The taxonomic status of Helianthemum dumosum, the rare and endangered Bushy Rockrose, was investigated using morphological and molecular methods. Helianthemum dumosum has a highly restricted range, found mainly on coastal heathland habitat in southern New England (especially Cape Cod, Nantucket, and Martha’s Vineyard) and Long Island, NY. However, it is often confused with the geographically widespread and sympatric close relative, H. canadense, and morphological intermediates between the two have been found. We searched for taxon-specific molecular markers and evidence of hybridization and introgression between the two using the high-resolution fingerprinting technique of intersimple sequence repeats (ISSRs). We performed multivariate statistical analyses and a comparative cladistic analysis between the ISSR data and morphological data. Preliminary results indicate that a pattern of clinal variation between the two taxa exists.

Key words: Cistaceae, coastal heathland, Helianthemum, ISSR, rare plant