Species separation of Taxus baccata, T. canadensis, and T. cuspidata (Taxaceae) and origins of their reputed hybrids inferred from RAPD and cpDNA data

Abstract

Species delimitation in Taxus (Taxaceae) has been controversial due to high levels of phenotypic plasticity. Reputed hybrids between species have been questioned due to the original crosses' accidental nature and the uncertainty regarding the parent species' distinctness. In this study 19 samples from three species (T. baccata, T. canadensis, T. cuspidata) and 31 from putative hybrids (T. X hunnewelliana, T. X media) have been DNA-fingerprinted using RAPDs and characterized for their respective chloroplast genotype using restriction digestions of polymerase chain reaction- (PCR) amplified trnL-F fragments. All samples showed unique RAPD banding profiles. Twenty-one RAPD bands were species-specific; the presence of these bands in the putative hybrids confirmed the hybrid origin and parentage suspected from morphological studies (T. cuspidata X T. canadensis = T. X hunnewelliana, T. baccata X T. cuspidata = T. X media). Principal coordinates analysis (PCO) and unweighted pair-group method algorithm (UPGMA) analyses of RAPD bands clearly separated the species, indicating that they belong to discrete genetic stocks and supporting their individual species status. The two hybrid groups also clustered discretely. Chloroplast typing confirmed the direction of crosses. The data further suggested that repeated reciprocal crossings occurred in the production of the hybrid cultivars.