Molecular genetic evidence for interspecific hybridization among endemic Hispaniolan Bursera (Burseraceae)

Historically, genetic introgression among species as well as hybrid origins for species of the diploid tree genus Bursera (Burseraceae) have been proposed based on the supposition that individuals morphologically intermediate between sympatric "parent" species must be derived from hybridization. This study reports the first molecular genetic evidence for both unidirectional and reciprocal interspecific hybridization within Bursera. Phylogenies of hybrids and other species in B. subgenus Bursera are reconstructed based on nuclear and chloroplast sequence data. Compelling evidence supports the hybrid origin of three endemic Hispaniolan species: B. brunea (B. nashii * B. simaruba), B. gracilipes (B. spinescens * B. simaruba), and B. ovata (B. simaruba * B. spinescens). Cloning studies of nuclear markers from B. ovata suggests that this species is an introgressed or later backcross generation hybrid and thus reproduces sexually.