Vigna unguiculata (L.) Walp. (cowpea, black-eyed pea)

V. sinensis (L.) Endl. ex Hassk.

Pl. 412 a, b; Map 1832

Plants annual (perennial herbs farther south), usually with stout taproots. Stems 50–300 cm long, variously trailing, climbing, and/or twining to erect and bushy, branched, unarmed, rounded or somewhat ridged, sometimes purplish-tinged, glabrous or with patches of short, stout, stiff hairs at the nodes. Leaves alternate, pinnately trifoliate, the petiole 6–11 cm long. Stipules 8–15 mm long, ovate, peltate, with a long, ovate to triangular lobe oriented downward below the attachment point, angled or tapered to a sharply pointed tip, strongly veined, more or less persistent; stipels 2–3 mm long, oblong-elliptic, persistent. Leaflets 4–12 cm long, 3–7 cm wide, ovate to broadly ovate, the terminal leaflet sometimes rhombic with a pair of shallow, blunt, spreading lobes toward the base, broadly angled or (if lobed) broadly tapered at the base, angled or slightly tapered to a sharply pointed tip, the lateral leaflets strongly asymmetric, broadly angled to truncate at the base, angled or slightly tapered to a sharply pointed tip, the margins entire, the surfaces glabrous, with 3 main veins from the base, but otherwise more or less pinnately veined. Terminal leaflet with the stalk 15–30 mm long, symmetric at the base; lateral leaflets with the stalk 2–4 mm long, oblique at the base. Inflorescences axillary, very short racemes or clusters, with 2–6 flowers, the stalk 50–200 mm long, the bracts 4–10 mm long, lanceolate, shed early, each flower with a stalk 1–2 mm long, the bractlets 3–5 mm long, oblong-obovate, glabrous, more or less persistent. Calyces glabrous (sometimes minutely hairy along the margins when young), the tube 3–5 mm long, bell-shaped, somewhat 2-lipped, the lobes 2.5–5.0 mm long, unequal, the upper 2 lobes fused to about their midpoints, the free portions triangular to broadly triangular, sharply pointed at their tips, the lower 3 lobes slightly shorter, similar, triangular, sharply pointed at their tips. Corollas papilionaceous, pink or purple (the tips of the wings and keel sometimes darker than the other portions), rarely greenish white (yellow elsewhere), the banner 14–18 mm long, 13–22 mm wide, the expanded portion curved or bent backward, broadly oblong-ovate to nearly circular, notched at the tip, with a slender longitudinal keel, lacking thickened areas toward the base, the wings 15–17 mm long, 7–8 mm wide, obliquely ovate to obovate, somewhat curved around the keel, the keel 15–17 mm long, 9–10 mm wide, boat-shaped, fused to about the tip, bent or curved upward abruptly near the midpoint, the tip bluntly to sharply pointed. Stamens 10, in 2 alternating, slightly shorter and longer series, 9 of the filaments fused and 1 free, the fused portion 11–12 mm long, bent upward at or near its tip, the free portion 6–7 mm long, the anthers small, attached above the base, yellow. Ovary 9–12 mm long, glabrous, the style 10–12 mm long, bent or curved upward abruptly toward the tip, somewhat flattened, densely short-hairy on the inner side, the stigma small, terminal. Fruits legumes, 10–20(–30) cm long, 5–10 mm wide, linear to narrowly oblong, short-tapered somewhat asymmetrically to a beak, slightly flattened, somewhat constricted between the seeds, straight or slightly curved, indehiscent or dehiscing tardily by 2 valves, green to straw-colored or reddish brown at maturity, sometimes with darker mottling, glabrous, with 8 to numerous seeds. Seeds 8–12 mm long, 6–8 mm wide, oblong to kidney-shaped in outline, somewhat flattened, the surface variously brown, green, cream-colored, or white, sometimes with darker mottling, smooth or finely wrinkled, dull or somewhat shiny, with a white, slightly raised aril often framed with black at maturity. 2n=22. August–September.

Introduced, uncommon and sporadic, mostly in the southeastern quarter of the state (probably a native of Africa, widely distributed in tropical and warm-temperate regions nearly worldwide, introduced in the eastern [mostly southeastern] U.S. west to Kansas and Texas). Banks of streams and rivers; also ditches, roadsides, and sandy, open, disturbed areas.

Vigna unguiculata is recognized by the coarse, bushy or twining habit, glabrous stems and leaves, large stipules with a basal lobe, flowers produced in small clusters at the end of an elongate stalk, and long, smooth legumes. It is one of the world’s important species of legume crops. It probably originated in sub-Saharan Africa and was disseminated to India and southern Europe very early (Smartt, 1990). Cowpeas were introduced into the United States in the 1700s (Wight, 1907) and became a major legume crop in the southern states. They thrive in hot, wet weather. When the peas are harvested very young, they are called cream peas. When harvested near maturity, after the dark patch around the hilum has developed, they are called black-eyed peas.

Verdcourt (1970b) treated V. unguiculata as a complex of five subspecies (three cultivated and two wild) differing in their degree of twining and quantitative details of the calyces and pods. In his classification, plants cultivated in the New World are all members of the widespread ssp. unguiculata.