Apios

Taxonomy

Apios P.C. Fabricius Nom. cons. Enum. 176. 1759.

Subfamily: Faboideae.
Phylogenetic Number: 3.10.07.
Tribe: Phaseoleae.
Subtribe: Erythrininae.
Species Studied - Species in Genus: 3 studied; 5 in genus.

Description

Fruit: A legume; unilocular; 5.8–14.5 cm long; 0.6–0.8 cm wide; 0.4–0.6 cm thick; more than 9 times longer than wide; with deciduous androecial sheath; with deciduous corolla; with persistent calyx; with calyx shorter than fruit; without orifice formed by curving of fruit or fruit segments; straight to curved (slightly); not plicate; not twisted; symmetrical to asymmetrical; linear (or nearly so), or moniliform (slightly); with both sutures parallelly curved; not inflated; terete; without beak, or with beak; straight, or coiled; with solid beak the same color and texture as fruit; long tapered at apex to tapered at apex; aligned with longitudinal axis of fruit to oblique with longitudinal axis of fruit (slightly); long tapered at base, or tapered at base; aligned with longitudinal axis of fruit; with the apex and base uniform in texture; chartaceous to coriaceous; seed chambers externally visible, or invisible; seed chambers with the raised seed chambers not torulose; margin not constricted; margin without sulcus; margin embellished; margin with 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, or green, or tan; with brown overlay (dark); mottling color combination constant; with mottling over seed chambers; with surface texture uniform; glabrous, or pubescent and indurate; with hairs appressed; with 1 type of pubescence; with pubescence golden; with pubescence uniformly distributed; with simple hairs; pliable; with hair bases plain; eglandular; without spines; not smooth; with elevated features (sometimes); veined; irregularly veined; not tuberculate; lenticular; 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 reniform canals; solid; coriaceous. Endocarp present; visible; dull; opaque; monochrome, or mottled; white; with mottling over seed chambers; with brown overlay; smooth; without adhering pieces of testa; septate; with septa thin (tissue paper-like), flexible; with septa eglandular; chartaceous; exfoliating in part; remaining fused to mesocarp and epicarp; without wings; entire. Seed(s) 3–18; length parallel with fruit length; neither overlapping nor touching; in 1 series. Funiculus 0.5–1.5 mm long; of 1 length only; flattened; curved, or triangular. Aril present; dry; when dry tongue-aril, or 2-lipped rim-aril; entire; covering less than 1/2 of seed; with tongues (or flap) on lips of 2-lipped rim-aril; with 1 tongue or flap on 1 lip of 2-lipped rim-aril, or 2 tongues or flaps, 1 on each lip of 2-lipped rim-aril; brown, or brown and tan.

Seed: 6.4–8.3 mm long; 4.5–5.4 mm wide; 2.8–6 mm thick; not overgrown; angular, or not angular; symmetrical, or asymmetrical; rectangular to ovate to obovate, or reniform; terete, or compressed; with surface smooth; without visible radicle and cotyledon lobes, or 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; brown to reddish brown; glabrous; smooth; chartaceous. Pleurogram absent. Pseudopleurogram absent. Fracture lines absent. Rim absent. Wing(s) absent. Raphe visible, or not visible; from hilum through lens to base of seed and terminating, or hilum to near base of seed and terminating, or hilum through lens and base of seed to point opposite hilum; not bifurcating; color of testa; raised, or raised and recessed. Hilum present; visible to partially concealed to fully 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; 1.2–1.5 mm long; with curved outline; elliptic; apical according to radicle tip but marginal according to seed length, or marginal according to radicle tip; recessed; within rim, or not within corona, halo, or rim; rim color darker than testa. Lens discernible, or not discernible; 0.5–1.2 mm long; with margins straight; linear; not in groove of raphe, or in groove of raphe; confluent with hilum; recessed, or mounded; same color as testa; within rim; rim color of 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, or not concealing radicle; split over radicle; without lobes; with the interface division terminating at base of radicle; without margins recessed; yellow, or tan; inner face flat, or concave; glabrous on inner face. Embryonic axis nearly straight, or oblique; oblique to length of seed, or perpendicular to length of seed; without a joint evident between the radicle and the cotyledons. Radicle differentiated from cotyledon; triangular, or linear; lobe tip straight, or curved; deflexed and parallel to cotyledon length, or deflexed and parallel to cotyledon width, or oblique to cotyledons; centered between cotyledons; less than 1/2 length of cotyledons. Plumule rudimentary, or moderately developed; glabrous.

Distribution

North America and Asia.

New World and Old World; Canada and United States; India, Indochina, and China.

New World crop.

Generic Notes

Lackey (1981) commented that this genus is very close to Cochlianthus (10.08) and that the two genera are possibly congeneric. Our fruit and seed data do not support Lackey's conclusions. Woods (1988) revised both Apios and Cochianthus, and his distributions and species counts were used. He concluded that the two genera are separate, but closely related. Apios americana produces sweet, starchy tubers which were eaten by North American native peoples (National Academy of Sciences 1979; Schery 1972). The tubers have a protein content of 17.5 percent.

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.