Billburttia, a new genus of Apiaceae (tribe Apieae) endemic to Madagascar

The genus Billburttia is described to include two new species endemic to Madagascar, B. capensoides and B. vaginoides. Both species were tentatively placed within the problematic genus Peucedanum L. (as Peucedanum sp. A and Peucedanum sp. B) based on their dorsally compressed fruits lacking prominent dorsal ribs and with winged marginal ribs. Recently, however, the African members of Peucedanum have been shown to be only distantly related to the type of the genus and have therefore been segregated into six African endemic genera. While the Malagasy species appear superficially similar to members from one of these segregate genera, viz. Notobubon, they differ markedly in their fruit anatomical characters, notably a narrower commissure, six commissural vittae, vascular tissue in the tip of the ribs and sphaerocrystals distributed in and around the epidermis. The latter two characters apparently represent apomorphies for Billburttia. The non-peucedanoid affinity of the genus, as suggested by the fruit anatomical data, was confirmed using ITS and rps16 intron sequences. Both parsimony and Bayesian analyses of these data place Billburttia within the tribe Apieae of subfamily Apioideae and not closely related to either Peucedanum (Selineae) or the African peucedanoid genera (Lefebvrea clade of Tordylieae).