Rediscovery of the Galapagos endemic Lecocarpus leptolobus (Asteraceae), its morphology, distribution and taxonomy relative to its congeners

Abstract

Abstract We report the rediscovery of Lecocarpus leptolobus at its type locality, and restrict the latter to El Ripioso, San Cristóbal, Galapagos. We compare the morphology of the population at this site with other populations of Lecocarpus on San Cristóbal and other Galapagos islands. We conclude that L. leptolobus is a valid taxon endemic to the south-western half of San Cristóbal and is not synonymous with L. lecocarpoides, whereas populations further north-east on the same island constitute a separate species validly named L. darwinii. These two taxa support the idea of a former biogeographic barrier between the two halves of San Cristóbal. Plants at two of the easternmost localities of the south-western species show some characters intermediate between the two species, possibly representing introgression following easing of the barrier. The three specimens of Lecocarpus collected on San Cristóbal by Charles Darwin, all mounted on a single herbarium sheet, comprise one branch of L. leptolobus and two of L. darwinii. We identify possible sites for Darwin’s collections based on information about his explorations. We find grounds for accepting the taxon Acanthospermum brachyceratum as a subspecies of L. lecocarpoides endemic to Gardner-by-Española, Osborn and Xarifa islets, the first of these being the type locality, demonstrating that even narrow sea barriers can contribute to plant radiation in oceanic archipelagos. On the basis of our findings, we provide a new key to the taxa of Lecocarpus.