Reinterpretation of the mid-Cretaceous fossil flower Endobeuthos paleosum as a capitular, unisexual inflorescence of Proteaceae

Abstract

The Myanmar amber fossil Endobeuthos paleosum was originally described as composed of an individual flower with a calyx of numerous, helically arranged sepals, a whorl of petals, and 60+ stamens each bearing a single bisporangiate anther. The 6 flowers, embedded together in a single block of amber, were described as varying in their calyx pubescence and length of corolla segments. The numerous stamens, with their single anther, led to a hypothesized relationship with certain members of family Dilleniaceae. We now propose a complete reinterpretation of this fossil as being an involucrate capitulum of family Proteaceae, in which the numerous “stamens” are identified instead as staminate flowers, although of reduced and highly modified morphology. Organs previously called the calyx and corolla are instead a series of helically-arranged bracts that surround the tight cluster of flowers. The Proteaceae being a diverse and significant element in Southern Hemisphere floras, the reinterpretation of Endobeuthos is important in providing the first Cretaceous fossil flower identified for the family, dated at some 20 my younger than the proposed Proteaceae crown group age of 119 Mya.