Reassessing Inflorescence and Floral Morphology and Development inHedyosmum(Chloranthaceae)

Abstract

Hedyosmum (Chloranthaceae), one of the oldest angiosperm lineages, possesses some atypical reproductive features that remain poorly understood, including the inflorescence architecture, the stamen anatomy, and the perianth development around the allegedly inferior ovary. Our developmental survey of these characters with LM and SEM techniques showed that both staminate and carpellate partial inflorescences are indeterminate and suggests that each stamen corresponds to a single, ebracteolate flower. The tapetum is secretory and associated with orbicules; the connective apex is secretory, which—along with the reticulate pollen and the frequent visits of insects—suggests that entomophily should not be ruled out in Hedyosmum. The perianth is formed by three almost completely fused hypogynous tepals; the window is schyzogenous, unique among angiosperms, and according to the fossil record, it has been in the genus since the Early Cretaceous. Unlike any previous description, we found that the ovary is fully superior. The persistent perianth completely surrounds the fruit; in turn, they are tightly enclosed by the fused, acrescent, fleshy flower-subtending bracts, which appear to play a threefold role in protection, secretion, and dispersal.