Physostigma

Taxonomy

Physostigma J.H. Balfour Trans. Roy. Soc. Edinburgh 22: 310. 1861.

Subfamily: Faboideae.
Phylogenetic Number: 3.10.52.
Tribe: Phaseoleae.
Subtribe: Phaseolinae.
Species Studied - Species in Genus: 4 studied; 4 in genus.

Description

Fruit: A legume; unilocular; 5–17 cm long; 0.5–5 cm wide; 2–9 times longer than wide to more than 9 times longer than wide; with deciduous androecial sheath; with deciduous corolla; with persistent calyx, or deciduous calyx; with calyx shorter than fruit; without orifice formed by curving of fruit or fruit segments; straight to curved (to slightly curved); not plicate; not twisted; asymmetrical, or symmetrical; fusiform, or linear, or falcate; with both sutures parallelly curved; not inflated; compressed; without beak, or with beak; straight, or declined, or hooked; with solid beak the same color and texture as fruit; long tapered at apex, or tapered at apex; aligned with longitudinal axis of fruit, or oblique 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; coriaceous to ligneous; seed chambers externally invisible, or visible; seed chambers with the raised seed chambers not torulose; margin not constricted, or constricted (slightly); margin constricted along both margins; margin without sulcus; margin plain, or embellished; margin with thickened sutural areas; wing(s) absent; stipitate, or nonstipitate; with the stipe 5–15 mm long; with all layers dehiscing; splitting along suture(s). Dehiscence of valves along both sutures; apical and down; active; with valves twisting. Replum invisible. Epicarp dull; monochrome; brown, or green; with surface texture uniform; glabrate, or pubescent and indurate; with hairs erect; with 1 type of pubescence; puberulent; with pubescence white; with pubescence uniformly distributed; with simple hairs; pliable; with hair bases swollen; eglandular; without spines; smooth, or not smooth; with elevated features; veined, or not veined; transversely veined relative to fruit length; not tuberculate; dotted; not exfoliating; without cracks; without embedded tissue, much thicker than epicarp, running from base to apex. Mesocarp present; thick, or thin; surface uniformly veined; 2-layered; with balsamic vesicles; without fibers; without reniform canals; with solid layer over solid layer; (sub-) ligneous. Endocarp present; visible; dull; opaque; monochrome; tan to white; cobwebby, scurfy, and smooth; without adhering pieces of testa; nonseptate; chartaceous, or osseous; not exfoliating; remaining fused to mesocarp and epicarp; without wings; entire. Seed(s) 2–9; length parallel with fruit length; neither overlapping nor touching; in 1 series. Funiculus 1–5 mm long (or longer); of 1 length only; flattened; triangular, or convoluted. Aril present; dry; when dry 2-lipped rim-aril (partial or whole); entire; without tongue (or flap) on lips of 2-lipped rim-aril; cream.

Seed: 5–48 mm long; 3.5–23 mm wide; 2–18.5 mm thick; not overgrown; not angular; asymmetrical; nearly elliptic, or irregular, or ovate; 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, or partially adhering to endocarp; free from endocarp; glossy to dull; not modified by a bloom; colored; monochrome; dark brown or brown; glabrous; smooth, or not smooth; with elevated features; reticulate to wrinkled; coriaceous. Pleurogram absent. Pseudopleurogram absent. Fracture lines absent. Rim absent. Wing(s) absent. Raphe visible, or not visible; from lens to base of seed and terminating; not bifurcating; color of testa, or lighter than testa; brown; raised, or recessed. Hilum present; visible, or partially concealed; concealed by funicular remnant and aril, or funicular remnant, or aril; with faboid split; with the lips of the faboid split the same color as the rest of the hilum; larger than punctiform; 1.4–41 mm long; with straight outline; linear; marginal according to radicle tip; flush, or recessed; within rim, or not within corona, halo, or rim; rim color of testa, or lighter than testa, or darker than testa. Lens discernible; 0.9–9 mm long; with margins straight, or curved; linear, or triangular; circular; not in groove of raphe, or in groove of raphe; confluent with hilum; flush, or recessed; same color as testa, or similar color as testa; darker than testa; brown; within rim, or not within corona, halo, or rim; rim color of testa. Endosperm present, or absent; thick; not pluglike and not resembling tip of radicle; covering entire embryo; adnate to embryo. 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; not concealing radicle; notched at radicle, or split over radicle; without lobes; with the interface division terminating at base of radicle; with margin(s) recessed; with 1 margin recessed, or both margins recessed; recessed on same side as radicle; yellow; inner face concave, or flat; glabrous on inner face. Embryonic axis right angled, or oblique; oblique to length of seed; without a joint evident between the radicle and the cotyledons. Radicle differentiated from cotyledon; bulbose, or triangular; lobe tip straight; oblique to cotyledons; centered between cotyledons; less than 1/2 length of cotyledons. Plumule rudimentary; glabrous.

Distribution

Tropical Africa.

Old World; Africa.

Generic Notes

Physostigma has been divided into subgenera, in part using seed characteristics (Gillett, 1966; Maréchal et al., 1978): subgenus Physostigma with 2–3 ovules per locule and the seed ca. 3 cm long and subgenus Taubertiophyton with 7–12 ovules per locule and the seed ca. 0.5 cm long.

Tribal Notes

Tribe Phaseoleae

Bruneau et al. (1995) carried out cladistic analyses of tribe Phaseoleae using chloroplast DNA restriction site data. Their results indicated that the tribe is not monophyletic and that the tribal delimitations between Phaseoleae and Desmodieae (11) and between Phaseoleae and Millettieae (7) are problematic.