The phytogeography of leaf morphology in two species of North American Asters: Lasallea Novae-Angliae and L. Oblongifolia (Compositae)

Abstract

Width-to-length ratios of upper stem leaves ofLasallea novaeangliae andL. oblongifolia were determined from herbarium specimens and field collections. No distinct subgroups based on suchratios were found in either species. InL. novaeangliae the curve of the ratio versus number of individuals was skewed toward the narrow-leaf range. This phenomenon was present but less pronounced inL. oblongifolia. The histogram of leaf ratios forL. novaeangliae was somewhat weakly bimodal, suggesting a possible broad-leaf race, which has not been recognized nomenclaturally. The absence of bimodality in the histogram of leaf ratios forL. oblongifolia indicates the need to place Shinners’ narrow-leaved varietyangustatus in synonymy. Other traits such as height, degree of branching and the nature of the pubescence were also found to be of no significance. Slight geographic trends in leaf width occur in both species. No real evidence was found for nomenclaturally recognizing any eastern variant in either species. Thus, Shinners’ var.orientis is not recognized inL. oblongifolia either.