Morphological variation among populations ofLecocarpus(Asteraceae) on the Galápagos Islands

Abstract

Representative samples were collected from almost all known populations of the endemic Galapagos genus Lecocarpus. Multivariate statistical methods were applied to morphological characters to investigate differentiation among species and populations. In discriminant analysis no misclassifications were made among species. Populations of L. darwinii and L. lecocarpoides were better discriminated than populations of L. pinnatifidus. Principal Component Analysis (PCA) separated species well although intermediate populations occur between L. darwinii and L. lecocarpoides. Clear patterns of within-species differentiation were seen among populations of L. darwinii and L. lecocarpoides, but not among populations of L. pinnatifidus. Populations of L. lecocarpoides at present grow on separate islands. All populations of L. darwinii are found on San Cristobal, but this island might have been separated into more islands in the past. Lecocarpus pinnatifidus has probably always been growing on only one island. This suggests that the sea is the major barrier to dispersal of the three species. We find it likely that the degree of reproductive isolation caused by the sea is crucial to the differentiation among populations, and that genetic drift rather than adaptation has been responsible. The analyses cast new light on the identity of classic collections made by Darwin in 1835 and Stewart in 1906. © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007, 154, 523–544.