About Sigmoidotropis speciosa (Kunth) A.Delgado
The scientific name of this species is Sigmoidotropis speciosa (Kunth) A.Delgado. The keel of Sigmoidotropis speciosa flowers is asymmetrical and strongly curved; this trait gives the species its common name, snail-vine. Multiple other species in the tribe Phaseoleae also have asymmetrical, curved keels, and some share the common name snail-vine. This has created significant confusion in the horticultural trade, where S. speciosa is very often misidentified as Cochliasanthus caracalla. In S. speciosa, flowers are solid pale purple, non-fragrant, and inflorescences bear only a small number of flowers. The keel curves in a single full circle, and the flower banner is largely symmetrical. By contrast, C. caracalla produces multicolored, fragrant flowers, has long inflorescences with many flowers, a keel curved in multiple circles, and a strongly asymmetrical banner. While some sources note differences in leaf color and size between the two species, it is not possible to reliably distinguish the two plants by foliage alone. There are many recorded cases where the two species were grown side-by-side for years, and their difference was only recognized when the less mature plant finally flowered. Like many other Phaseoleae with asymmetric flowers, S. speciosa is most likely pollinated by large bee species in its wild habitat. Some horticulturists report that flower-visiting ants can also pollinate cultivated S. speciosa. Flowers of Sigmoidotropis speciosa are solid pale purple. They grow alone or in small groups rather than in dense clusters, and each flower has five petals: one large wavy half-circle at the top called the banner, two tear-drop shaped inward-pointing petals called wings, and two keel petals that together form the thin, erect, curled keel. Depending on the viewing angle, the two wings can look like a single petal strongly resembling the banner. When this occurs, the three main visible petals form a shape like an open clam. The center of the flower and the tip of the keel may have a small patch of yellow and/or white, but this coloration is usually faint and only visible when examined closely. Immature flower buds typically form thick half-crescents; unlike corkscrew vine buds, these buds are green, yellow, or brown. Multiple growers note this plant grows very rapidly, and vines that touch the ground can take root. This growth habit makes Sigmoidotropis speciosa an invasive species, often compared to kudzu. It is also reported that the plant may be more susceptible to aphids. Sigmoidotropis speciosa can regrow even after all above-ground foliage is killed by frost.
