Pentalinon luteum aka Hammock Viper's Tail

Pentalinon luteum is an evergreen climber in the Apocynaceae family. Its common names include wild allamanda and hammock viper's-tail. Its native range runs from southern Florida through the Caribbean. It grows in a wet tropical climate. In Puerto Rico, it occurs in coastal woods and thickets. Young plants form shrubs with long, vine-like shoots. With time, they spread over nearby plants and other supports.

The stems twine around other plants as they climb. They can reach about 16 feet [5 metres] long. Garden height and width depend on the available support. Growth proceeds at a moderate rate. New stems are brown and have a medium thickness. The simple green leaves grow in opposite or nearly opposite pairs. Each oval leaf has smooth edges and pinnate veins. Leaves measure about 0.17–0.33 feet [0.05–0.10 metres] long. They stay green without a marked fall color change.

Yellow flowers open at the tips of the stems. Each bloom spans about 0.21 feet [0.064 metres]. Some flowers appear throughout the year, rather than in one brief season. The plant does not form a dense blanket of blooms. Its fruit is small in visual impact and adds little display. Flowers provide interest during winter as well as warmer months. The leaves remain on the plant through the year.

Full sun or partial shade gives the best flowering. Plants also grow in deep shade, but bloom less well. UF/IFAS lists USDA hardiness zones 10b through 11. The vine accepts sand, loam, and clay soils. It also tolerates both acid and alkaline conditions. Drought tolerance is high, while soil salt tolerance is moderate. Tolerance of salty air suits it to coastal gardens. Train it over an arbor or trellis, or against a support. Regular clipping can keep it as a shrub or low hedge. Cut long shoots back within the plant to encourage fuller growth.

This vigorous vine can spread beyond its allotted space. Pruning helps stop it from overwhelming a trellis. UF/IFAS reports few serious growth problems or lasting pest effects. Useful Tropical Plants lists no known food uses. It records traditional medicinal uses, including treatments for colic and skin complaints. These records do not establish safe or effective treatment. The same source reports its use as arrow poison. It also records use to stun fish, indicating a poisoning hazard.