Embryology and probable relationships of Eriospermum (Eriospermaceae)

Abstract

Three South African species of the African genus Eriospermum Jacq., which makes up Eriospermaceae Endl., have been studied in connection with the project “Families of Vascular Plants”, partly to establish the phylogenetic relationships of the family. The embryology is unusual in several features reflecting the advanced character of the genus in this respect. The following features are the most important: the tapetum is secretory; microsporogenesis is successive; the ovules are anatropous and crassinu‐cellate; the primary archesporial cell cuts off a parietal cell; the embryo sac formation is of the Polygonum type; endosperm formation is nuclear, but the endosperm is soon consumed, nucellus cells bordering on the sides of the chalazal half of the embryo sac divide to form a perispermal sheath around the embryo; embryo formation follows the Nicotiana variation of the Solanad type; the embryo of the mature seed is large and cylindrical‐obconical, reaches above the perisperm. The seed coat is formed by both the outer and the inner integuments, both 2‐layered; the epidermal cells of the test a grow out into long trichomes. The embryology and seed shape of Eriospermum is compared to those in Cyanastrum, Walleria, and genera of Tecophilaeaceae and some other families as far as details in these are known.