RAPD differentiation between Borderea pyrenaica and B. chouardii (Dioscoreaceae), two relict endangered taxa

As currently circumscribed, the genus Borderea Mieg. comprises two narrowly distributed European taxa, Borderea pyrenaica (Bub.) Mieg. and B. chouardii (Gaussen) Heslot. An accumulation of facts such as that both species share a very close overall morphology, that only a single population of Borderea chouardii is known, and that they live in contrasting environments has led some authors to suggest that B. chouardii is a mere ecotype of the more widespread B. pyrenaica. We tested this hypothesis using RAPD markers in four populations of Borderea, three of them identified as B. pyrenaica and the other one representing the only known population of B. chouardii. Eleven out of twenty assayed primers yielded consistent and reproducible polymorphims between accessions. Overall, 145 reproducible bands were scored, 116 of which (80.0%) were variable between samples. Mean similarity values within Borderea pyrenaica populations were lower (0.78) than those obtained for B. chouardii (0.94); pairwise similarities among B. pyrenaica populations were practically identical (0.73). A low similarity value (0.31) was obtained when comparing Borderea chouardii to each of the three populations of B. pyrenaica. The number of taxon-specific RAPD bands that distinguish both taxa was high (34); all of them were present in Borderea chouardii and absent in B. pyrenaica. Furthermore, another 13 polymorphic marker bands discriminated the two entities; 10 of them were only present in B. pyrenaica, whereas the other 3 were exclusively in B. chouardii. Multivariate analysis showed a strong taxonomic signal in the data set, irrespective of the number of RAPD markers used or the number of plants analyzed. These results strongly suggest that (i) Borderea chouardii is not an ecotype of B. pyrenaica and that both taxa should be granted the specific level, and (ii) B. chouardii is not a recent derivative of B. pyrenaica.