Who threatens who? Natural hybridization between Lotus dorycnium and the island endemic Lotus fulgurans (Fabaceae)

In contrast to its creative role in plant evolution, hybridization may be a cause for concern in efforts to preserve rare and endangered species. Threats can be more acute when population sizes are unequal and when barriers to introgression are weak. Lotus fulgurans is an endangered Balearic Islands endemic shrub related to the widespread Mediterranean species Lotus dorycnium. Both species are morphologically distinct when they grow together. However, morphologically intermediate individuals have been observed on the island of Minorca, in a single, narrowly localized, and apparently stable hybrid zone. Morphological and molecular markers suggest that gene flow between these two Lotus species is recurrent and polytopic. Contrary to expectations, the genetic integrity of the endangered L. fulgurans does not appear to be greatly compromised as interspecific gene flow is apparently unidirectional and biased towards L. dorycnium, and is restricted to three populations and a small number of individuals. (C) 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101, 1-12.