Population Structuring and Patterns of Morphological Variation in Californian Styrax (Styracaceae)

Recent studies of genetic variation within and among populations and phylogenetic estimates have provided evidence bearing on the evolutionary history and taxonomy of Styrax in California (S. redivivus). In this paper, data from these studies are further analyzed and integrated with new data from morphology to gain insight into the nature and taxonomic significance of character variation within this species. Six morphological characters thought to be important in the delimitation of infraspecific taxa within S. redivivus were measured on 52 herbarium specimens and analyzed with Pearson correlations and multivariate methods. Five characters are significantly associated with latitude and three characters are significantly multiply correlated with latitude. Permutation tests show a significant association between isozyme allelic variation and latitude. Principal components analysis of the morphological data does not reveal distinct clusters. The distribution of character variation shows that most characters vary along continuous latitudinal clines, and no character exhibits an evident gap in character states. Although principal coordinates and neighbor-joining analyses of the isozyme data, and discriminant function analysis of the morphological data suggest the presence of two groups within S. redivivus, the sum of evidence does not support the delimitation of infraspecific taxa. A taxonomic treatment of S. redivivus, a distribution map of historical Californian collections, and a key distinguishing S. redivivus from related taxa are presented. The species status of S. redivivus is justified, and implications of the data for conservation are discussed