A Partial Taxonomic Revision of the Rhynchocarpa Clade of Commiphora (Burseraceae) Endemic to Madagascar

Abstract

Recent molecular phylogenetic studies of Commiphora (Burseraceae) have revealed a complex history of species evolution in this genus, which includes four separate invasions of Madagascar. Two of these invasions have resulted in radiations of species that are not wellcharacterized taxonomically due in part to a lack of sufficient herbarium collections. Recent work has also revealed that morphological characters that have been used historically to circumscribe species of this genus have proven insufficient for distinguishing the closely related Malagasy species of these radiations. In this study we present a partial taxonomic revision for the most species-rich of these clades, the ‘Rhynchocarpa’ clade, which contains at least 26 species united by numerous molecular synapomorphies yet lack a shared, derived suite of morphological traits. Here, we revise seven ‘Rhynchocarpa’ species that are united by the presence of stellate pubescence on vegetative and reproductive parts of the plant, a trait that is uncommon in the genus and a practical metric for limiting the scope of the revisionary work. We include five new species, including four new names (Commiphora andranovoryensis, Commiphora elliptica, Commiphora morondavensis, and Commiphora razakamalalae) and a name currently in use, correctly published (Commiphora falcata). We provide morphological descriptions, distributional information, and conservation assessments for these as well as Commiphora aprevalii and Commiphora stellulata. We designate a lectotype for Commiphora stellulata. A key to the seven species is included. We envision this contribution as the first in a series of clade-based revisions that clarify the taxonomy of Malagasy Commiphora.