THE SISTER GROUP OF THE PALEOTROPICAL TRIBE ARGOSTEMMATEAE: A REDEFINED NEOTROPICAL TRIBE HAMELIEAE (RUBIACEAE, RUBIOIDEAE)

Abstract— The sister group of the monophyletic tribe Argostemmateae, including Argostemma and Neurocalyx , is not the tribe Hedyotideae, or a part of it, as earlier assumed, but the monophyletic tribe Hamelieae, here redefined. It comprises the genera Hamelia, Hoffmannia (here including Xerococcus), Deppea (here including Schenckia), Pinarophyllon , and Omiltemia . The two tribes Argostemmateae and Hamelieae are a monophyletic group characterized by seven synapomorphies. A cladogram is presented showing the relationships of the seven genera based on 31 characters. One group of characters, the aestivation of the corolla, is shown to be much more complicated than hitherto assumed. In the Hamelieae the aestivation can be imbricate (to the right or to the left and quincuncial or not), contorted (to the right), alternative, or even valvate. The Argostemmateae occur in the Old World Tropics, and their distribution supports the hypothesis that at least parts of southeast Asia are a part of Gondwanaland. The vicariant pattern within the Argostemmateae indicates that the large area from west Africa through northern India to southeast Asia is vicariant to Ceylon and southern India. The distribution of the Old World tribe Argostemmateae is vicariant to the essentially Central American tribe Hamelieae.