Evolution of endosperm developmental patterns among basal flowering plants

A phylogenetically based comparative investigation of endosperm development was undertaken in a sample of 13 basal angiosperm taxa. The specific goals were to (1) provide a full developmental analysis of all aspects of endosperm in each species, (2) compare patterns among taxa to determine phylogenetic character distribution, (3) reconstruct the ancestral developmental pattern for angiosperms, and (4) explore scenarios of ontogenetic evolution that occurred during the early radiation of flowering plants. Five taxa, Acorus calamus, Cabomba caroliniana, Ceratophyllum demersum, Drimys winteri, and Platanus racemosa, are described in detail. Data from an additional eight taxa were analyzed and compared with these five. Endosperm ontogeny can be conceived of as a series of stages (characters) during which differential patterns of development occur among taxa (character states). We discovered that differential developmental fate of chalazal and micropylar domains is a common pattern among the endosperms of all basal angiosperm taxa and suggest that this may be a feature of endosperm development in all angiosperms. Differential development of chalazal and micropylar domains in endosperm in basal angiosperms also bears a marked similarity to what occurs in angiosperm embryos. This may have implications for understanding the evolutionary origin of endosperm. Basal angiosperms also exhibit variable endosperm developmental characters, indicating that significant ontogenetic transformation occurred during the early radiation of the clade, although magnoliid taxa exhibit a high degree of conservation in endosperm characters. Identification of the roles of the division of the primary endosperm nucleus and subsequent development of the chalazal and micropylar domains provides the first insight into how different endosperm developmental patterns are evolutionarily and developmentally related.