JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. The University of Chicago Press is collaborating with JSTOR to digitize, preserve and extend access to International Journal of Plant Sciences.The Galapagos endemic plants Scalesia aspera, Scalesia crockeri, and Scalesia pedunculata (Asteraceae) grow in distinct parts of Santa Cruz Island. Between them lie morphologically intermediate populations. The putative hybridization of the three species was investigated by means of morphological (leaf characters) and molecular (amplified fragment length polymorphism) measures. The results suggest that the intermediate populations are interspecific hybrids. Artificial hybrids were also made by crossing S. crockeri and S. pedunculata manually. We thus document that reproductive barriers are incomplete and that gene flow occurs between the three different species of Scalesia.