Morphological variation in populations of Disa uniflora (Diseae: Orchidaceae) in the southwestern Cape, South Africa

Abstract

Measurements of sixteen floral and vegetative morphological features of individuals from seven groups of populations of Disa uniflora Berg. (Orchidoideae: Orchidaceae) in the mountains of the southwestern Cape Province of South Africa were used to analyze patterns of intraspecific variation. Each population group had between one and three populations, and each population had between 2 and 30 (mean, 21) individuals. The data were analyzed using multivariate statistical clustering methods. The covariance biplot analysis indicated the patterns of variation, while the phenetic methods were used to test correlations between the patterns of variation and geographical isolation and altitudinal variation. The results are interpreted in the light of competing hypotheses on ecological versus gene-flow models driving interpopulational divergence. Variation was found to be largely between mountain blocks, whereas both geographical distance and altitudinal differences were found to be significantly correlated with the variation patterns. Conservation implications for D. uniflora as well as other Cape species are discussed. Key words: geographic variation analysis, Orchidaceae, intrapopulation variation.