Subfamily: Faboideae.
Phylogenetic Number: 3.8.07.
Tribe: Robinieae.
Group: Robinia.
Species Studied - Species in Genus: 4 studied; 4 in genus.
Fruit: A legumelegume:
usually dry, dehiscent fruit derived from a single carpel that opens along two longitudinal sutures
; unilocular; 4.5–10 cm long; 0.8–1 cm wide; 0.2 cm thick; 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, or curved (slightly); not plicate; not twisted; symmetrical, or asymmetrical; linear; with both sutures nearly straight; not inflated; flattened, or compressed; without beak, or with beak; with solid beak the same color and texture as fruit; tapered at apex; aligned with longitudinal axis of fruit; short tapered at base; aligned with longitudinal axis of fruit; with the apex and base uniform in texture; coriaceous; seed chambers externally invisible, or visible; seed chambers with the raised seed chambers not torulose; margin not constricted, or constricted; margin constricted along both margins; margin without sulcus; margin plain, or embellished; margin with wing(s); wing(s) absent, or present (occasionally); wing(s) 1; wing(s) 0.1–0.2 mm wide; wing(s) sutural; wing(s) on 1 suture (upper); substipitate; with all layers dehiscing; splitting along suture(s). Dehiscence of valves along both sutures (lower suture first); apical and down; active; with valves twisting. Replum invisible. Epicarp dull; monochrome, or multicolored; streaked; brown (reddish); with red overlay; with surface texture uniform; glabrous, or pubescent and indurate; with hairs erect; with 1 type of pubescence; puberulent; with pubescence gray; with pubescence uniformly distributed; with simple hairs; pliable; with hair bases plain; glandular; with glandular hairs; with spines; not smooth; with elevated features, or recessed features; veined, or not veined; reticulately veined (faintly and incompletely); tuberculate; warty, or tuberculate; slitted obliquely (minute); not exfoliating; without cracks; without embedded tissue, much thicker than epicarp, running from base to apex. Mesocarp present; thin; surface not veined; 1-layered; without balsamic vesicles; without fibers; without reniform canals; solid; coriaceous. Endocarp present; visible; dull; opaque; monochrome; tan; smooth; without adhering pieces of testa; septate, or nonseptate; with septa thicker than paper, firm; with septa eglandular; chartaceous; not exfoliating; remaining fused to mesocarp and epicarp; without wings, or with wing(s) extending into epicarp (occasionally); entire. Seed(s) 2–13; length transverse to fruit length; neither overlapping nor touching; in 1 series. Funiculus 0.5–1.5 mm long; of 1 length only; thick; straight, or curved (near hilum). Aril present; dry; when dry rim-aril; entire; tan.
Seed: 4–6 mm long; 3–3.5 mm wide; 1.7–2 mm thick; not overgrown; not angular; asymmetrical; reniform, or ovate; compressed; with surface smooth; with visible radicle and cotyledon lobes, or without visible radicle and cotyledon lobes; without external groove between 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, or dull; not modified by a bloom; colored; monochrome, or mottled and streaked; with frequent mottles; with frequent streaks; brown (reddish), or black; with black overlay; glabrous; smooth; coriaceous. Pleurogram absent. Pseudopleurogram absent. Fracture lines absent. Rim absent. Wing(s) absent. Raphe visible; from hilum through lens to base of seed and terminating; not bifurcating; color of testa, or lighter than testa; brown (reddish); flush. Hilum present; visible, or fully concealed; concealed by funiculus; with faboid split; with the lips of the faboid split the same color as the rest of the hilum; larger than punctiform; 0.5–0.8 mm long; with curved outline; circular; marginal according to radicle tip; recessed; within halo; halo lighter than testa. Lens discernible; 0.7–0.8 mm long; with margins curved; circular, or elliptic; not in groove of raphe; adjacent to hilum; 0.8 mm from hilum; mounded; similar color as testa; darker than testa; brown (reddish); not within corona, halo, or rim. Endosperm present; thin; not pluglike and not resembling tip of radicle; covering entire embryo; adnate to testa, or 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; split over radicle; with lobes; without basal groin formed by lobes; with the interface division terminating at base of radicle; without margins recessed; tan; inner face flat; glabrous on inner face. Embryonic axis deflexed; oblique to length of seed; without a joint evident between the radicle and the cotyledons. Radicle differentiated from cotyledon; bulbose; lobe tip straight; deflexed and parallel to cotyledon length; centered between cotyledons; less than 1/2 length of cotyledons. Plumule rudimentary, or moderately developed; glabrous.
United States and Mexico.
New World; United States to Mexico.
Isely and Peabody (1984) and Lavin and Sousa (1995) recognized only four species, the count we used, not the Polhill and Sousa (1981) number of 10(-20) species with this caveat: "Perhaps only four or five basic species.".
Tribe Robinieae
The genera, generic groups, and related data follow the tribal treatment of Lavin and Sousa (1995; Polhill, 1994a, 1994b), not Polhill and Sousa (1981).