The extent of clonality and genetic diversity in the Santa Cruz Island ironwood, Lyonothamnus floribundus

Lyonothamnus floribundus, or island ironwood, is a relictual endemic species found on only four of the eight California Channel Islands. It has been suggested that this species is capable of clonal growth, although the extent of clonality has not been determined. We have used random amplified polymorphic DNA (RAPD) analysis to examine clonality and genetic diversity in L. floribundus. We found that groves are largely genetically distinct clones, indicating that they are not remnants of a once larger clonal forest. Our data also indicate that the population size of L. floribundus on Santa Cruz Island is closer to 1125 individuals, rather than 32 000 based on the number of trunks. The extensive clonality in this species may have a severe impact on its ability to reproduce sexually owing to limitation of pollinator movements among flowers within a single individual. In addition, our data indicate that the two subspecies of L. floribundus are very closely related rather than being two distinct lineages dating to the Miocene, as indicated by the fossil record.