Phylogeny of Rhododendron subgenus Hymenanthes based on chloroplast DNA markers: between-lineage hybridisation during adaptive radiation?

Rhododendron subgenus Hymenanthes comprises >200 highly interfertile species in SE Asia (mainly Himalayas and southern China) plus the 10–11 members of subsection Pontica (excluding R. hyperythrum) distributed outside SE Asia. Parsimony and Bayesian analyses of cpDNA matK and trnL-F sequence data divided Hymenanthes into two clades: clade H, in which two Pontica species and the SE Asian R. adenopodum were sister to a clade of 60 SE Asian species, and clade P comprising eight Pontica species plus R. praevernum, R. calophytum, and R. insigne from SE Asia. If these three species belong in Pontica, they expand its range substantially. However, as they have no morphological links to Pontica, they might descend from clade H species that captured chloroplasts from a now extinct species of Pontica. Either way, their distribution within the Chinese/Himalayan range of Rhododendron indicates an ancestor that came from the north or east to meet the diversifying group of Hymenanthes in the Himalayas, making the SE Asian members of Hymenanthes a polyphyletic group.