Evolution in the Acalypha gracilens/monococca complex (Euphorbiaceae): Morphological analysis

A variety of taxa at different ranks have been recognized within the Acalyp ha gracilens/monococca complex (Euphorbiaceae). In addition to emphasizing different characters in their treatments, taxonomists working on the group have interpreted the marked geographic variation in the group as evidence o f intermediacy among the taxa they recognize. Univariate and multivariate s tatistical analyses of morphological data drawn from herbarium specimens an d population samples demonstrate that many of the characters used to distin guish infraspecific taxa within A. gracilens vary clinally throughout much of the range of the species rather than demarcating recognizable units. Aca lypha monococca shows very little regional variation and is quite distinct from A. gracilens. Many features of A. gracilens parapatric to A. monococca are extreme relative to features of both A. monococca and A. gracilens all opatric to A. monococca. These results suggest that the variation in A. gra cilens is not due to hybridization with A. monococca, though the results al so demonstrate the limitations of morphological data in distinguishing hybr idization from primary divergence. Application of phylogenetic species conc epts supports specific rank for both taxa.