| A combination of enzyme electrophoretic and morphological analyses were used to delimit the taxa in North American Cercis. The Eastern Redbud complex (ranging from Michigan, south into Mexico and from the east coast west to Kansas) is a highly variable group, both morphologically and enzymatically. Infraspecific recognition within the Eastern complex was not possible utilizing enzyme data, but morphologically, the complex was divisible into three subspecific entities, Cercis canadensis subsp. canadensis, C. c. subsp. texensis, and C. c. subsp. mexicana. Electrophoretic data indicate that gene flow among these three taxa is apparently not restricted. Morphological divergence is evident in the geographically disjunct populations in West Texas south into Mexico, where the two subspecies have apparently evolved separate adaptations to reduce water loss. This morphological distinction among the taxa is lost where they are growing in intermediate ecological zones and hybridization has occurred. The Western Redbud complex (from Arizona, Utah, Nevada, and California) was less morphologically variable but revealed three distinct entities at the enzyme level of analysis, Cercis californica subsp. californica, C. californica subsp. nephrophylla, and C. orbiculata. Vegetatively, the three taxa of the Western complex are inseparable, although Cercis californica subsp. nephrophylla shows trends toward a decrease in leaf surface area and shorter, broader pods. Based on floral characters, Cercis californica is separable from C. orbiculata, the latter having larger petals. Among these three taxa gene flow is apparently restricted, resulting in divergence at the isozyme level. The lack of morphological divergence may reflect the habitat similarity among the three taxa. Information gathered in this study support the recognition of six taxa in North American Cercis: Eastern complex--C. canadensis subsp. canadensis, C. c. subsp. texensis, C. c. subsp. mexicana; Western complex--C. californica subsp. californica, C. californica subsp. nephrophylla and C. orbiculata. |
