Allozyme variation and taxonomical implications of the endemic rocky plant Erodium rupestre (Geraniaceae)

Erodium rupestre (Geraniaceae) is a taxon endemic to north-eastern Spain which has experienced significant changes in taxonomy and chorology. When first described, its distribution area was limited to Montserrat, a mountain near Barcelona, although later several populations from the pre-Pyrenean range were attributed to E. rupestre. However, some authors have assigned these as belonging to a distinct taxon. Starch gel electrophoresis has been used to resolve the taxonomic circumscription of the pre-Pyrenean populations and to evaluate the levels of genetic diversity and the population structure, taking into account all the populations studied (pre-Pyrenean and Montserrat mountain). Levels of genetic variation shown by E. rupestre s.l. are extremely scarce (P = 7.1%, A = 1.07, and H_e = 0.025), rather lower than those expected for endemic species. Moderate to high levels of inbreeding were detected, probably as a consequence of the population's genetic structuring (geitonogamy and biparental inbreeding). Genetic identity between the two presumable taxa is very high (I = 0.973), clearly suggesting that the two taxa form a single species. However, according to the allelic distributions among populations, the Montserrat population on the mountain itself may represent the first step of an allopatric speciation process.