Infraspecific diversity of Cytisus emeriflorus Reichenb. (Leguminosae), anendemic plant with disjunct distribution: evidence from isozyme data

C. emeriflorus is an endemic species occurring in two disjunct areas some 2 00 km apart: the Pre-Alps of Lombardia and the Pre-Alps of Friuli. Four pop ulations from the western area and five populations from the eastern area w ere sampled in order to ascertain the amount and the distribution of variat ion throughout thr range of the species. Phenetic measures of isozyme polym orphism were used. Diversity values shoe ed that the species is polymorphic , despite its restricted distribution and the small population size; phenet ic distances revealed that partitioning of diversity was largely within rat her than among populations. Moreover, little differentiation was round betw een the two disjunct areas, although the western populations exhibited a sl ightly higher diversity compared with the eastern ones. The high level of p olymorphism and the overall similarity between populations from the two are as may be ascribed to past contacts, and indicate chat, despite the present widespread disjunction, the two areas have not evolved independently long enough for divergence to have occurred. There is no evidence that C. emerif lorus is at present genetically depauperated, although its range of distrib ution must have been much broader in the past; its present reduced distribu tion area and the small population size may be mainly due to ecological fac tors.