Discolobium

Taxonomy

Discolobium G. Bentham Commentat. Legum. Gener. 41. Jun 1837.

Subfamily: Faboideae.
Phylogenetic Number: 3.14.17.
Tribe: Aeschynomeneae.
Subtribe: Discolobiinae.
Species Studied - Species in Genus: 3 studied; 8 in genus.

Description

Fruit: A legume; unilocular; 2.7–3.7 cm long; 0.8–1.2 cm wide; 0.07–0.09 cm thick; 2–9 times longer than wide; with persistent androecial sheath, or deciduous androecial sheath; with deciduous corolla; with persistent calyx; with calyx shorter than fruit; without orifice formed by curving of fruit or fruit segments (because of the upper and lower coils arising from a twisted suture); 1-coiled to 3-coiled (when single coiled, with one major central coil with upper and lower much smaller, sterile coils); not plicate; twisted (top and bottom coils twisted when compared to center coil); symmetrical; circular; not inflated; flattened; without beak; rounded at apex (with persistent long, thick style); oblique with longitudinal axis of fruit; rounded at base; right angled 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 embellished; margin with wing(s); wing(s) present; wing(s) 1 (per coil); wing(s) 3–4 mm wide; wing(s) sutural; wing(s) on 1 suture; nonstipitate; indehiscent. Replum invisible. Epicarp glossy (nearly); monochrome; brown, or red (dish), or tan; with surface texture uniform; glabrous, or pubescent but soon deciduous; with hairs erect; with 1 type of pubescence; puberulent; with pubescence gray; with pubescence uniformly distributed; with simple hairs; pliable; with hair bases plain; eglandular; with spines (short and widely spaced on valves of D. pulchellum G. Bentham); not smooth; with elevated features; veined; reticulately veined; tuberculate, or not tuberculate; with solid tubercles on each valve; tuberculate; not exfoliating; without cracks; without embedded tissue, much thicker than epicarp, running from base to apex. Mesocarp absent. Endocarp present; visible; dull; opaque; monochrome; tan; spongy; without adhering pieces of testa; nonseptate; chartaceous; not exfoliating; remaining fused to epicarp; with wing(s) extending into epicarp; entire. Seed(s) 1; length parallel with fruit length. Funiculus thick; straight. Aril absent.

Seed: 8 mm long; 5 mm wide; 0.4 mm thick; not overgrown; not angular; asymmetrical; reniform (to lunate); flattened; with 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; dull; not modified by a bloom; colored; monochrome; reddish brown; not smooth; with elevated features; wrinkled; chartaceous. Pleurogram absent. Pseudopleurogram absent. Fracture lines absent. Rim absent. Raphe not visible. Hilum present; fully concealed; concealed by funiculus; without faboid split; larger than punctiform; 1 mm long; with curved outline; elliptic; marginal according to radicle tip, or between cotyledon and radicle lobe; flush; not within corona, halo, or rim. Lens not discernible. Endosperm absent. 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 notched at radicle; without lobes; with the interface division terminating at base of radicle; without margins recessed; red; 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 curved; oblique to cotyledons; centered between cotyledons; less than 1/2 length of cotyledons. Plumule rudimentary; glabrous.

Distribution

Brazil, Paraguay, and Argentina.

New World; South America (Brazil, Paraguay, Argentina); Argentina and Brazil.

Generic Notes

Burkart (1952) monographed the four species in Argentina and provided excellent seed and fruit illustrations of Discolobium psoraleifolium. The curiously formed fruit of Discolobium are unusual, though not as unique as Eligmocarpus cynometroides Capuron (Caesalpinioideae: Cassieae) (Gunn, 1991). The Discolobium fruit is composed of three whorls: Upper and lower smaller in diameter and sterile and the middle whorl larger in diameter and one-seeded (figure B). This arrangement indicates wind dispersal of the seeds in the indehiscent fruits.

Tribal Notes

Tribe Aeschynomeneae

Rudd (1981a) recognized four subtribes of Aeschynomeneae: Ormocarpinae V.E. Rudd (genera 3.14.01–3.14.08), Aeschynomeninae (genera 3.14.09–3.14.16), Discolobinae (A.E. Burkart) V.E. Rudd (genus 3.14.17: Discolobium), Poiretiinae (A.E. Burkart) V.E. Rudd (genera 3.14.18–3.14.21), and Stylosanthinae (G. Bentham) V.E. Rudd (genera 3.14.22–13.4.26). Tribal and subtribal placement of Diphysa is based on Lavin (1987; Polhill, 1994a, 1994b), and not on Polhill and Sousa (1981), who placed Diphysa in Robinieae. Bailey et al. (1997), using the chloroplast rpl2 intron and ORF184, suggested that Brya (11.01), Cranocarpus (11.02), Phylacium (11.22), and Neocollettia (11.26) are not members of Desmodieae (11) and that they probably belong in Aeschynomeneae.