The systematic position of Cubanthus and other shrubby endemic species of Euphorbia (Euphorbiaceae) in Cuba

Cubanthus (Euphorbiaceae) has traditionally been recognized as a small genus of three similar species restricted to Cuba and Hispaniola. In this study we used DNA sequence data from the nuclear ITS and chloroplast ndhF gene regions to investigate its systematic position and the position of four other shrubby Euphorbia species endemic to Cuba: E. cubensis, E. helenae, E. munizii, and E. podocarpifolia. The results demonstrate that all of these taxa belong to a well-supported Antillean clade nested within Euphorbia that also includes E. punicea and E. gymnonota. For that reason, we treat Cubanthus as a section of Euphorbia instead of a separate genus. Euphorbia sect. Adenorima is relegated to a synonym of sect. Cubanthus. New names are proposed for Cubanthus brittonii and Cubanthus linearifolius (Euphorbia millspaughii and E. scutiformis, respectively), and a new combination is made for Cubanthus umbelliformis (Euphorbia umbelliformis). Section Cubanthus belongs to clade C of Euphorbia and is part of a New World assemblage that includes members of sections Euphorbiastrum, Pteroneurae, Portulacastrum, Stachydium, and the former genus Pedilanthus. Based on both the molecular results and morphological differences, two subsections are proposed: subsect. Cubanthus and subsect. Moa. The molecular phylogeny supports the hypothesis that section Cubanthus radiated entirely within the Antilles and the nearby Bahamian archipelago.