An embryological study of Bauera capitata with comments on the systematic position of Bauera

Abstract

In Bauera capitata Ser. ex DC. the anthers are tetrasporangiate with a three- or four-layered anther wall. The tapetum is glandular and its cells remain uninucleate. Tannin accumulates in the epidermis and the endothecium, and many connective cells in addition contain druses. Simultaneous cytokinesis leads to tetrahedral and isobilateral tetrads of microspores. The pollen is shed when two-nucleate and is gorged with starch. Degeneration of contents of one or more sporangia is frequent.

The ovules are anatropous, crassinucellar and bitegmic. Twin microspore tetrads and twin embryo sacs are common but only one embryo sac reaches maturity. The development of the embryo sac follows the monosporic, Polygonum type. Starch accumulates in the mature embryo sac and remains until the initiation of endosperm. The antipodal cells persist until fertilization and rarely multiply.

The seeds are frequently sterile but contain a well-formed outer integument. The healthy seeds have in addition a five- or six-layered inner integument, a nuclear type of endosperm and an embryo.

The embryological evidence points to a closer affinity of Bauera Banks ex Andr. to the Cunoniaceae than to the Saxifragaceae.