Tendrils are cylindrical coiling organs used as a climbing and support mechanism by a number of vines. The morphological origin of tendrils varies, and may be the leaf, shoot, or inflorescence rachis, depending on the species. Thus tendrils are a good example of convergent evolution. Coral vine (Antigonon leptopus), a native of Mexico and Central America, possesses tendrils on the axillary inflorescences. Typically, bract-subtended flowers develop on the basal portion of the inflorescence. A transition zone consisting of one or two nodes with tendril-subtended flowers occurs in the middle portion of the inflorescence, and the inflorescence is terminated by three "empty" tendrils. Tendrils are initiated in the same manner as a leaf or a bract, but they remain cylindrical except for what appears to be a rudimentary blade at the tip. Developmental and histological evidence indicates that the tendril in this species is a leaf homologue. The initial thigmotropic response and coiling take place in the tendrils, but subsequently, coiling also occurs in the inflorescence rachis which becomes sclerified and forms the permanent support structure for the vine. Thus, this species uses both stem and leaf homologues for support.

Key words: anatomy, Antigonon leptopus, development, Polygonaceae, tendril