Strophostyles helvola (L.) Elliott, trailing wild bean, ameriquebean. Perennial vine, twining on itself and climbing on neighboring plants and other supports; shoots with only cauline leaves.
Stems ridged and subtly angled, to 2 mm diameter, internodes long and to 110 mm long, aging red–purple starting along ridges on exposed side, pilose.
Leaves helically alternate, pinnately 3–foliolate, petiolate with pulvinus, with stipules; stipules 2, attached to stem and base of pulvinus, lanceolate–triangular, ca. 3.5 × 1 mm, green, ridged on lower surface, parallel–veined, appressed short–ciliate on margins; petiole to 55 mm long, pulvinus ca. 1.5 mm long, axis above pulvinus channeled and 2–ridged, ± 1 mm diameter, ridges often red–purple, pilose to strigose; rachis channeled, to 8 mm long, pilose; stipel 1 at petiolule of each lateral leaflet and 2 at petiolule of terminal leaflet, acute, 1—1.3 × 0.6—0.7 mm, parallel–veined, with inconspicuous glands on margins; petiolule = pulvinus, pilose with hairs angled downward from lateral leaflets; blades of leaflets ovate to mitten–shaped and shallowly to deeply 2—3–lobed with lateral lobes below midpoint, to 50 × 37 mm, central lobe often wider above midpoint (obovate), lateral leaflets asymmetric at base, lobes entire, obtuse with short point at tip, 3–veined at base with principal veins raised on lower surface, upper surface short–strigose but strigose along principal veins, lower surface strigose.
Inflorescence raceme, axillary, mostly with 10+ flowers, flowers helically alternate, bracteate; peduncle strongly ridged, at anthesis 160—225 mm long and >> leaf, with disclike pulvinus at base, mostly strigose with downward–pointing hairs (pilose); rachis ridged, each ridge descending from bractlet, short–strigose; bractlet subtending base of pedicel awl–shaped, 2—2.4 mm long, pale green, sparsely short–strigose and minutely ciliate on narrow membranous margins; pedicel ca. 1 mm long, with short hairs, at top with 2 opposite bracteoles oriented 90° from bractlet, bracteoles lanceolate with swollen base, 3.5—3.7 × 1—1.2 mm, 7(9)–veined, with several short–strigose hairs, persistent in fruit.
Flower bisexual, bilateral, pealike (papilionaceous), ca. 10 mm across; nectary on receptacle surrounding ovary, producing abundant nectar; calyx 2–lipped, appearing 4–lobed, ca. 5 mm long; tube bell–shaped, 2—2.3 × 2.3—2.5 mm, sparsely short–hairy to glabrate; upper lip (= 2 lobes) broadly ovate, ca. 2 × 3.5 mm, purplish; lower lip 3–lobed, mostly green, lower lobe acuminate, 2 mm long, short–hairy, lateral lobes ± deltate, 1.5 mm, short–hairy; petals 5, clawed, glabrous; banner with short–claw, limb spreading, roundish with short notch at top, 11—12 × 11—12 mm, cream–colored to midpoint and pink–purple above midpoint (fading quickly when picked), having a purple crescent several mm above the claw and above that faint radiating lines, at base of limb with a pair of lobes curved upward; wings 2, oriented forward beside the keel but not attached, claw linear, 2 mm long, white, limbs ± oblong, ca. 8 × 3 mm, mostly white but pink–purple at tips; keel of 2 petals fused most of length, claws linear, 2 mm long, white, limbs fused on lower side from claw to tip and on the upper side ca. 2/3 with only ca. 3 mm open from claw to exposed stamens, wider lower portion ca. 6 × 6 mm, white, upper portion twisted and curved backward (partially coiled), white to deep purple on coil; stamens 10, diadelphous (9 filaments fused and 1 free), fully enclosed by keel; filament sheet somewhat sigmoid (corresponding to coiled keel), ca. 8 mm long, white, flared upward and bent 90° approaching free portions 5—6 mm long; anthers dorsifixed, dithecal, 0.6—0.75 mm, light yellow, longitudinally dehiscent; pollen light yellow; pistil 1, ca. 15 mm long, curved to conform to keel and fully enclosed within keel; ovary superior, cylindric and crescent–shaped, ca. 5 mm long, white, sparsely short–hairy, 1–chambered with to 10 ovules attached to upper side; style curved and compressed side–to–side, white at base to greenish and short–hairy above midpoint, having a dense tuft of longer hairs around terminal green stigma.
Fruit pod (legume), often 8—9–seeded, dehiscent by 2 valves twisting 180—540°, before splitting cylindric with a pointed beak (style), 45—100 × 5—5.5 × 5—5.5 mm, tannish brown, with raised veins, slightly bulging at seeds, sparsely short–strigose with hairs pointing toward tip.
Seed oblong, 4.5—6 × 3 × 2.5—4 mm, black to reddish black with linear whitish hilum, smooth or sometimes with crusty surface material; hilum ca. 3 mm long (> 1/2 length of seed) with small bump at each end of hilum.
A. C. Gibson