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 d ifferent infraspecific taxa of Sideritis pusilla (Lange) Pau, member of the Lamiaceae endemic to southeastern Spain, and their putative parental speci es Sideritis hirsuta L. and Sideritis leucantha Cav. Genetic distances, tog ether with the presence of numerous fixed molecular markers differentiating S. pusilla from its putative ancestors, indicate that it should be conside red as a true species. Cladistic and populational analysis led to the alloc ation of S. pusilla populations into three major groups-osteoxylla, flavovi rens and pusilla/almeriensis-which include taxa previously described as ran ging from the varietal to the specific level. Low genetic differ differenti ation among groups revealed by a reduced number of specific molecular marke rs justify their assignment under the infraspecific range. Moreover, the ex istence of both morphological and biogeographical differences, supports a s tatus for these groups as subspecies of S. pusilla. Highly significant (P<0 .002) variance partitioning data (AMOVA) extracted fr om the analysis of in dividuals within S. pusilla populations show that, of the total genetic div ersity, 68.8% was attributable to individual differences within populations , 19.9% to populational differences within groups, and only 11.3% to diverg ence between groups. This distribution is in agreement with the outcrossing nature of these plants. Comparative analysis of variance within population s reveals a reduced genetic variation for the osteoxylla group, thus suppor ting its previous consideration as an endangered taxon. (C) 1999 The Linnea n Society of London.