Meeting Abstract

P3.86  Sunday, Jan. 6  Taxonomic and adaptive significance of morphological variation in North American Cercis LEATHERMAN, L.S.T.*; NOWELL, C.; SCHILLER, A.M.; FRITSCH, P.W.; Oberlin College; San Francisco State Univ. and California Academy of Sciences; Evergreen State College; California Academy of Sciences

In North America, Cercis traditionally comprises the eastern species C. canadensis, composed of three vaguely-defined varieties, and the western species C. occidentalis. Although the two species are separated by nearly 1000 km, C. occidentalis is often difficult to distinguish morphologically from many populations of C. canadensis, and on this basis, alternative classifications recognizing from one to six species have been proposed for the group. This study employed morphometric methods to provide a comprehensive analysis of morphological variation in Cercis throughout North America. The data set is based on leaf and fruit characters of 882 herbarium specimens (including 281 used in a prior study limited to Texas and Mexico) sampled from throughout the range of North American Cercis. Analyses revealed continuous variation for most characters, with no two or more characters exhibiting overlapping gaps in variation, and with most characters more or less clinal. Thus, distinct taxa appear not to be warranted on morphological grounds. Leaf characters thought to be adaptive to mesic versus xeric climates were strongly and significantly associated with mean annual precipitation and temperature gradients—larger leaves with a more acute apex and shallower sinus occur in cooler, wetter areas of the eastern United States and southern Mexican cloud forests, whereas smaller leaves with a more rounded apex and deeper sinus occur in warmer, drier areas in the western United States, south-central United States, and northern Mexico. These correlations may prove useful in estimating climatic conditions for fossil flora where Cercis leaves occur.