Orbexilum

Taxonomy

Orbexilum C.S. Rafinesque-Schmaltz Atlantic J. 145. Oct-Dec 1832.

Subfamily: Faboideae.
Phylogenetic Number: 3.12.07.
Tribe: Psoraleeae.
Species Studied - Species in Genus: 6 studied; 8 in genus.

Description

Fruit: A legume; unilocular; 0.3–1.2 cm long; 0.3–0.65 cm wide; 0.3 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 persistent calyx, or deciduous calyx; with calyx shorter than fruit; without orifice formed by curving of fruit or fruit segments; straight; not plicate; not twisted; asymmetrical, or symmetrical; circular, or obovate; with 1 straight and 1 curved suture; widest near middle or D-shaped; not inflated; compressed; without beak, or with beak; straight; with solid beak the same color and texture as fruit; short tapered at apex to rounded at apex; aligned with longitudinal axis of fruit (with 3–4 mm long beak), or right-angled with longitudinal axis of fruit; short tapered at base to rounded at base; aligned with longitudinal axis of fruit to oblique 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; wing(s) absent; nonstipitate; indehiscent. Replum invisible. Epicarp dull; monochrome; brownish black, or brown, or green; with surface texture uniform; glabrous to glabrate to 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, or eglandular; with glandular dots; without spines; not smooth; with elevated features; veined; obliquely veined relative to fruit length, or reticulately veined; not tuberculate; papillose, or rugose; not exfoliating; without cracks; without embedded tissue, much thicker than epicarp, running from base to apex. Mesocarp present; thin; 1-layered; without balsamic vesicles; without fibers; without reniform canals; solid; coriaceous. Endocarp present; visible; dull; opaque; monochrome; brown; smooth; without adhering pieces of testa; nonseptate; chartaceous; not exfoliating; remaining fused to mesocarp and epicarp; without wings; entire. Seed(s) 1; length parallel with fruit length. Funiculus less than 1 mm long; thick; straight. Aril absent.

Seed: 2–7 mm long; 2–4 mm wide; 2.5 mm thick; not overgrown; not angular; asymmetrical; ovate, or reniform; compressed to terete (nearly); 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; dull; not modified by a bloom; colored; monochrome; black, or brown (reddish); glabrous; smooth; coriaceous. Pleurogram absent. Pseudopleurogram absent. Fracture lines absent. Rim absent. Raphe not visible. Hilum present; visible; with faboid split; with the lips of the faboid split the same color as the rest of the hilum; larger than punctiform; 0.6 mm long; with curved outline; circular; marginal according to radicle tip; flush; not within corona, halo, or rim. Lens not discernible. Endosperm present; thin; not pluglike and not resembling tip of radicle; covering entire 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; entire over radicle, or split over radicle; without lobes, or with lobes; with the interface division terminating in radicle tissue; without margins recessed; tan; inner face flat; glabrous on inner face. Embryonic axis deflexed; parallel to length of seed; without a joint evident between the radicle and the cotyledons. Radicle differentiated from cotyledon; linear; deflexed and parallel to cotyledon length; centered between cotyledons; less than 1/2 length of cotyledons. Plumule rudimentary; glabrous.

Distribution

North America and Mexico.

New World; United States to Mexico.

Generic Notes

Stirton (1981) noted that "Orbexilum is all that remains of Psoralea s.l." when other segregate genera including Psoralea s.s. (11.08) are removed. "Furthermore, Orbexilum is clearly an unsatisfactory assemblage of plants." The species count and distribution are based on Grimes (1990) who noted "Orbexilum is easily distinguished from all other Psoraleeae by its rugose fruits." Also, he classified fruits as rugose-ribbed, but in O. onobrychis (T. Nuttall) P.A. Rydberg fruits are papillate.

Tribal Notes

Tribe Psoraleeae

Stirton (1981) illustrated seeds and fruits of Amorpheae and Psoraleeae. Since Isely (1962) monographed the tribe for north-central United States the spelling of the tribe name has changed as well as the genera recognized in the tribe. Amorpha (6.04), Dalea (6.08) and Petalostemon A. Michaux (now part of Dalea) are now in the Amphoreae (6), and species in the remaining genus, Psoralea (12.09), have been assigned to several genera treated here. Grimes (1990) noted that this tribe "has been described as having indehiscent fruits. However, in many North American species the fruit is secondarily dehiscent (that is, not along sutures) by transverse rupture of the pod." This technically is not dehiscence.