Homalium (sect. Eumyriantheia) Warb. 1893
Creators: name: Wendy L. Applequist
Publisher: name: Zenodo
Year: 2016
Subjects: Biodiversity
Taxonomy
Plantae
Tracheophyta
Magnoliopsida
Malpighiales
Salicaceae
Homalium

description: Homalium sect. Eumyriantheia Warb. in Engler & Prantl, Nat. Pflanzenfam. III(6a): 36. 1893.
Ξ Myriantheia Thouars, Gen. Nov. Madagasc.: 21. 1806. Ξ Homalium [unranked as §] Myriantheia (Thouars) Baill. in Bull. Mens. Soc. Linn. Paris 1: 576. 1886 [as Myrianthea]. Ξ Homalium sect. Myriantheia (Thouars) Kuntze in Post & Kuntze, Lex. Gen. Phan., Prop.: 285. 1903 [as Myriantheja].
Typus: Homalium laxiflorum (Tul.) Baill. (Ξ Myriantheia laxiflora Tul.) (designated by Sleumer, 1973: 315).
Trees. Leaves with stipules usually caducous (rarely in part persistent); secondary veins brochidodromous, little or not prominent; texture fairly thick to coriaceous. Inflorescences racemose or paniculate, lateral (in part pseudoterminal or clustered at apices); flowers pedicellate (sessile), often with bracteoles borne on pedicels, dehiscing immediately or slightly below flower shortly after anthesis. Flowers with sepals and petals numbering 4 to 5 (seldom 6), not markedly accrescent nor highly reduced; sepals not (or inconsistently) reflexed; petals obovate to oblanceolate (in H. trigynum to spatulate, with sepals then ovate), not ciliate (except through pubescence of entire adaxial surface); calyx cup usually more or less funnelform (rarely shortly so, or in H. trigynum cylindrical with a broad rounded base); stamens inserted just below base of, but not adnate to petals in groups of 3 (aberrantly 4; in H. boinense consistently 5) with two in each fascicle attached at the sides of the neighboring sepal glands; anthers 0.2-0.5 mm, dorsifixed below midpoint and often somewhat versatile, dehiscing by longitudinal sutures, united by a broad connective so that the thecae are parallel or almost parallel with their adjoining lateral surfaces appressed; styles fused at base. Fruits, where known, usually containing 1 to 2 maturing seeds (possibly several-seeded in one species); inner surface of ovary glabrous (sparsely pubescent).
Notes. – Sleumer (1973) wrongly corrected the name of sect. Eumyriantheia to Myriantheia and treated it as having been based upon the generic name Myriantheia Thouars. Under Art. 21.3 of the ICN (McNeill et al., 2012), Eumyriantheia could not have been validly published as a section within Myriantheia if that genus had been recognized, but it is legal within Homalium. Myriantheia does not enjoy priority at the sectional level, and Eumyriantheia could have been published either as a replacement name for it or as the name of a new taxon. However, since Sleumer considered the two to be nomenclatural synonyms, his designation of a type for one of them can be considered applicable to both.
The traditional circumscription of sect. Eumyriantheia is excessively broad. It was distinguished from other fasciculatestamened sections largely by its lack of the apomorphic characters that were said to characterize those sections; thus it has been defined by plesiomorphic characters, and encompassed a suspicious degree of variation. South Asian, Malesian and Pacific species (see Sleumer, 1954; Lescot, 1970, 1980) have 7 to 12 (rarely 6) narrowly oblong to narrowly elliptical sepals and petals, which are similar in shape, or the sepals shorter and narrower, and long-ciliate or long-pubescent throughout; the calyx cup is usually subcylindrical and prominently ridged and the anthers very small in proportion to the long slender filaments. Flowers of most of these species closely resemble typical flowers of the widespread sect. Blackwellia, except that sect. Blackwellia has only 1 stamen per petal.
By contrast, the Malagasy species of sect. Eumyriantheia (including the type of the section) have 4 to 5 (rarely 6) sepals and petals, which are relatively broad and variable in shape (the petals often being obovate) and lack long cilia; the calyx cup is usually funnelform or cup-shaped and the anthers different in shape and usually larger. In overall appearance, these species bear much less resemblance to the fasciculate-stamened Asian and Pacific species than to some solitary-stamened Malagasy species. The distribution of morphological variation in Homalium (and allied genera such as Calantica Jaub. ex Tul.) makes it evident that some character(s) must have evolved homoplasiously. It is this author’s opinion that changes in stamen number are clearly homoplasious, and that neither subg. Homalium nor subg. Blackwellia as traditionally defined are natural groups. The exclusion of the Asian and Pacific species from sect. Eumyriantheia into a restored sect. Polyanthera will therefore be proposed (Applequist, unpubl. data).
Almost no fruiting material is available of sect. Eumyriantheia, as recircumscribed to comprise only the Malagasy species; fruits with large (to 2 mm) developing seeds are very rare even in well-collected species. It appears that fruits dehisce promptly as seeds mature. Most flowering parts, except for anthers, usually persist until the maturing fruit is lost as a unit. Species circumscriptions and keys therefore rely solely on flowering characters.
Key to the Malagasy species of Homaliumsect. Eumyriantheia
1. Stamens in groups of 5; dry forest, Mahajanga ....................................... 1. H. boinense
1a. Stamens in groups of 3 (aberrantly 4); humid and littoral (very rarely to dry) forests, widespread............. 2
2. Calyx cup cup-shaped, usually elongated, or cylindrical with a broad rounded base; pedicel 0.5-1 (rarely to 3) mm or absent; petals <3.5 mm with acute apices.................................... 15. H. trigynum
2a. Calyx cup usually funnelform at anthesis (to cup-shaped in fruit or rarely cylindrical); pedicel usually> 1 mm; petals variable, usually> 3.5 mm (rarely <3.5 mm then apices rounded).............................. 3
3. Abaxial surface of both sepals and petals densely (to moderately) pubescent over most of surface, often less dense at apical margins........................ 4
3a. Abaxial surface of sepals and petals sparsely or minutely pubescent to glabrous, or portions of the petals densely pubescent but the sepals glabrous to sparsely (moderately) pubescent (in one species moderately pubescent, densest at base and along margins)...................... 7
4. Upper surface of sepal glands at least partly pubescent.............................. 9. H. oppositifolium
4a. Upper surface of sepal glands glabrous............ 5
5. Sepals 4 (rarely 5), 3-5.5(-6.5) mm, broadly oblong to broadbased obovate or oblong (rarely broadly elliptical) with rounded apex; petals 3.6-6.2 mm, normally significantly longer than sepals (aberrantly equal in length); neither petals nor sepals at all keeled; petals very densely pubescent at least near base, with fairly short trichomes........................................... 6. H. laxiflorum
5a. Sepals 5 (seldom 4 or 6 in H. brevipedunculatum), 4.5- 8.4 mm, oblong-lanceolate or elliptical (to obovate) with acute (to obtuse or rounded) apex; petals 4.5-9 mm, slightly longer than (about equal to) sepals; petals and/ or sepals usually slightly keeled towards apex; petals usually in part densely sericeous with long trichomes.... 6
6. Leaves subopposite to alternate (especially proximally), obovate (narrowly or broadly obovate, elliptical), (3.7-) 5.1-11 × 2.1-5.8(-6.5) cm with petiole 3-12(-17) mm; inflorescences 1.5-4(-5.3) cm; abaxial surface of sepals and petals densely pubescent to sericeous (usually only on petals); sepals often shallowly keeled only at apex, petals usually shallowly keeled; petals oblanceolate to narrowly obovate, 4.5-8.5 × 1.8-3 mm ...................................... 2. H. brevipedunculatum
6a. Leaves usually alternate (seldom subopposite), elliptical to obovate (broadly obovate), (5.5-)6.5-18 × (3-) 4-9 cm with petiole 7-23 mm; inflorescences (1.5-)2.3-10(-13.5) cm; abaxial surface of petals and sometimes sepals densely sericeous; sepals usually shallowly keeled for half or more of length, petals usually with a thick streak of very dense indument along central axis but not noticeably keeled; petals obovate to broadly obovate with a narrowed base, 5.5-9 × 3.4-5 mm ....................... 8. H. nobile
7. Sepals 5.5-6.6 mm, petals 9-10.5 mm; abaxial surface of sepals usually with a conspicuous broad pale margin more densely pubescent than remainder of surface.................................... 10. H. pseudoboinense
7a. Sepals to 4.6 mm, petals to 6.5 mm; abaxial surface of sepals glabrous to sparsely (moderately, minutely) pubescent throughout, the indument not denser near margins..... 8
8. Upper surface of sepal glands densely (to moderately) pubescent...................................... 9
8a. Upper surface of sepal glands glabrous to glabrate, or sparsely or partially pubescent.................. 11
9. Leaves narrowly obovate to narrowly elliptic or oblongelliptic or obovate; sepals 3.7-4.6 mm; petals moderately longer than sepals; littoral or low-elevation forest....................................... 4. H. dorrii
9a. Leaves elliptical (to narrowly or broadly elliptical, obovate) or broadly obovate (to obovate, broadly elliptical); sepals <3.5 mm; petals almost twice as long as sepals; mid-elevation humid forest.............. 10
10. Leaves elliptical (to narrowly or broadly elliptical, obovate); leaf margins toothed or wavy with multiple glands in marginal projections; inflorescences racemose.............................. 7. H. maringitra
10a. Leaves broadly obovate (to obovate, broadly elliptical); leaf margins revolute, often strongly, to subentire with 0 to 2 basal glands sunk in margins; inflorescences paniculate with well-developed branches...................................... 13. H. ranomafanicum
11. Inflorescences all or almost completely racemose, with flowers borne singly or in groups of 1-3 on a ridged rachis (at most, clustered flowers rarely forming a very short branch).................................... 12
11a. Inflorescences paniculate, sometimes spiciform with most flowers borne in clusters on short side branches.... 13
12. Leaves oblanceolate to elliptical or narrowly elliptical, 4-9(-13.7) × 1.5-3.6(-4.4) cm; base cuneate to convex or attenuate; apex cuspidate to rounded (acute); leaf margins with 2-4 small basal glands per side; rachis and pedicels usually glabrous (sparsely pubescent); sepal glands 0.6-1 × 0.4-0.5 mm; abaxial surface of petals pubescent with short appressed hairs most densely on central basal portion, less so towards margins, usually with a dark line down the center but not a broad glabrate stripe; Toliara .................... 11. H. pulchrum 12a. Leaves elliptical to obovate, 6-11.5 × 2.8-6.2 cm; base convex; apex rounded to rounded-cuspidate, roundedobtuse or emarginate; leaf margins with 1-2 small basal glands per side; distal part of rachis and pedicels minutely pubescent; sepal glands 0.9-1.6 × 0.7-1 mm; abaxial surface of petals moderately to densely short appressedpubescent with a conspicuous glabrate stripe along the central axis; Toamasina ............. 14. H. schatzii
13. Leaf margins crenate-serrulate for most of length; panicles borne mostly in pairs along length of older twigs, with an open slender appearance, many having one or more well-developed lower branches sometimes subtended by foliose bracts; petals usually only slightly longer than sepals; sepal glands entirely glabrous; lowelevation forest, Antsiranana ...... 5. H. graciliflorum
13a. Leaf margins subentire or revolute (occasionally with few glandular teeth); panicles borne singly except when clustered at twig apices, usually confined to younger distal portions of twigs, usually mostly spiciform with very short branches (in part with few well-developed branches, these then not subtended by foliose bracts); petals normally significantly longer than sepals; sepal glands sometimes in part sparsely pubescent in the depressed central portion.................................... 14
14. Leaves obovate to elliptical, often broadly (rarely to suborbicular, narrowly elliptical, or oblanceolate), (2.5-) 4-7.5(-10.2) × (1.5-)2.1-4.3(-5.1) cm; base cuneate to convex (slightly attenuate); apex rounded (roundedobtuse, shallowly emarginate or rounded-cuspidate, rarely acute or short-acuminate with a rounded tip); margins revolute to subentire or bearing few shallow teeth, with small glands sometimes present and variably placed; panicles normally all spiciform; sepals and petals 4; highto mid-elevation forest; Antsiranana ... 3. H. capuronii
14a. Leaves elliptical to obovate or broadly (narrowly) elliptical, 6-12.5 × 2.8-6.6 cm; base convex to rounded, at extreme base short-attenuate; apex rounded-acute to cuspidate, rounded, or shallowly emarginate; margins minutely revolute with 0 to 2 basal glands just inside margin; panicles sometimes with short but well-developed lower branches; sepals and petals 4(-5); low-elevation forest; Toliara (Marovony).................................... 12. H. randrianasoloi
description: Published as part of Wendy L. Applequist, 2016, Revision of the Malagasy species of Homalium sect. Eumyriantheia Warb. (Salicaceae), pp. 33-60 in Candollea 71 (1) on pages 34-36, DOI: 10.15553/c2016v711a7, http://zenodo.org/record/161516