Genetic relationships and population structure within taxa of the endemic Sideritis pusilla (Lamiaceae) assessed using RAPDs

RAPD analysis has been performed for 15 plant populations, covering eight different infraspecific taxa of Sideritis pusilla (Lange) Pau, member of the Lamiaceae endemic to southeastern Spain, and their putative parental species Sideritis hirsuta L. and Sideritis leucantha Cav. Genetic distances, together with the presence of numerous fixed molecular markers differentiating S. pusilla from its putative ancestors, indicate that it should be considered as a true species. Cladistic and populational analysis led to the allocation of S. pusilla populations into three major groups-osteoxylla, flavovirens and pusilla/almeriensis-which include taxa previously described as ranging from the varietal to the specific level. Low genetic differ differentiation among groups revealed by a reduced number of specific molecular markers justify their assignment under the infraspecific range. Moreover, the existence of both morphological and biogeographical differences, supports a status for these groups as subspecies of S. pusilla. Highly significant (P<0.002) variance partitioning data (AMOVA) extracted fr om the analysis of individuals within S. pusilla populations show that, of the total genetic diversity, 68.8% was attributable to individual differences within populations, 19.9% to populational differences within groups, and only 11.3% to divergence between groups. This distribution is in agreement with the outcrossing nature of these plants. Comparative analysis of variance within populations reveals a reduced genetic variation for the osteoxylla group, thus supporting its previous consideration as an endangered taxon. (C) 1999 The Linnean Society of London.