Sphenostylis

Taxonomy

Sphenostylis E.H.F. Meyer Comment. Pl. Africae Austr. 148. 14 Feb-5 Jun 1836.

Subfamily: Faboideae.
Phylogenetic Number: 3.10.57.
Tribe: Phaseoleae.
Subtribe: Phaseolinae.
Species Studied - Species in Genus: 4 studied; 7 in genus.

Description

Fruit: A legumelegume:
usually dry, dehiscent fruit derived from a single carpel that opens along two longitudinal sutures
; unilocular; 8.5–15 cm long; 0.5–0.9 cm wide; more than 9 times longer than wide; with deciduous androecial sheath; with deciduous corolla; with persistent calyx; with calyx shorter than fruit; without orifice formed by curving of fruit or fruit segments; straight, or curved (slightly); not plicate; not twisted; symmetrical, or asymmetrical; linear, or falcate; with both sutures parallelly curved; not inflated; flattened to compressed; without beak, or with beak; straight to declined; with solid beak the same color and texture as fruit; long tapered at apex to tapered at apex; aligned with longitudinal axis of fruit, or oblique with longitudinal axis of fruit; short tapered at base to rounded at base; aligned with longitudinal axis of fruit; with the apex and base uniform in texture; coriaceous; seed chambers externally invisible; margin not constricted; margin without sulcus; margin plain, or embellished; margin with thickened sutural areas, or ridge(s) (slightly); wing(s) absent; nonstipitate; 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, or multicolored; mottled; brown; with brown overlay; mottling color combination constant; with mottling over seed chambers; with surface texture uniform; glabrous, or pubescent but soon deciduous; with hairs appressed; with 1 type of pubescence; with pubescence golden; with pubescence uniformly distributed; with simple hairs; pliable; with hair bases swollen; eglandular; without spines; not smooth; with elevated features; not veined; not tuberculate; dotted; not exfoliating; without cracks; without embedded tissue, much thicker than epicarp, running from base to apex. Mesocarp present; thick; surface not veined; 2-layered; without balsamic vesicles; without fibers; without reniform canals; with spongy layer over solid layer; coriaceous. Endocarp present; visible; dull; opaque; monochrome, or mottled; tan; with mottling more or less uniform (dark); with brown overlay; cobwebby and scurfy; without adhering pieces of testa; septate; with septa thin (tissue paper-like), flexible to thicker than paper, firm; with septa eglandular; chartaceous; exfoliating in part; remaining fused to mesocarp and epicarp; without wings; entire. Seed(s) 5–15; length parallel with fruit length; neither overlapping nor touching; in 1 series. Funiculus 0.1–0.6 mm long; of 1 length only; thick; straight. Aril present; dry; when dry rim-aril and tongue-aril, or hippocrepiform rim-aril; entire; cream.

Seed: 3.5–12.2 mm long; 3–6.5 mm wide; 2–6.5 mm thick; not overgrown; angular, or not angular; symmetrical; circular, or D-shaped, or oblong; terete, or 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; dull; not modified by a bloom; colored; monochrome, or mottled; with infrequent mottles; black to brown (or dark brown); with black overlay, or brown overlay (darker); glabrous; smooth, or not smooth; with elevated features; reticulate, or rugose, or papillate; chartaceous. Pleurogram absent. Pseudopleurogram absent. Fracture lines absent. Rim absent. Wing(s) absent. Raphe visible; from hilum through lens and base of seed to point opposite hilum; not bifurcating; color of testa, or lighter than testa; brown; raised. Hilum present; partially concealed, or fully concealed; concealed by aril; with faboid split; with the lips of the faboid split the same color as the rest of the hilum; larger than punctiform; 1–3 mm long; with curved outline; elliptic; apical according to radicle tip but marginal according to seed length; flush; not within corona, halo, or rim, or within rim; rim color of testa. Lens discernible; 0.5–2.2 mm long; with margins straight, or curved; linear; circular, or elliptic; not in groove of raphe; confluent with hilum; mounded, or flush, or recessed; same color as testa; dark brown; not within corona, halo, or rim. Endosperm present, or absent; trace; not pluglike and not resembling tip of radicle; restricted to region of embryo; adnate to testa. 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; without lobes; with the interface division terminating at base of radicle; without margins recessed; yellow, or pink; inner face flat; glabrous on inner face. Embryonic axis straight, or oblique, or right angled; perpendicular 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, or deflexed and parallel to cotyledon width; centered between cotyledons; less than 1/2 length of cotyledons. Plumule well developed; glabrous.

Distribution

Tropical and southern Africa.

Old World; Africa and India.

Generic Notes

Potter and Doyle (1994) developed phylogenetic hypotheses for Sphenostylis, and altered the generic circumscription accordingly. Their species count and distribution were used. Sphenostylis stenocarpa, the African yam bean, has distinct wild and cultivated forms (Potter, 1992). The cultivated type has larger fruit with delayed dehiscence and larger seeds with smooth testa. Wild type seeds are smaller with black waxy elaborationms on the testa, also found in other species.

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.