Pachyrhizus

Taxonomy

Pachyrhizus A. Richard ex A.P. de Candolle Nom. cons. Prodr. 2: 402. Nov (med.) 1825.

Subfamily: Faboideae.
Phylogenetic Number: 3.10.46.
Tribe: Phaseoleae.
Subtribe: Glycininae.
Species Studied - Species in Genus: 4 studied; 5 in genus.

Description

Fruit: A legume; unilocular; 6–25.5 cm long; 0.8–2.8 cm wide; 0.3–0.6 cm thick; 2–9 times longer than wide, or more than 9 times longer than wide; with persistent androecial sheath, or 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; slightly curved; not plicate; not twisted; asymmetrical, or symmetrical; linear; with both sutures parallelly curved; not inflated; compressed to terete; without beak; tapered at apex; aligned with longitudinal axis of fruit, or oblique with longitudinal axis of fruit; long tapered at base, or tapered at base; aligned with longitudinal axis of fruit; 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, or embellished; margin with flange(s) (narrow), or thickened sutural areas; 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 black overlay, or brown overlay, or gray overlay; mottling color combination variable; with surface texture uniform; pubescent and indurate, or pubescent but soon deciduous; with hairs erect, or appressed; with 1 type of pubescence; tomentose, or sericeous (and appressed); with pubescence golden; with pubescence uniformly distributed; with simple hairs; pliable; with hair bases plain; eglandular; without spines; smooth, or not smooth; with recessed features; not veined; not tuberculate; grooved; not exfoliating; with cracks, or without cracks; cracking oblique to fruit length; without embedded tissue, much thicker than epicarp, running from base to apex. Mesocarp present; thin; surface not veined; 1-layered; without balsamic vesicles; without reniform canals; solid; coriaceous. Endocarp present; visible; dull; opaque; monochrome; tan; smooth and scurfy; without adhering pieces of testa; septate; with septa thicker than paper, firm; with septa eglandular; chartaceous; exfoliating in part; remaining fused to mesocarp and epicarp; without wings; entire. Seed(s) 4–12(–18); length transverse to fruit length, or parallel with fruit length; neither overlapping nor touching; in 1 series. Funiculus 1–2 mm long; of 1 length only; flattened; triangular. Aril present; dry; when dry tongue-aril, or 2-lipped rim-aril; entire; covering less than 1/2 of seed; cream.

Seed: 9.5–15.5 mm long; 9–14.5 mm wide; 4.5–6.5 mm thick; not overgrown; angular, or not angular; symmetrical, or asymmetrical; D-shaped, or quadrangular, or rectangular, or reniform; 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; dull; not modified by a bloom; colored; monochrome; brown to reddish brown, or green (olive), or red (brownish), or black; glabrous; smooth, or not smooth; with recessed features; pitted with small separate pits; coriaceous. Pleurogram absent. Pseudopleurogram absent. Fracture lines absent, or present; transverse. 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; larger than punctiform; 3.5–4 mm long; with curved outline; elliptic; apical at apex of radicle tip; recessed; within rim; rim color of testa. Lens discernible; 2.3–2.5 mm long; with margins straight; linear; not in groove of raphe; confluent with hilum; recessed; dissimilar color from testa; black; within rim; rim color of testa, or darker than testa. 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; partially concealing radicle; notched at radicle; without lobes; with the interface division terminating at base of radicle; without margins recessed; white to tan; inner face flat; glabrous on inner face. Embryonic axis straight, or oblique; parallel to length of seed; without a joint evident between the radicle and the cotyledons. Radicle differentiated from cotyledon; bulbose; lobe tip straight, or curved (slightly); straight with embryonic axis; centered between cotyledons; less than 1/2 length of cotyledons. Plumule rudimentary to moderately developed; glabrous.

Distribution

Neotropics, And widely cultivated.

New World; Mexico to West Indies to Central America to South America; Brazil and Argentina.

Worldwide crop.

Generic Notes

SØrensen (1988) monographed the genus, and our species count is based on his treatment, not Lackey (1981).

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.