Seed ontogeny in Adesmia securigerifolia (Fabaceae‐Adesmieae)

Abstract

A study of the reproductive processes of Adesmia securigerifolia from bud to mature seed was carried out by means of field observations and the paraffin technique. Observations revealed the following new contributions to the study of legume embryology: 1) after fertilization, a small nucellar haustorium, or micropylar nucellar beak, was observed for the first time, originating from two obliterating nucellar cells that extended outwards. Their globose distal end comes in contact with the internal carpel wall, while the wedge shaped base stretches into the micropyle; a suspensor consisting of five or more cells ‐ the two basal cells are large and falcate and fit into the micropylar pore ‐ coexists with the undivided polar nuclei thus showing that endosperm formation begins after zygote division; 2) at the young embryo stage, a sac‐ shaped nuclear haustorium, formed by the endosperm, adjoins the outer integument and is not connected to the chalaza, or any vascular element; at the hilar level, a nucellar projection is formed in connection with the haustorial coenocytic endosperm. This projection persists up to the mature seed stage when it starts to degenerate, after performing another linking with the embryo nutrition system; 3) at the mature seed stage, the seed coat evolving from the outer integument has a single macrosclereid layer, though inclusions in the cell vacuoles simulate the presence of more layers and/or transverse walls. The lens, a hypodermal layer of osteosclereids (hour‐glass cells), and the astrosclereids are also described.