Genistidium

Taxonomy

Genistidium I.M. Johnston J. Arnold Arbor. 22: 113. 15 Jan 1941.

Subfamily: Faboideae.
Phylogenetic Number: 3.8.11.
Tribe: Robinieae.
Group: Robinia.
Species Studied - Species in Genus: 1 studied; 1 in genus.

Description

Fruit: A legume; unilocular; 1.5–3.5 cm long; 0.4–0.7 cm wide; 0.25–0.27 cm thick; 2–9 times longer than wide; with persistent androecial sheath; with deciduous corolla; with persistent calyx; with calyx shorter than fruit; without orifice formed by curving of fruit or fruit segments; straight; not plicate; not twisted; symmetrical, or asymmetrical; linear (broadly); with both sutures nearly straight; not inflated; compressed; without beak; short tapered at apex; aligned with longitudinal axis of fruit; short tapered at base; aligned with longitudinal axis of fruit, or oblique with longitudinal axis of fruit (slightly); with the apex and base uniform in texture; coriaceous; seed chambers externally visible; seed chambers with the raised seed chambers not torulose; margin not constricted; margin without sulcus; margin plain; wing(s) absent; nonstipitate; with all layers dehiscing; splitting along suture(s). Dehiscence of valves along both sutures; apical and down; passive. Replum invisible. Epicarp dull; monochrome; tan; with surface texture uniform; pubescent and indurate; with hairs appressed; with 1 type of pubescence; with pubescence gray; with pubescence uniformly distributed; with simple hairs; pliable; with hair bases plain; eglandular; without spines; not smooth; with elevated features; not veined; not tuberculate; wrinkled; 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; nonseptate; chartaceous; not exfoliating; remaining fused to mesocarp and epicarp; without wings; entire. Seed(s) 1–3; length parallel with fruit length; neither overlapping nor touching; in 1 series. Funiculus of 1 length only; flattened; straight. Aril present; dry; when dry tongue-aril; entire; tan.

Seed: 4.2 mm long; 3.5 mm wide; 2 mm thick; not overgrown; not angular; symmetrical; circular (sub), or oblong; 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; not modified by a bloom; colored; mottled and streaked; with frequent mottles; with frequent streaks; brown (reddish); with black overlay; glabrous; smooth; coriaceous. Pleurogram absent. Pseudopleurogram absent. Fracture lines absent. Rim absent. Wing(s) absent. Raphe not visible. Hilum present; partially concealed; concealed by aril; with faboid split; with the lips of the faboid split the same color as the rest of the hilum; punctiform; marginal according to radicle tip; recessed; not within corona, halo, or rim. Lens discernible; 2 mm long; with margins straight; linear (with circular center); not in groove of raphe; adjacent to hilum; 0.5 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. 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; partially concealing radicle; notched at radicle; with lobes; with lobes not touching; without basal groin formed by lobes; with the interface division terminating at base of radicle; without margins recessed; brown (reddish); 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; linear; lobe tip straight; deflexed and parallel to cotyledon length; centered between cotyledons; less than 1/2 length of cotyledons. Plumule rudimentary; glabrous.

Distribution

United States (Texas: Brewster County) and Mexico (Coahuila and southern Nuevo León).

New World; United States to Mexico (Coahuila and Nuevo León, United States (Texas)).

Generic Notes

Lavin and Sousa (1995) monographed Genistidium. Only a limited number of seeds and fruits were available for study.

Tribal Notes

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).
 
 Fruit and seed:  G. dumosum  I.M. Johnson - fruit, valve, and seed.
Fruit and seed: G. dumosum I.M. Johnson - fruit, valve, and seed.
 Cotyledon, embryo, and testa:  G. germanica  C. Linnaeus - embryo, cotyledons, and testa SEMs.
Cotyledon, embryo, and testa: G. germanica C. Linnaeus - embryo, cotyledons, and testa SEMs.