Helianthus anomalus is a well characterized diploid hybrid species occurring in several geographically isolated sand dune habitats in Utah and Arizona. The parental species H. annuus and H. petiolaris can be found in the same area but show different habitat preferences. Helianthus annuus prefers heavy clay soils whereas H. petiolaris can be found on drier sandy soils. Endemic dune species often are characterized by avoidance of long-distance dispersal. Helianthus anomalus displays many characters that seem to follow this rule, e.g. large achene weight and non-shattering of fruits. We conducted a phylogeographic study to reconstruct the historical biogeography of this dune species and we also examined the possibility of recurrent hybrid origin using cpDNA-CAPS and nuclear SSR markers. At least seven populations of each species and 12 individuals per population were sampled and a haplotype tree was reconstructed. Our molecular data support poor long-distance dispersal capabilities and suggest several independent origins of the hybrid species H. anomalus on different dune systems.

Key words: Helianthus, hybridization, multiple origin, phylogeography