Hammock viper’s-tail, wild allamanda

Vinca lutea Linnaeus, Cent. Pl. II, 12. 1756; Urechites andrewsii Small; U. luteus (Linnaeus) Britton; U. luteus var. sericeus R. W. Long; U. neriandrus Grisebach ex Miers; U. pinetorum Small

Woody vines, occasionally suf­frutescent at base. Stems gla­brous or densely pubescent. Leaves opposite; petiole 5–12 mm, pubescent; blade broadly obovate to oblong, 30–60 × 15–40 mm, membranous to subcoriaceous, base cuneate to acute or slightly cordate, margins often revolute, apex obtuse to acute or apiculate, surfaces pubescent abaxially. Peduncles 20–40 mm, sparsely pubescent. Pedicels 5–20 mm, sparsely pubescent. Flowers: calyx lobes linear-lanceolate, 7–12 mm, pubescent or glabrate; corolla glabrous abaxially, usually eglandular-pubescent adaxially, tube 6–15 × 2–3 mm, throat 15–35 × 8–12 mm, lobes spreading, obliquely rounded-obovate, 20–25 × 18–22 mm, adjacent lobes overlapping for 1/2+ of their length from base. Follicles 120–180 × 4–5 mm. Seeds 10–12 × 1 mm not including beak, beak ± as long as body of seed. 2n = 12.

Flowering and fruiting year-round. Roadside thickets, pine flatwoods, coastal hammocks, mangrove swamps, beach dunes; 0–10 m; Fla.; West Indies; South America (Colombia).

In Florida, Pentalinon luteum occurs sporadically from St. Lucie and Lee counties southward.

G. E. Burrows and R. J. Tyrl (2013) reported that in Cuba, where Pentalinon luteum is locally abundant, cattle may suffer hemorrhagic diarrhea and sudden death from ventricular fibrillation upon ingestion of the plants.