Embryology of Illigera and Sparattanthelium (Hernandiaceae, Laurales): Family Characteristics and Relationships

Abstract

The Hernandiaceae, a small family comprising five genera that are closely related to the Lauraceae and Monimiaceae, exhibit highly diverse morphological characters. Here, we present the first embryological study of Illigera and Sparattanthelium and, by comparing those data to those from Gyrocarpus and Hernandia, discuss the relationships in the Hernandiaceae and related families. Our embryological data indicate that the Hernandiaceae, which are characterized by a multiplicative outer integument, share several features (apomorphies) with the Lauraceae, including an amoeboid tapetum, a lack of hypostase, and exalbuminous seeds, suggesting a close relationship between them. Within the Hernandiaceae, Hernandia/Illigera (Hernandioideae) exhibit radially elongated tapetal cells in the anthers, monolayered pollen mother cells, anthers dehisced by laterally hinged valves, thick parietal tissue in the nucellus, a nucellar beak, a vascularized outer integument or testa, and a thick, persistent mesotesta. In comparison, Gyrocarpus/Sparattanthelium (Gyrocarpoideae) are characterized by an embryo sac protruding from the nucellus and a nonspecialized chalaza. Such marked diversity of embryological characters in the Hernandiaceae, as well as the great embryological gap between its two subfamilies, corroborates previous evidence of a deep split and early divergence of the family.