A genus of about 6 species, woody vines, shrubs, and small trees, of temperate e. Asia and e. North America. Some research suggests that the Asian species should be placed in a separate genus (see Isely 1998 and Stritch 1984).
ID notes:Twining direction can be determined by looking at (or imagining) the vine twining around a branch or pole. Look at the pole or branch from the base (from the direction from which the vine is growing). If the vine is circling the branch or pole in a clockwise direction, that is dextrorse; if counterclockwise, that is sinistrorse. Identification of the two alien species and their hybrids is uncertain. Genetic sorting of morphological characters and horticultural selection mean that morphology is only poorly correlated with genetic origin. Trusty et al. (2007) found that 24 of 25 individuals tested from scattered sites around the Southeast showed genetic admixture (sometimes complicated) between W. floribunda and W. sinensis. Probably the great majority of material in the Southeast could be called W. ×formosa; the below key may work poorly or not at all for some material encountered.