Oxystigma

Taxonomy

Oxystigma H.A.T. Harms In Engler et Prantl, Nat. Pflanzenfam. Nachtr. (2–4): 195. Oct 1897.

Subfamily: Caesalpinioideae.
Phylogenetic Number: 1.4.26.
Tribe: Detarieae.
Group: Crudia.
Species Studied - Species in Genus: 5 studied; 5 in genus.

Description

Fruit: A legume; unilocular; 3.5–13 cm long; 2.2–8 cm wide; 0.5–4 cm thick; length less than twice as long as width to 2–9 times longer than wide; with deciduous androecial sheath; with deciduous corolla; with deciduous calyx; without orifice formed by curving of fruit or fruit segments; straight; not plicate; not twisted (but occasionally bent); symmetrical, or asymmetrical; nearly circular, or oblong, or C-shaped, or irregular; with both sutures parallelly curved, or both sutures unequally curved; not inflated; compressed; without beak; tapered at apex to rounded at apex; aligned with longitudinal axis of fruit; tapered at base to rounded at base; aligned with longitudinal axis of fruit; with the apex and base uniform in texture; ligneous; seed chambers externally invisible; margin not constricted; margin without sulcus; margin embellished; margin with wing(s); wing(s) present, or absent; wing(s) 0.1–9 mm wide; wing(s) samaroid; wing(s) basal (seed chamber apical, wing basal); nonstipitate; indehiscent. Replum invisible. Epicarp dull; monochrome; blackish to reddish brown; with surface texture uniform; glabrous; eglandular; without spines; not smooth; with elevated features; usually veined, or not veined; longitudinally veined relative to fruit length; not tuberculate; not exfoliating; without cracks; without embedded tissue, much thicker than epicarp, running from base to apex. Mesocarp present; surface not veined; 2-layered; without balsamic vesicles; without fibers; without reniform canals; with outer layer drupaceous when fresh, when dry soft or spongy layer over solid layer; ligneous. Endocarp present; visible; glossy; opaque; monochrome; dark reddish brown; without adhering pieces of testa; nonseptate; not exfoliating; remaining fused to mesocarp and epicarp; entire. Seed(s) 1; length parallel with fruit length. Funiculus 0.1–0.9 mm long; of 1 length only; thick; straight. Aril absent.

Seed: 20–50 mm long; 20–40 mm wide; 15–30 mm thick; not overgrown; not angular; symmetrical; nearly cordate, or oblong; nearly terete to compressed; with surface smooth; without visible radicle and cotyledon lobes; without hilar sinus; without umbo on seed faces; without medial ridge on each face. Cuticle not exfoliating; not inflated; not wrinkled. Testa present; without pieces of adhering epicarp; not adhering to endocarp; free from endocarp; glossy to dull; not modified by a bloom; colored; monochrome; reddish brown; glabrous; not smooth; with recessed features; pitted with small separate pits; chartaceous. Pleurogram absent. Pseudopleurogram absent. Fracture lines absent. Rim absent. Wing(s) absent. Raphe not visible. Hilum present; visible; without faboid split; punctiform; apical at apex of radicle tip; flush; not within corona, halo, or rim. Lens not discernible. Endosperm absent. Cotyledons smooth; both outer faces convex; both the same thickness; both more or less of equal length; not folded; margin entire 180 degrees from base of radicle; similar at apex; completely concealing radicle; entire over radicle; with the interface division terminating at base of radicle; without margins recessed; inner face flat; glabrous on inner face. Embryonic axis straight; parallel to length of seed; without a joint evident between the radicle and the cotyledons. Radicle differentiated from cotyledon; centered between cotyledons. Plumule glabrous.

Distribution

Guineo-Congolian forest and Tanzania.

Old World; Africa (Guineo-Congolian forest and Tanzania).

Generic Notes

LÉonard et al. (1952, fig. 30) showed fruit shape variation in O. buchholzii, O. gilbertii, and O. oxyphyllum. Seeds germinate within the fruit because the cotyledons are locked in place by intrusion of the endocarp. This causes the foveolate appearance of the seed and the ruminate cotyledons. Brenan (1967) noted that Oxystigma is not or scarcely distinct from Kingiodendron (4.26), and seed characters confirm this statement.

Tribal Notes

Tribe Detarieae

Bruneau et al. (2000) carried out extensive phylogenetic analyses of tribes Amherstieae and Detarieae. They concluded that they form a single monophyletic group. Therefore, they supported Polhill's (1995a, 1995b) decision to unite the two tribes.