollas; leaves not held in a basal rosette; Papuasia......................................... Leptosiphonium
26 Corollas not long-tubed and pale-colored, typically short infundibuliform, primarily purple; leaves typically held in a basal rosette; Australia, New Caledonia, New Guinea .................... Brunoniella
27 Corolla strongly bilabiate .......................................................... 28
27 Corolla infundibuliform, campanulate or other shapes, not strongly bilabiate ....................................................................................... 29
28 Plants large herbs or weak shrubs to 2.5 m tall; capsule oblong or obovate, not with noticeably thin walls; ovules 4 or fewer per ovary; India ................................................................ Calacanthus
28 Plants herbaceous, typically <1 m tall (very rarely to 1.5 m tall); capsule cylindrical, with noticeably thin walls; ovules>8 per ovary, capsule typically polyspermous (≥16 seeds); widespread ................ ......................................................................................... Hygrophila
29 Capsule with fracturing placentae ............................................. 30
29 Capsules with non-fracturing placentae..................................... 31
30 Inflorescences complex, densely bracteate and compact, with numerous, small flowers; flowers not subtended by large, conspicuous, paired leaf-like bracts; corolla small (<10 mm long); anther thecae without appendages; widespread...................... Phaulopsis
30 Inflorescences axillary, solitary or in simple dichasia, not complex and dense as above; flowers subtended by a large, conspicuous, pair of leaf-like bracts; corolla> 34 mm long; anther thecae with appendages; India and Nepal ........................................ Petalidium
31 Anthers with at least some thecae with basal appendages......... 32
31 Anthers lacking basal appendages............................................. 36
32 Deciduous tree to 5 m tall, flowering before the leaves appear; ultimate branches numerous and curved-ascending; karst hills of Laos ................................................................... Xylacanthus [25]
32 Herbs or shrubs, habit not as above........................................... 33
33 Leaf pairs strongly and consistently anisophyllous, the smaller leaf about 1/3 of the size of the larger; each anther theca with a pair of appendages; Thailand ............................................. Diceratotheca
33 Leaf pairs sometimes slightly dissimilar in size but not strongly (nor consistently) anisophyllous; anther thecae variously appendaged but not with 2 appendages per theca............................... 34
34 Inflorescences of very long, terminal spikes, these commonly 30 cm in length; Malaysia ........................................ Stenothyrsus
34 Inflorescences variable, primarily of racemes, less commonly of spikes or solitary flowers, if spikes, consistently <15 cm long .....35
35 Ovary with 8 ovules; India, China ........................ Echinacanthus
35 Ovary with 4 ovules (occasionally fewer); widespread .............. .............................................................................. Dyschoriste
36 Ovary with 16 ovules........................................ Strobilanthes [46]
36 Ovary primarily with fewer than 16 ovules (with rare exceptions) ................................................................................................... 37
37 Corolla resupinate via twisting of the tube through 180°; inflorescences thyrsoid with secondary flowers in the axils of bracteoles; corolla with a ventricose throat......................... Strobilanthes [47]
37 Corolla usually not resupinate via twisting of the tube (except in Strobilanthes dyeriana, S. autapomorpha, and S. steenisiana), but corolla distortions sometimes achieved by bending of the corolla throat; if resupinate, then not in combination with above additional features...........................................................................................38
38 Corolla internally with prominent rows of trichomes along posterior surface, these functioning to retain the style (very rarely secondarily lost); corolla typically with thin but prominent ridge between pairs of stamens, representing vestigial staminode.......... ................................................................................. Strobilanthes
38 Corolla internally lacking prominent rows of trichomes along posterior surface; corolla lacking a ridge between pairs of stamens........................................................................... Ruellia
39 Anthers monothecous ................................................................ 40
39 Anthers bithecous (one theca sometimes reduced in size) ........ 43
40 Corolla tube twisted through 180°, limb resupinate with the 3-lobed lower lip held in the upper position and unlobed or emarginate upper lip held in the lower position; India to China and Thailand ......................................................................... Hypoestes
40 Corolla tube not twisted; if flower resupinate then this achieved through geniculation of corolla tube.......................................... 41
41 Corolla 30–60 mm long, bright red-orange; clambering shrubs; China to Indonesia ................................................... Clinacanthus
41 Corolla up to 10 mm long, white or pale blue, with or without red or mauve markings; perennial herbs or small shrubs, not clambering ................................................................................. 42
42 Corolla with 4-lobed upper lip and unlobed lower lip; each anther with theca terminal and transverse, sometimes also with a vestigial second theca observed as a bump below the fertile theca; flowers axillary and solitary, held on lateral branches; Australia ............... ....................................................................... Xerothamnella [48]
42 Corolla with shortly bilobed, hooded upper lip and 3-lobed lower lip; each anther with theca dorsifixed and ± parallel to filament, without a vestigial second theca; inflorescence a small, dense secund spike; India, Sri Lanka ................................... Monothecium
43 Staminal filament divided at apex, the thecae separated widely by an elongate connective perpendicular to the filament; corolla subactinomorphic with 5 ± equal lobes; Australia ........................ ............................................................................... Dicladanthera
43 Stamens not as above, if thecae widely separated then vertically offset to superposed; arrangement of corolla lobes various, but corolla usually ± zygomorphic ...................................................... 44
44 Staminodes present, either free or basally fused to the adjacent staminal filament ....................................................................... 45
44 Staminodes absent ..................................................................... 59
45 Calyx 4-lobed, anterior lobe entire or bifid for less than half its length, anterior and posterior lobes typically much broader than lateral lobes and often enclosing them; corolla arrangement variable, lobes subregular or in a 4 + 1 or 2 + 3 configuration, without a hooded upper lip; staminal filaments?always twisted and crossing near the base............................................................... Barleria
45 Calyx 5-lobed, or if anterior pair of lobes largely fused then corolla markedly bilabiate with ± hooded upper lip; staminal filaments not twisted and crossing near the base............................................. 46
46 Seeds with hygroscopic trichomes present throughout or at least around the rim; corolla either with left-contort or quincuncial aestivation.................................................................................. 47
46 Seeds without hygroscopic trichomes, variously tuberculate, echinate, verruculate, puberulous, tomentellous or smooth; corolla with ascending-cochlear aestivation .......................................... 51
47 Filament curtain absent; corolla with quincuncial aestivation; inflorescences dense secund spikes that can be compounded into complex heads, often with dimorphic fertile and sterile bracts; calyx lobes highly unequal, posterior lobe broadest, lateral lobes narrowest (2 + 2 + 1 configuration) .............................. Lepidagathis
47 Filament curtain present; corolla with left-contort aestivation; inflorescences variable but not dense secund spikes with dimorphic bracts; calyx lobes (sub)equal to somewhat unequal, not in 2 + 2 + 1 configuration....................................................................... 48
48 Corolla tube much longer than lobes, tube either narrowly cylindrical throughout (corolla salverform) or with long cylindrical basal portion and gradually expanded throat; inflorescences a series of spikes, bracts often imbricate and often with conspicuous reticulate patterning ........................................................... Eranthemum
48 Corolla without such a long basal cylindrical tube, not salverform; inflorescences not as above ....................................................... 49
49 Corolla internally with prominent rows of trichomes along posterior surface, these functioning to retain the style; corolla typically with thin but prominent ridge between pair of stamens....... ................................................................................. Strobilanthes
49 Style not held in place by trichomes on corolla tube; corolla without a prominent ridge between pair of stamens ......................... 50
50 Ovary with 4 ovules; lower corolla lip lacking stiff retrorse bristles; anther thecae usually spurred; plants usually of dry ground ......... .................................................................................... Dyschoriste
50 Ovary with 8–20+ ovules; lower lip of corolla with numerous stiff retrorse bristles; anther thecae not spurred; plants of (seasonal) wetlands....................................................................... Hygrophila
51 Ovary with 8 or more ovules, capsule 8–16-seeded; pollen with aperture margins conspicuously thickened and intricately ornamented with conical spines .................................. Phlogacanthus [12]
51 Ovary with 2 or 4 ovules; capsule 2- or 4-seeded; pollen without thickened and ornamented aperture margins ............................. 52
52 Leaves strongly anisophyllous (appearing alternate), larger leaf of a pair 9.5–19 × 2.5–6.7 cm, smaller leaf of a pair reduced to a minute lanceolate blade 4–6 × 1–2 mm; Borneo........................... ............................................................ Ptyssiglottis staminodifera
52 Leaves isophyllous or not so markedly anisophyllous .............. 53
53 Corolla salverform, tube longer than limb and narrowly cylindrical throughout or only slightly widened distally, limb either subequally 5-lobed or only weakly bilabiate, if the posterior pair of lobes partially fused then not forming a hooded upper lip ............ ................................................................. Pseuderanthemum [49]
53 Corolla not salverform, if tube longer than limb and cylindrical, then limb markedly bilabiate with posterior pair of lobes largely fused and sometimes forming a hooded upper lip..................... 54
54 Corolla small, up to 15 mm long but often ≤ 10 mm long......... 55
54 Corolla much larger,> 25 mm long ........................................... 58
55 Leaves with toothed, spinose or sinuate margin; inflorescences axillary, 1-flowered or simple dichasia or fascicles; Australia, New Guinea, Fiji .................................................... Graptophyllum [50]
55 Leaves with ± entire margin; inflorescences spikes or racemes, often terminal.........................................................................56 [51]
56 Corolla campanulate, limb only weakly bilabiate; tube shorter than limb and widened almost from the base; India to Japan and Vietnam ............................................................... Codonacanthus
56 Corolla strongly bilabiate; tube longer than or subequal to limb, not widened from the base......................................................... 57
57 Anther thecae basally muticous; corolla tube sometimes with a dorsal pouch distally; China to Borneo ............. Cosmianthemum
57 Anther thecae with paired basal spurs; corolla tube without a dorsal pouch; China ................................................ Wuacanthus
58 Corolla tube markedly infundibuliform, with basal cylindrical portion and abruptly widened throat; limb only weakly bilabiate, the 5 lobes subequal, upper lip not strongly hooded; corolla white or rose-colored, with intricate darker veins; India, Bhutan, Myanmar, China ..................................................................................... Mackaya
58 Corolla tube more gradually widened from base to apex and ± strongly curved; limb bilabiate with posterior pair of lobes forming a hooded upper lip; corolla red or bright pink; Australia, New Guinea, Pacific Is., naturalized elsewhere ...... Graptophyllum
59 Corolla resupinate through ±180° twist in corolla tube; flowers held between paired clasping bracts .......................................... 60
59 Corolla not resupinate or, if so, then due to twisting of pedicel, corolla tube not twisted; flowers not held between paired clasping bracts ......................................................................................... 61
60 Capsule with fracturing placentae; anther thecae rounded or elliptic............................................................................ Dicliptera
60 Capsule without fracturing placentae; anther thecae (in Asia) typically linear-oblong, rarely rounded or elliptic............................. .............................................................................. [Peristrophe] [36]
61 Anthers with thecae superposed and held patent to one another; corolla with a conspicuously 2-lobed upper lip, each lobe forked; Australia ........................................................ Xerothamnella [52]
61 If anthers superposed and oblique then corolla with a shortly 2-lobed or emarginate upper lip, the lobes not forked............... 62
62 Pollen disc-shaped, bipororate with a broad marginal girdle of sexine [53]; anthers with thecae ± markedly offset to fully superposed and often highly oblique, sometimes 1 or both thecae perpendicular to filament, lacking basal appendages; rugula absent .............. ........................................................................................ Isoglossa
62 Pollen very variable but never disc-shaped with a marginal girdle; anthers with thecae variously held at an equal height to strongly offset, if offset then often with the lower theca or both thecae with a basal appendage, and rugula present ...................................... 63
63 Rugula absent; anther thecae held at the same height or only slightly offset, parallel to each other and to the filament or slightly sagittate; thecae without appendages or with short uncurved appendages....64
63 Rugula present; anther thecae usually offset by at least half their length or fully superposed, sometimes markedly oblique; lower theca or more rarely both thecae often with a conspicuous ± curved appendage, this typically pale.................................................... 79
64 Ovary with 6 or more ovules, capsule 6- to many-seeded, or if 2 ovules per locule and capsule 4-seeded then anthers penicillate at base or thecae only dehiscing via a short slit in central half to 2/3; pollen with aperture margins and/or aperture surface conspicuously thickened and often intricately ornamented with conical spines ......................................................................................... 65
64 Ovary with 2 or 4 ovules; capsule 2- or 4-seeded; anthers not penicillate at base, thecae dehiscing along ± their full length; pollen without thickened and ornamented aperture margins or surfaces ....... 72
65 Filaments swollen (pouched) distally; corolla subequally 5-lobed, not clearly bilabiate ................................................................... 66
65 Filaments not swollen or pouched; corolla bilabiate or subequally 5-lobed....................................................................................... 67
66 Cladodes (reduced abortive branches) present in the inflorescence, terminated by paired small spines; seeds not compressed, with 2 distinct grooves, surface with hygroscopic trichomes; India ......... ................................................................................ Haplanthodes
66 Cladodes absent in inflorescence; seeds somewhat compressed, not distinctly grooved, surface without trichomes, verrucose; widespread ................................................................... Haplanthus [9]
67 Ovary with 4 ovules; anthers glabrous, dehiscent via longitudinal slit in central half or 2/3 of each theca; India, Myanmar ............... .................................................................... Sphinctacanthus [10]
67 Ovary with 6 or more ovules, or if 4 then anthers conspicuously penicillate at base and dehiscent via longitudinal slit in distal half extending to apex....................................................................... 68
68 Capsule linear and 4-angled, not compressed; seeds markedly compressed, smooth, can be covered in trichomes; anthers not penicillate .................................................................................. 69
68 Capsule compressed perpendicular to the septum, elliptic, oblanceolate or narrowly oblong in face view; seeds subglobose, ellipsoid or block-like, not compressed, often pitted or rugose and grooved; anthers often penicillate at base.........................................................71
69 Calyx 4-lobed; slender procumbent herbs; Thailand ....... Graphandra
69 Calyx 5-lobed; habit variable but not procumbent herbs........... 70
70 Corolla tube shorter than limb; upper lip ± curved; India ............. ................................................................................. Diotacanthus
70 Corolla tube longer than limb; upper lip not curved; widespread ........................................................................ Gymnostachyum
71 Capsule 6–20-seeded; India and Sri Lanka to Myanmar, introduced elsewhere....................................................... Andrographis
71 Capsule 4-seeded; India, Sri Lanka ............... [Indoneesiella] [11]
72 Corolla blue-green or livid-green, tube narrowly cylindrical throughout with only very short expanded throat, usually longer than limb, upper lip linear-lanceolate, much smaller than lower lip; India and Sri Lanka to Myanmar ........................................................ Ecbolium
72 Corolla variously colored but not shades of green, tube variously shaped but if longer than limb then more gradually expanded and lips not so unequal..................................................................... 73
73 Inflorescences often on leafless portion of branches or on mature woody stems (ramiflorous or cauliflorous), in fascicles or short spikes; shrubs or small trees ...................................................... 74
73 Inflorescences either terminal or axillary on leafy portion of branches; herbs or shrubs ................................................................. 75
74 Corolla lips conspicuously longer than tube; lower lip strap-shaped with 3 short rounded apical lobes; New Guinea .............. ........................................................................... Calycacanthus
74 Corolla tube longer than lips; lower lip deeply divided into 3 linear-lanceolate lobes; Vietnam ........................................ Cyclacanthus
75 Calyx lobes lanceolate, with 3 or more parallel veins prominent at maturity; corolla with ± markedly saccate throat above short basal cylindrical tube .......................................................................... 76
75 Calyx lobes linear to linear-lanceolate, usually only the midrib prominent or veins inconspicuous; corolla without markedly saccate throat.......................................................................................... 77
76 Inflorescences 1-flowered, these sometimes clustered towards branch tips; anther thecae pubescent; pollen 3-colporate, 6-pseudocolpate; Thailand .............................................................................. Marcania
76 Flowers held in branched thyrses; thecae glabrous; pollen 5-colporate, 10-pseudocolpate; New Guinea ...................................... Jadunia [54]
77 Inflorescences axillary, varying from lax dichasia to reduced and contracted dichasia with 2(–4) contracted branches that can bear several to many pairs of imbricate, scale-like bracts, or sometimes reduced to single flowers; inflorescences not spiciform; Sri Lanka to New Guinea ............................................................ Ptyssiglottis
77 Inflorescences terminal, spiciform or, if branched, then branches spiciform.................................................................................... 78
78 Corolla with strongly curved and hooded upper lip, upper lip either shortly 2-lobed or 4-lobed, lower lip 3-lobed or 1-lobed; inflorescence often branched with branches spiciform, or sometimes unbranched; India and China to Indonesia ................... Leptostachya
78 Corolla with a ± straight and not conspicuously hooded upper lip, upper lip shortly 2-lobed, lower lip 3-lobed; inflorescence spiciform, unbranched; Taiwan .............................. Kudoacanthus [55]
79 Corolla tube narrowly cylindrical, considerably longer than lips; upper lip lanceolate or narrowly so, not hooded; anthers with thecae lacking appendages; widespread ...................... Rhinacanthus
79 Corolla tube not so narrowly cylindrical, if tube longer than lips then upper lip hooded; anther thecae with or (rarely) without basal appendages, often with a conspicuous curved pale appendage on the lower theca........................................................................... 80
80 Capsule with fracturing placentae; inflorescences usually secund spikes with imbricate bracts; bracts with or without conspicuous white or pinkish hyaline margins....................................... Rungia
80 Capsule without fracturing placentae; inflorescences variable, if secund spikes with imbricate bracts then bracts without abrupt pale hyaline margins ......................................................................... 81
81 Capsule 2-seeded, seeds smooth, discoid; India ........ Meiosperma
81 Capsule usually 4-seeded, seeds variously sculptured or rarely smooth; widespread................................................... Justicia [43]
Key to the genera of Acanthaceae in the Americas
Mangrove trees or shrubs with pneumatophores present; fruit a leathery 1-seeded capsule .............................................. Avicennia
Herbs, shrubs, lianas or small trees, if (rarely) mangrove trees or shrubs then pneumatophores lacking (can have aerial prop roots); fruit either a ± woody or thin-walled capsule with 2 or more seeds, or a 1-seeded drupe...................................................................... 2
Seeds not borne on hook-shaped retinacula, retinacula lacking or papilliform; plants without cystoliths; all anthers bithecous......3
Seeds borne on prominent hook-shaped retinacula (retinacula indistinct in Aphanosperma and Chalarothyrsus, with seeds permanently retained in capsule valves); plants with or without cystoliths, if cystoliths absent then anthers monothecous ................................. 7
Herbaceous twiners or lianas; flowers subtended by conspicuous clasping or partially connate paired bracteoles; calyx a subentire or undulate rim or with irregular teeth, or obscurely 5-lobed; fruit a 1-seeded drupe..................................................... Mendoncia [56]
3 Herbs or shrubs, not twining; paired bracteoles present or absent but not large and conspicuous; calyx deeply 4- or 5-lobed; fruit a many-seeded capsule (usually>10 seeds) ................................... 4
4 Peduncles bearing clasping scale-like sterile bracts; all bracts sclerophyllous; leaves in rosettes or whorls either basally or terminating branches (sometimes dispersed along stems in E. imbricata and E. mexicana) ....................................................................... Elytraria
4 Peduncles (if present) without clasping scale-like sterile bracts; bracts membranous or foliaceous; leaves opposite, at least some pairs dispersed along the stems.................................................... 5
5 Bracteoles absent; inflorescence of dense ± cylindrical spikes with imbricate bracts; calyx 4-lobed, the anterior lobe with bifid apex (rarely more deeply divided into 5 lobes); stamens 2, staminodes absent....................................................................... Nelsonia [57]
5 Bracteoles present; inflorescence variable but, if spikes cylindrical, then relatively lax; calyx 5-lobed; stamens 4, adaxial staminode often also present (rarely 2 stamens +2–3 staminodes) ............... 6
6 Plants subcaulescent (internodes indistinct or short); inflorescence of axillary, long-pedunculate (peduncles 9.8–22 cm long) panicles of spikes; ovary asymmetric with style arising on one side, stigma 1-lobed, subcapitate; Brazil ........................................ Aymoreana
6 Plants caulescent (internodes distinct, usually elongate); inflorescence of terminal, sessile to short-pedunculate (peduncles 0.2– 4 cm long) racemes or spikes (rarely panicles); ovary symmetric, stigma 2-lobed (one lobe usually bifid) or subcrateriform (in S. guianensis), lobes not subcapitate; widespread ....... Staurogyne
7 Stamens 4, sometimes also with an additional staminode ........... 8
7 Stamens 2, sometimes also with (1) 2 (3) staminodes ............... 30
8 Anthers all monothecous; plants without cystoliths .................... 9
8 Anthers all bithecous or 2 bithecous and 2 monothecous; plants with cystoliths............................................................................ 14
9 Corolla zygomorphic, the lobes dissimilar in form ................... 10
9 Corolla usually subactinomorphic, the lobes more or less similar in form ........................................................................................... 12
10 Calyx deeply 3-partite; Colombia ........................... Cyphacanthus
10 Calyx 5-partite........................................................................... 11
11 Leaves opposite (rarely subopposite); bracts entire or dentate, green or often brightly colored; corolla rarely with linear nectar guides, mostly 25–85 mm long; at least distal portion of filaments of stamens usually exserted from corolla tube; pollen with colpi not expanded or bifurcating (usually narrowed) toward poles, interapertural exine usually heterogeneously sculptured; widespread ........... Aphelandra [5]
11 Leaves opposite (rarely subopposite) or quaternate; bracts entire and usually green; corolla often with colored linear nectar guides, 6.5–24 mm long (or if larger, to 40 mm, then plants with quaternate leaves); filaments of stamens often entirely included in corolla tube; pollen with colpi sometimes expanded or bifurcating toward poles, interapertural exine homogeneously sculptured; Mexico ..... ................................................................................... Holographis
12 Pollen 3-colpate with each colpus longitudinally bisected by an operculum (elongate band of exine), opercula either isolated within the colpi (operculate) or connected at each end to the interapertural exine (pontoperculate); Jamaica ............................................... Salpixantha
12 Pollen 3-colpate with colpi not bisected by elongate bands of exine or pollen pantoforate (i.e., sometimes in Stenandrium dulce) or pollen pantoaperturate (rugate) with rugae arranged ± tangentially over surface or pollen 3-colpate and with prominent margines and mesocolpial ridges (appearing 9-colpate); widespread, but not in Jamaica ...................................................................................... 13
13 Plants usually small, up to 25(–70) cm; leaves often borne at or near ground level (plants acaulescent to subcaulescent); bracts usually green; pollen 3-colpate or pantoforate (i.e., sometimes in S. dulce) .................................................................... Stenandrium
13 Plants usually shrubby, up to 1.5 m tall; leaves disposed along conspicuous stems; bracts whitish, pinkish, or reddish-brown; pollen pantoaperturate (rugate) with rugae arranged ± tangentially or pollen 3-colpate and with prominent margines and mesocolpial ridges (appearing 9-colpate)........................................ Neriacanthus [6]
14 Stamens with 2 anthers bithecous and 2 anthers monothecous...15
14 Stamens with all anthers bithecous............................................ 20
15 Seeds with hygroscopic trichomes; corolla with quincuncial aestivation...............................................................................................16
15 Seeds without hygroscopic trichomes; corolla with ascending-cochlear aestivation ................................................................... 17
16 Calyx lobes ± homomorphic; plants with axillary spines and/or spiny leaf margins; West Indies..................................... Barleriola
16 Calyx lobes heteromorphic in 2 + 2 + 1 configuration, posterior lobe broadest, lateral lobes narrowest, anterior lobes often partially fused; plants lacking axillary spines and/or spiny leaf margins; widespread........................................................ Lepidagathis [58]
17 Corolla red, colored markings on limb absent, 34–48 mm long, ± tubular or clarinet shaped with the tube elongate, relatively slender but gradually expanded distally and the limb shallow, inconspicuous, tube 6–11× longer than limb; Bolivia, Brazil ................ ............................................................................. Pranceacanthus
17 Corolla white, pinkish or purple, often with colored markings on limb, 10–45 mm long, infundibuliform to salverform and with a ± conspicuous limb (at least the upper lip in Isotheca), tube 1– 2.6 (–3.6) × longer than limb (or if 6 or more times longer than limb as in Isotheca, then corolla white)..................................... 18
18 Corolla white, apparently lacking colored markings on limb, 35– 45 mm long, downward curved and “cobralike” in bud; stamens conspicuously exserted beyond limb of corolla; inflorescence a ± open, terminal dichasiate raceme (i.e., dichasia sessile and flowers pedicellate); pollen 4-aperturate, echinate; Trinidad, Venezuela ...... ............................................................................................. Isotheca
18 Corolla white, pinkish or purple, usually with colored markings on limb, 10–30 mm long, usually straight, not “cobralike” in bud; stamens included in corolla tube or exserted from it, but not extending beyond limb; inflorescence of axillary or usually terminal dichasiate spikes (sometimes very reduced) or panicles of spikes; pollen usually 3-aperturate ................................................................... 19
19 Corolla ± salverform with subactinomorphic limb, upper lip deeply lobed; bracts ± inconspicuous, ca. 1 mm wide; Costa Rica, Brazil, Panama ........................................................... Chamaeranthemum
19 Corolla infundibuliform with bilabiate limb, upper lip entire to shallowly lobed; bracts conspicuous, (2–) 5–20 mm wide; widespread ..................................................................... Herpetacanthus
20 Corolla with ascending-cochlear aestivation; pollen 3-colporate, 6-pseudocolpate......................................................................... 21
20 Corolla with quincuncial or left-contort aestivation; pollen otherwise ................................................................................... 22
21 Perennial herbs or shrubs to 1.5 m tall; calyx to 5 mm long, 5-lobed, lobes homomorphic; corolla red, 15–21 mm long; capsule 12– 18 mm long; seeds permanently retained in capsule and partially fused to inner capsule wall; western Mexico .......... Chalarothyrsus
21 Large shrubs to small trees to 8 m tall; calyx 15–40 mm long, 2-lipped, the 2 segments entire or variously lobed at apex; corolla white to yellow; 23–97 mm long; capsule 40–85 mm long; seeds expelled from mature capsule, not fused to inner capsule wall; eastern and southern Mexico to Costa Rica ................. Spathacanthus
22 Corolla with quincuncial aestivation, lacking a filament curtain; inflorescences mostly secundiflorus ......................... Lepidagathis
22 Corolla with left-contort aestivation, with a filament curtain; inflorescences rarely (if ever) secundiflorus ..................................... 23
23 Calyx 3-lobed;corolla very large,gullet-shaped,pale green to greenish-yellow (sometimes with maroon tinges), cream-colored, or entirely dark maroon; Mexico and Central America ..................... Louteridium
23 Calyx 5-lobed; corolla variable but not as above....................... 24
24 Corolla subcylindrical or, if with an expanded/ampliate throat, then flowers borne in headlike clusters subtended by several pairs of bracts ......................................................................................... 25
24 Corolla campanulate, throat ampliate; flowers not borne in headlike clusters, not subtended by several pairs of bracts............... 26
25 Thecae awned basally; western South America..... Suessenguthia
25 Thecae awnless; Peru .......................................... Trichosanchezia
26 Calyx lobes fused for at least 1/3 of their length and usually over half of their length, with hyaline regions bordering each lobe; anther thecae usually appendaged at base, these sometimes inconspicuous or rarely absent; plants herbaceous or subshrubby............ Dyschoriste
26 Calyx lobes deeply divided, or if with a conspicuous fused portion then lacking hyaline regions bordering each lobe; anther thecae lacking basal appendages or if basally awned (Bravaisia) then plants large shrubs or trees ........................................................ 27
27 Thecae awned with a single, subulate projection ........... Bravaisia
27 Thecae awnless.......................................................................... 28
28 Shrubs or trees up to 25 m tall and usually ≥ 4 m tall; corolla woolly pubescent externally ..................................... Trichanthera
28 Herbs, shrubs, sometimes clambering, or treelets, <4 m tall; corolla various but not woolly pubescent externally......................... 29
29 Corolla usually ≤ 10 mm long, conspicuously bilabiate; plants usually aquatic or semi-aquatic; pollen 4-colporate and 8- (or more? [59]) pseudocolpate, exine usually more or less finely and irregularly reticulate .............................................................. Hygrophila
29 Corolla usually> 10 mm long, subactinomorphic and not conspicuously bilabiate; plants not aquatic but can be riparian; pollen 3-aperturate, lacking pseudocolpi, exine coarsely reticulate ......... ........................................................................................... Ruellia
30 Corolla with left-contort or quincuncial aestivation, with or without a filament curtain................................................................. 31
30 Corolla with ascending-cochlear aestivation, lacking a filament curtain........................................................................................ 34
31 Corolla with quincuncial aestivation, lacking a filament curtain..... 32
31 Corolla with left-contort aestivation, with a filament curtain.... 33
32 Corolla red, strongly bilabiate, upper lip ± hooded, entire or shallowly 2-lobed, lower lip 3-lobed; Mexico ................ Lepidagathis
32 Corolla bright yellow (drying dark purplish), consisting of 5, large, spreading lobes, 4 posterior, 1 anterior; widespread ........ Barleria
33 Calyx 3-partite; corolla very large, gullet-shaped, pale green to greenish-yellow (sometimes with maroon tinges), cream-colored, or entirely dark maroon; primarily nocturnal; shrubs to trees; pollen spherical and pantoforate; Mexico and Central America......... ................................................................................... Louteridium
33 Calyx 5-partite; corolla long and tubular, primarily red or orange, but can be yellow or white; shrubs; pollen not spherical, 2-colporate and polypseudocolpate, the apertural faces oriented 90° from one another; mostly South America........................................ Sanchezia
34 Androecium of 2 stamens (bithecous) and 2 staminodes; flowers sometimes heterostylous............................................................ 35
34 Androecium of 2 stamens (bithecous or monothecous) and 0 staminodes; flowers not heterostylous ........................................... 41
35 Corolla ca. 5 mm long; upper lip divided less than 1/3 its length (i.e., shallowly 2-lobed); Ecuador ........................ Psilanthele [60]
35 Corolla (at least of chasmogamous flowers)> 5 mm long (up to 45 mm long and usually> 10 mm long); upper lip divided 1/2 or more its length (shallowly 2-lobed in Chileranthemum and some species of Odontonema) ............................................................ 36
36 Corolla with purplish spots on limb, the 2 lobes of upper lip strongly laterally divergent from each other; stamens conspicuously exposed between lips of corolla (not appressed to upper lip of corolla), filaments arched toward lower lip of corolla; plants not heterostylous; South America.................................................. Pulchranthus
36 Corolla with or without spots on limb, the 2 lobes of upper lip not laterally divergent from each other; stamens appressed to upper lip of corolla or exposed between lips, filaments straight (not curved toward lower lip of corolla); plants often heterostylous...................37
37 Corolla ± salverform, tube elongate and cylindric (or throat becoming slightly expanded) or sometimes narrowed distally, limb ± rotate, usually subactinomorphic.................. Pseuderanthemum
37 Corolla infundibuliform, tube expanding gradually or ± abruptly toward mouth (sometimes subcylindric), limb extending forward to reflexed, bilabiate .................................................................. 38
38 Trailing or clambering shrubs; leaves coriaceous, blades 10–25 mm long; corolla 13–17 mm long; serpentine substrates in Cuba ........... .............................................................................................. Sapphoa
38 Plants lacking the above combination of characters .................. 39
39 Armature usually present in leaf axils (absent in some plants or in some species); leaves usually coriaceous; corolla usually bluish to purple (rarely red or white); Argentina, Bolivia, Peru, West Indies .................................................................................. Oplonia [61]
39 Spines absent; leaves membranaceous; corolla red, purplish, pink, yellow, or white ......................................................................... 40
40 Corolla purplish to pinkish to whitish with colored markings on the lower lip, tube subcylindric to ± abruptly expanded distally, shorter to only slightly longer than limb, upper lip shallowly 2-lobed, erect, lower lip horizontally spreading (i.e., lips 90° apart with lower lip forming a conspicuous “landing platform”); plants not clambering; Mexico to El Salvador ..................................... Chileranthemum
40 Corolla red, pinkish, or purplish (rarely yellow or white), usually lacking colored markings, tube usually gradually expanded distally and longer (often>1.5× longer) than limb, upper lip shallowly to ± deeply 2-lobed, upper and lower lips variously oriented; plants sometimes clambering; widespread.......................... Odontonema
41 Anthers monothecous ................................................................ 42
41 Anthers bithecous ...................................................................... 43
42 Inflorescence of terminal spikes; corolla violet, tube cylindric, limb deeply 5-lobed with equal lobes; Brazil ................................ ............................................................ Sebastiano-Schaueria [62]
42 Plants not with the above combination of characters; widespread ....................................................................... Stenostephanus
43 Stems usually hexagonal; flowers in bracteate dichasia bearing 1 or more cymules, cymules of 1 or more flowers subtended by an involucre of 2 or more pairs of bracteoles (outer pair usually conspicuous and larger than inner pair(s)); capsules with fracturing placentae, dehiscent capsule conspicuously ruptured near base of head; corolla resupinate (180° or 360°) in some species; widespread ............................................................................ Dicliptera
43 Stems terete to quadrate to quadrate-sulcate (rarely subhexagonal); flowers rarely borne in cymules but, if so, then not as described above; capsules without fracturing placentae (or retinacula slightly separating from inner wall in Henrya and Tetramerium, but then not rising to protrude prominently from each capsule valve on/after dehiscence); corolla not resupinate............................................ 44
44 Corolla subsalverform, purplish; stamens 2–2.5 mm long, filaments apically pubescent with flexuose eglandular trichomes, thecae superposed (0.3–0.5 mm apart), distal theca fertile, proximal theca sterile (appendage-like); seeds ca. 5 mm in diam., papillose, margin swollen............................................................. Streblacanthus
44 Plants not with the above combination of characters................. 45
45 Upper lip of corolla with a rugula on the internal surface (not confirmed for all taxa); flowers nototribic; anther thecae with or without basal appendages, the pair parallel to perpendicular and equally to unequally inserted on the filament; pollen 2–6 (or more?)-aperturate, pseudocolpi present or absent, insulae (i.e., ± isolated [sometimes linked in Poikilacanthus] [63] gemmate regions enclosed by thick, smooth marginal walls) and/or peninsulae (attached on one side to the interapertural exine), when present, usually restricted to 1 or more rows flanking apertures or entire interapertural surface either reticulate or covered with smooth and subconic to rounded verrucae..........................................................................................46
45 Upper lip of corolla lacking a rugula; flowers sternotribic, nototribic or pleurotribic; anther thecae lacking basal appendages, the pair parallel to subsagittate and equally to subequally inserted on the filament; pollen 3-colporate and 6-pseudocolpate (pseudocolpi sometimes fused, inconspicuous, or rarely absent; 2-colporate, 4- pseudocolpate in Mexacanthus), insulae and peninsulae absent ...53
46 Shrubs or epiphytic herbs; flowers subtended by an involucre of conspicuous, basally fused bracteoles; corolla red or lilac; calyx highly reduced, cupular, entire to shallowly dentate; Brazil .......... .................................................................................... Clistax [64]
46 Plants not with the above combination of characters................. 47
47 Inflorescence of short, axillary, pedunculate, subcapitate spikes; bracts oblanceolate to obovate; thecae of a pair superposed and perpendicular; corolla yellow-green with purplish spots on lower lip, ca. 9 mm long; Andean Peru ......................... Cephalacanthus
47 Plants not with the above combination of characters................. 48
48 Trees to 5 m tall; leaves with globose (appearing hemispheric on surfaces) concretions 0.3–0.7 mm in diam.; thecae of a pair equally inserted, parallel to subsagittate, lacking basal appendages; calyx 25–32 mm long, lobes oblong to oblanceolate, widely spreading at maturity; capsule 22–29 mm long; Haiti .............. Samuelssonia
48 Plants not with the above combination of characters................. 49
49 Pollen 4–6 (or more?)-porate, interapertural surfaces either covered with discrete insulae or with insulae linked by sharing common end-walls and arranged in loops that enclose a row or band of linked insulae ........................................................................ 50
49 Pollen 2–4-aperturate (colporate or porate), apertures flanked by pseudocolpi or by 1 or more rows of ± discrete insulae and/or peninsulae, or the entire interapertural surface covered with smooth and subconic to rounded verrucae ............................................. 51
50 Inflorescence large, usually longer than 7 cm, and very showy with conspicuous subfoliose red to maroon to pinkish bracts and bracteoles; corolla white (sometimes turning pinkish with age); pollen covered with discrete insulae; frequently cultivated, presumably native in Venezuela ...................................... Megaskepasma [65]
50 Inflorescence various, but not as described above, usually less than 7 cm long; corolla red, orangish, pink, pinkish-purple, greenish-yellow, or white; pollen covered with discrete insulae or pollen otherwise; widespread ........................................... Poikilacanthus
51 Erect shrubs to 3 m; corolla primarily nocturnal, greenish, pale yellow, or cream, 38–95 mm long, upper lip arched, lobes of lower lip usually dangling and somewhat twisted; thecae 5–7.6 mm long; pollen 3-colporate and with either a pseudocolpus or 1 row of insulae flanking each colporus; Brazil ..................... Harpochilus [66]
51 Plants not with the above combination of characters................. 52
52 Subscandent shrubs; corolla greenish white, 13–14 mm long, upper lip erect (i.e., continuous with tube) and lower lip horizontal at maturity (i.e., spreading 90° from upper lip); pollen 4-colporate, mesocolpia “occasionally” [fide Raj, 1961] with 2 pseudocolpi; Cuba ................................................................................... Dasytropis
52 Plants not with this combination of characters and extremely variable in vegetative, floral, and palynological morphologies; widespread ........................................................................ Justicia [67]
53 Inflorescence a terminal thyrse; corolla bud strongly arched (i.e., curved downward and appearing like an upside-down hook), open corolla with the limb curved downward forming an upside-down “U” or semi-circle; thecae 5–6 mm long; Cuba ..... Ancistranthus
53 Plants not with the above combination of characters; not occurring in Cuba ...................................................................................... 54
54 Bracteoles of a pair fused along one side from base to near apex forming a sheathing involucre around flower; pollen with colpi broad, far exceeding the width of the centrally positioned ora; septa and attached retinacula separating slightly from inner wall of mature capsules near base of head; U.S.A. (Arizona) to Costa Rica ........................ Henrya
54 Bracteoles of a pair not fused, or if so only at base up to 1 mm; pollen with colpi narrow, not or only slightly exceeding width of centrally positioned ora; septa and attached retinacula not separating from inner wall of mature capsules (except in Tetramerium).......55
55 Capsules progressively reflexing during maturation (upside-down at maturity), distal portion of capsule expanded, truncate and widest at apex, basal portion of capsule densely pubescent with apically hooked (uncinate) trichomes; seeds 2, permanently enclosed in capsule valves; northwestern Mexico ........................... Aphanosperma
55 Capsules not reflexed at maturity, distal portion of capsule tapering to a point or rounded at apex, basal portion lacking uncinate trichomes; seeds 2–4, free from capsule valves when mature ............ 56
56 Flowers sternotribic (i.e., stamens positioned near lower lip of corolla and anthers dehiscing toward upper lip) or pleurotribic (i.e., anthers dehiscing toward center of floral axis and each other); primarily North and Central America ............................................ 57
56 Flowers nototribic (i.e., stamens positioned near upper lip of corolla and anthers dehiscing toward lower lip) or sternotribic in Schaueria litoralis from South America; mostly South America..................61
57 Flowers pleurotribic; seeds usually 2 per capsule...................... 58
57 Flowers sternotribic; seeds 2–4 per capsule............................... 59
58 Corolla 6.5–11 mm long, cream with maroon markings; pollen 3- colporate, 6-pseudocolpate; southern Mexico ........ Gypsacanthus
58 Corolla 17–26 mm long, bicolored with upper lip red and lower lip yellow; pollen 2-colporate, 4-pseudocolpate; west-central Mexico ................................................................................. Mexacanthus
59 Inflorescence of usually densely bracteate, 4-sided spikes; bracts conspicuous, usually concealing the calyx; septa and attached retinacula separating slightly from inner wall of mature capsules near base of head.............................................................. Tetramerium
59 Inflorescence neither densely bracteate nor 4-sided; bracts inconspicuous and sometimes caducous, not concealing the calyx; septa and attached retinacula not separating from inner wall of mature capsules ..................................................................................... 60
60 Shrubs to 4 m tall, rarely dying back to woody caudices; corolla (white) pink, red, or orange (yellowish), lacking conspicuous colored markings, (24–) 30–65 mm long, tube usually conspicuously ampliate toward apex, (10–) 14–31 mm long; thecae 2.2–4.8 mm long; U.S.A. to Costa Rica ...................................... Anisacanthus
60 Perennial herbs to weak shrubs up to 1 (–1.5) m tall, usually dying back to woody caudices; corolla white, yellow, blue, purple, or pinkish, usually with conspicuous colored markings on the limb, 5.5–23 (–27) mm long, tube not or only slightly ampliate toward apex, 1.5– 8.5 (–13) mm long; thecae 0.5–1.9 mm long; widespread ............... ..................................................................................... Carlowrightia
61 Creeping perennial herbs; leaves with conspicuous white, pink, or red veins; corolla yellow, 10–15 mm long; inflorescence of densely bracteate terminal spikes; Colombia and Brazil to Bolivia .... .......................................................................................... Fittonia
61 Plants not with the above combination of characters................. 62
62 Inflorescence of axillary and terminal, densely bracteate spike-like thyrses to 15 cm long; bracts and calyx lobes distally dark maroon; corolla yellow, (28–) 35–47 mm long, throat abruptly and broadly expanded from subcylindric tube, appearing saccate; northeastern Mexico ........................................................................ Hoverdenia
62 Plants not with the above combination of characters [68] ......... 63
63 Shrubs; bracts and bracteoles inconspicuous and often caducous, 0.8–3 mm long, 0.2–1 mm wide; corolla red, 20–45 mm long; seasonally dry forests of Argentina, Bolivia, Brazil, Paraguay .......... ..................................... Thyrsacanthus (in part, excl. T. sulcatus)
63 Plants not with the above combination of characters................. 64
64 Corolla subsalverform, tube elongate, 1.3–8.5× longer than limb, narrow (up to 1.5 mm in diam. near midpoint, measured flat), and cylindric for most of its length (± abruptly expanded only near apex, if at all)............................................................................. 65
64 Corolla infundibuliform, tube ± gradually expanded distally, 0.7–3 (–3.6) × longer than limb, mostly neither conspicuously narrow ([1.2–] 1.5–6.3 mm in diam. near midpoint, measured flat) nor cylindric through most of its length .......................................... 67
65 Inflorescence of open and elongate spikes, bracts inconspicuous, rachis clearly visible; corolla tube 3–8.5× longer than limb; Costa Rica to Argentina ...................... Pachystachys (in part [69])
65 Inflorescence of densely and conspicuously bracteate ± 4-sided spikes, rachis not visible; corolla tube 1.3–3× longer than limb..... 66
66 Bracts lanceolate, 2–4 mm wide; Argentina, Paraguay, Uruguay .... ................................................................... Thyrsacanthus sulcatus
66 Bracts ovate, broadly ovate, subdeltate, elliptic or subcircular, 5– 18 mm wide; U.S.A. to Mexico ....................................... Yeatesia
67 Corolla bluish or purplish, 11–21 mm long; arid regions of northern Mexico ................. Mirandea (in part, excluding M. sylvatica)
67 Corolla white, yellow, orangish, red or pink, 8–70 mm long; plants of moist to wet forests in southern Mexico to South America.....68
68 Corolla yellow to white, 8–31 mm long; Mexico, Guatemala .....69
58 Corolla white, yellow, orangish, red or pink, 10–70 mm long; South America and the West Indies ...................................................... 70
69 Bracts 1–4 mm long, 0.5–0.8 mm wide; calyx 2–3.7 mm long; corolla 8–13.5 mm long; southern Mexico .......... Mirandea sylvatica [70]
69 Bracts 9–22 mm long, 1.2–2.2 mm wide; calyx 10–25 mm long; corolla 22–31 mm long; Mexico, Guatemala ................................ .............................................................. Schaueria parviflora [71]
70 Corolla yellow or white; bracts narrow, 0.5–2.5 mm wide, mostly yellow in species with yellow corollas and green in species with white corollas; Atlantic forests of Brazil ...................... Schaueria
70 Corolla mostly red, orange-red or pink (white in P. lutea, and yellow in P. azaleiflora); bracts (4–) 6–18 mm wide in most species (1–1.5 mm wide in P. azaleiflora, P. badiospica, P. gracilis and P. linearibracteata), green to yellowish-green (bright yellow to orange-yellow in P. lutea and brownish red in P. badiospica); West Indies and Amazonian South America, especially Peru ................ ................................................................................. Pachystachys
description: Published as part of Manzitto-Tripp, Erin A., Darbyshire, Iain, Daniel, Lucinda A. McDade Thomas F. & Kiel, Carrie A., 2022, Revised classification of Acanthaceae and worldwide dichotomous keys, pp. 103-153 in TAXON 71 (1) on pages 125-137, DOI: 10.1002/tax.12600, http://zenodo.org/record/14047424