Xylopia amplexicaulis Baill.
Creators: name: Johnson, David M.
name: Murray, Nancy A.
Publisher: name: Zenodo
Year: 2020
Subjects: Biodiversity
Taxonomy
Plantae
Tracheophyta
Magnoliopsida
Magnoliales
Annonaceae
Xylopia
Xylopia amplexicaulis

description: 1. Xylopia amplexicaulis (Lam.) Baill.
(Figs 5; 6A)
Adansonia; Recueil d’Observations botaniques 4: 142 (1864). — An [n] ona amplexicaulis Lam., Encyclopédie méthodique, Botanique 2 (1): 127 (1786). — Pseudannona amplexicaulis (Lam.) Saff., Journal of the Washington Academy of Sciences 3: 18 (1913). — Type: Mauritius. “ Madagascar ”, s. d. (fl.), Commerson s. n. (lecto-, here designated, P[P030364]!).
MATERIAL EXAMINED. — Mauritius. Without definite locality, s.d. (fl.), Ayres 11 (MAU [MAU 0000966]); without definite locality, s. d. (fl.) [presented in 1863], herb. Blackburn s. n. (K); Pér [r] ier (reserve), s. d. (fl., in spirit collection only, see Fig. 5), Bosser 21824 (P[P01954053]); upland forests, without definite locality, s. d. (st.), Bouton 10 (MAU [MAU0000986]); Île de France, without specific locality, Commerson s. n. (B fragment, FI-W, G[G197204/2, G197204/1], MPU[2 sheets], P[P030363, P01954064, P01954065, Drake Herb. ex Herb. Richard, P 01954066]); Crown Land Perrier in the National Reserves, 21.III.1950 (fl.), Duljeet F. D. 77 (MAU [MAU0000961, MAU0000962]); without definite locality, Herbier du Petit-Thouars s. n. (P[P01954067]); Gaulettes serrées, 20°12’40”S, 57°38’23”E, 8.XII.1998 (st.), Florens et al. 22975 (MAU [MAU0000982]); without definite locality, 1858 (fl.), Grey s. n. (K); Perrier Nature Reserve, 5.III.1974 (fl.), Guého 16133 (MAU [MAU0000984, MAU00000985]); Perrier Nature Reserve, near Mare aux Vacoas, 1800 ft, 3.II.1973 (fl.), Lorence M 57 (MO); Perrier Nature Reserve, 14.III.1975 (fr.), Lorence 1180 (MAU [MAU0000988, spirit collection only]); Bel Ombre forest reserve, 200-400 m, 16.II.1979 (buds), Lorence & Lecordier 2405 (K n.v., MAU [MAU0000983], MO); Perrier Nature Reserve, near Mare aux Vacoas, 600 m, 14.III.1979 (fl.), Lorence 2535 (K n.v., MO, P); Grand Port, s. d. (fl.), Wallich s. n. (BM).
DISTRIBUTION, ECOLOGY AND CONSERVATION STATUS. — Xylopia amplexicaulis is restricted to the island of Mauritius (Fig. 7), where it occurs in forests and thickets, sometimes along streams and sometimes in habitats dominated by Sideroxylon species, at elevations of 200-600 m. Baker (1877) reported it as occurring in mountain woods at Nouvelle Découverte and La Savanne, but no specimens from these localities have been seen; C. Baider (personal communication) lists the localities where the plant has most recently been observed and photographed as Perrier, Bel Ombre, Gaulettes Serrées, Mt. Lion, Brise Fer, Mare Longue/Machabe, and Florin. Specimens with flowers have been collected in February and March and with fruits in March. The species was initially assessed as Endangered by Page (1998a), and is currently listed as Critically Endangered on the IUCN Red List. In 1998 it was only known from 20 mature trees distributed across three localities on the island. Our EOO and AOO estimates of 334 km 2 and 16 km 2, respectively (Table 2), support the assessments.
DESCRIPTION
Tree up 5 m tall; d.b.h. 6 cm.
Twigs glabrous or sparsely appressed-pubescent, the hairs 0.1- 0.2 mm long, but soon glabrate; number of axillary branches per node unknown.
Leaves with larger blades 9.7-13.4 cm long, 5.5-7.0 cm wide, subcoriaceous, discolorous, dull green to brown adaxially, tan and occasionally somewhat glaucous abaxially, ovate to lanceolate, apex acute, obtuse, rounded, or emarginate, base cordate-auriculate with the c. 1 cm long lobes clasping the stem, margin flat, not revolute, glabrous on both surfaces; midrib concolorous with blade adaxially, secondary veins weakly brochidodromous, 13-15 per side, diverging at 65-70° from midrib, these and higher-order veins slightly raised and forming a conspicuous reticulum on both surfaces; petiole 0-2 mm long, broad and flattened, wrinkled, glabrous.
Inflorescences axillary, 1-2-flowered, if more than one flower then peduncle present, sparsely appressed-pubescent except for distal half of peduncle, which is glabrous and sometimes glaucous; peduncle c. 3.4 mm long; pedicels 1-2 per peduncle, 7-15 mm long, 2-2.2 mm thick; bracts 3-4, on proximal half of pedicel, caducous or occasionally with distal bract persistent, distal bract 1.7-4 mm long, semicircular; buds oblong, apex obtuse.
Sepals erect to slightly spreading at anthesis, c. ¼-connate, 5-8 mm long, 6.5-7 mm wide, coriaceous, broadly triangular and concave, apex acute, sparsely pubescent abaxially.
Petals creamy white, wine-colored with a white patch at the base adaxially and with a pink to purple tinge on the outer petals abaxially in vivo; outer petals possibly erect at anthesis, fleshy, 31-45 mm long, 10-14 mm wide at base, 14-15 mm wide at midpoint, fleshy, oblong, flat, apex obtuse, keeled on apical ¼-¹⁄5 but becoming concave toward the base adaxially, densely but finely appressed-pubescent abaxially; inner petals with position at anthesis unknown, c. 26 mm long, c. 4 mm wide at base and midpoint, fleshy, lanceolate, laterally compressed, apex acute, base concave with undifferentiated margin, indument not determinable.
Stamens c. 400; fertile stamens 0.9-1.2 mm long, narrowly oblong, anther connective apex 0.1-0.2 mm long, depressedglobose to bluntly conical, slightly overhanging anther thecae, papillate, anthers 13-14-locellate, filament 0.3-0.4 mm long; outer staminodes 0.8-1.0 mm long, oblong, apex truncate to rounded; inner staminodes c. 0.9 mm long, oblong to quadrate, apex truncate; staminal cone c. 3.5 mm in diameter, c. 0.9 mm high, completely concealing the ovaries, rim even.
Carpels c. 25; ovaries 0.9-1.3 mm long, lanceolate-oblong, glabrous, stigmas loosely appressed, c. 1 mm long, filiform, glabrous.
Fruit of c. 17 monocarps borne on a pedicel 25-30 mm long, glabrate; torus c. 10.5 mm in diameter, c. 9 mm high, depressed-globose; monocarps with light yellow faintly glaucous exterior and bright red endocarp in vivo, 2-4.5 cm long, 0.6- 1 cm wide and thick, clavate to fusiform, not torulose, apex obtuse, base gradually contracted into a stipe 8.8-10 mm long, 1.7-3.4 mm thick, smooth, glabrous; pericarp thin, leathery.
Seeds up to 6 per monocarp, in a single row, oblique to parallel to long axis, 10-12 mm long, 4-5 mm wide, narrowly ellipsoid, circular in cross-section, black, smooth, shiny, perichalazal ring not evident; sarcotesta absent; aril translucent white in vivo, bilobed, lobes c. 3.8 mm long and wide, fleshy, semicircular.
NOTES
The flowers of X. amplexicaulis, with their broad and thick outer petals, are among the largest in the entire genus, and were the basis for the original placement of the plant in the genus Annona by Lamarck, and the recognition of section Pseudanona by Baillon and later a genus of the same name by Safford. The auriculate clasping leaf bases are unique in the genus and unusual among Annonaceae. Xylopia lamarckii, also endemic to Mauritius, has similar flowers but a distinctly petiolate leaf with a rounded base. Labels of the collections made by D. Lorence indicate that the branches are erect, forming a compact crown; such a growth habit is unusual within both the genus and family.
Two collections of Xylopia amplexicaulis in the Lamarck herbarium with handwritten labels state that they were collected by Commerson: one from Isle de France, the other from Madagascar. This agrees with the provenance information given in Lamarck’s protologue: “Cette plante croît à l’Isle de France & à Madagascar, où Commerson l’a observée”. Commerson apparently collected mostly around Taolagnaro (Fort Dauphin) during his brief visit to Madagascar (Morel 2012), and, as noted above, the plant has never been collected or reported from Madagascar subsequently. This provenance is regarded as a labeling error.
It is unclear whether the two locality labelings represent different collections, or the mis-labeling of some duplicates, but in either case, and to avoid future difficulties, a lectotype is designated above. Lamarck’s diagnosis states “Anona foliis cordato-oblongis acutis distichis amplexicaulibus”. The leaves of the specimen marked as collected from “isle de france” have distinctly acute apices in addition to the cordate bases, while the leaves of the specimen marked as collected from “ Madagascar “ have cordate bases but rounded apices. Lamarck’s description carefully describes the sepals and petals of the flowers, which are only present on the “ Madagascar ” specimen. This is also the more complete specimen, and is designated as the lectotype. There is uncertainty as to whether other collections are duplicates and thus isolectotypes, and they are therefore not listed as types.
description: Published as part of Johnson, David M. & Murray, Nancy A., 2020, A revision of Xylopia L. (Annonaceae): the species of Madagascar and the Mascarene islands, pp. 1-88 in Adansonia 42 (1) on pages 16-20, DOI: 10.5252/adansonia2020v42a1, http://zenodo.org/record/3877215