Floral evidence for Cretaceous chloranthoid angiosperms

Abstract

The hypothesis that multiparted magnolialean flowers retain the largest number of primitive floral characters among living angiosperms has received support from almost 80 years of comparative studies with extant plants^1–3. Accumulating fossil data suggest, however, that large Magnolia-like flowers were probably preceded in the fossil record by smaller and simpler floral types, some of them perhaps related to the Chloranthaceae, a family generally regarded as being advanced within the Magnoliidae^2–4. The presence of chloranthoid plants early in the history of the angiosperms has been suggested by studies of dispersed pollen^4–7 and fossil leaves⁸, but the information on floral structure crucial to assessing the biology of these plants and their relationships within the Chloranthaceae, has so far been unavailable. We now provide new evidence of Cretaceous chloranthoid angiosperms based on fossil androecia, with pollen in situ, from the Lower Cretaceous of eastern North America and the Upper Cretaceous of southern Sweden. The Cretaceous material clarifies the homologies of chloranthoid androecial structures and provides an improved basis for interpreting the pollination biology in this enigmatic group of early angiosperms.