1. Cercis L. (redbud)
Four to 14
species, temperate regions of North America, Europe, Asia.
Molecular
studies have indicated that Cercis and the large tropical genus Bauhinia
(orchid trees) are closely related and together occupy a basal position within
the Fabaceae (Bruneau et al., 2001). The simple leaves of Cercis are
thought to be derived from a pair of leaflets or lobes like those found in most
Bauhinia species. Two species of Cercis have been described from
North America: the wide-ranging C. canadensis in the eastern United States and Mexico, with more pointed
heart-shaped leaves, and C. occidentalis Torr. & A. Gray in California, with more
rounded, kidney-shaped leaves. Bruneau et al. (2001) concluded that C.
canadensis is more closely related to the Eurasian C. siliquastrum
L. than to C. occidentalis. The relationship probably dates back to the
early Tertiary period when the two continents were much closer to another than
in modern times (Davies et al., 2002).