A new species of Xylopia (Annonaceae) from the Amazon Basin, with a review of trunciflorous cauliflory in the genus.

A new cauliflorous species of the pantropical genus Xylopia (Annonaceae) is described from the Amazon Basin. Xylopia rubrolineata sp. nov., is shown to be distinct from X. ochrantha, with which it had previously been confused. On the basis of its morphology, Xylopia rubrolineata is inferred to belong to a small subclade of X. sect. Xylopia. A review of cauliflory in the genus indicated that the evolution of trunciflorous cauliflory was limited in time and place, occurring in only nine of ca. 220 species, all in two subclades of X. sect. Xylopia and confined to the Amazon Basin and Brazilian Atlantic Forest. The distribution of the trait within these subclades suggests multiple gains or losses. Cauliflory in Xylopia is hypothesized to be a bet-hedging adaptation, which enhanced reproductive success during a period of rapid change in Late Miocene South America that created a mosaic of fluctuating environments and extinctions. An identification key to the nine known trunciflorous species is provided.