Isozyme evidence for natural hybridization in Phlomis (Lamiaceae): Hybrid origin of the rare P. x margaritae

Phlomis x margaritae is a rare and sterile hybrid taxon found in a single e ndangered population in southern Spain. It was previously described as a mo rphologically intermediate hybrid, putatively between Phlomis purpurea and P. composita. The present study used allozymes as molecular markers to asse ss the hybrid identity of P. x margaritae. Ten putative loci from seven enz yme systems were resolved: five were monomorphic and fixed across all taxa studied and the rest (Aat-1, Aat-2, 6-Pgdh-2, Pgi and Pgm) were polymorphic in at least one taxon. The two parental taxa are Fixed for different allel es at 6-Pgdh-2 and show distinct allelic frequency differences for four oth er loci. Phlomis x margaritae displays fixed heterozygous phenotypes for fo ur of the five polymorphic loci, these bring composed of combinations of th e alleles found in the parental tare. No unique alleles were detected in P. x margaritae. We conclude that this taxon is of hybrid origin and confirm the identity of the parental taxa involved. It is further suggested that th is population is composed of individuals that are recent F-1 hybrids that h ave nor undergone backcrossing or introgression. Global conservation measur es are necessary for the whole hybrid system in this location since further continuous assessment could reveal the evolutionary input of hybridization in Phlomis. (C) 2000 Annals of Botany Company.