The snail vine, snail bean, or caracol (Vigna caracalla (L.) Verdcourt) is a twining legume native to tropical South America. Linnaeus originally named the vine Phaseolus caracalla in 1753; Bernard Verdcourt moved the plant to the genus Vigna in 1970. Although known outside its habitat for over 250 years, this fascinating flower remains little used in gardens.

Under good conditions, the caracol [kar' ah kol, Spanish for snail) will grow six to eight meters (20-25 feet) in length. The fragrant flowers are papilionaceous, butterfly-like, and are borne in pendant clusters. They range from white to yellow with lavender wing petals to all pinkish-purple. The standard (upper petal) is ovate and the keel (lowest petal) is strongly curled like a snail's shell. The bases of the standard, keel, and wing petals are closely pressed together.

Caracol flowers produce abundant nectar, a lure for the correct-sized bee. The nectar is deep within the flower; the bee must push its way between the petals to reach its reward. As the keel petal is pushed downward, the stigma and stamens emerge from the tip of the keel. If the bee is carrying pollen from a previously visited flower, she will cross-pollinate the stigma. As the bee emerges from the nectar feast, she will pick up more pollen to carry to the next flower.

Once the bee flies off, the stigma and stamens retract into the keel for safe keeping from insects that may eat the pollen or damage the fragile stigma.

(Compiled from: "Vigna", Hortus Third, Staff L.H. Bailey Hortorium, New York State College of Agriculture and Life Sciences, Cornell University, Macmillan Publishing, 1976 and personal observations.)