Abstract:Microsporogenesis and male gametophyte development of Uncaria hirsuta Havil. (Rubiaceae) were studied under light microscopy (LM) and transmissiom electron microscopy (TEM). Flowers of U. hirsuta are monoclinous, which each have five stamens, and the anther is tetralocular. The anther wall is composed of epidermis, endothecium, middle layer(s) and tapetum, the endothecium becomes fibrously thickened at anther dehiscence. The development of the anther wall is the dicotyledonous type, the cytokinesis following meiosis is simultaneous, producing tetrahedral tatrads and rarely isobilateral ones. The exine deposition is initiated during the tetrad stage, and the intine formation begins at vacuolated microspore stage. Mature pollen grains are two-cell type. The ontogenetic features of microsporogenesis and male gametophyte development in U. hirsuta basically follow the pattern of Rubiaceae. The tapetum is secretory type, and dual ontogeny, originating from the parietal layers and connective-derived layer, respectively. Tapetum begins to degenerate at the early stage of free microspore, producing lots of ubisch bodies, and it becomes completely degenerated at anther dehiscence. Protruding onci occur at uninucleate microspore stage, most of which shed during binucleate microspore stage. It is preliminarily presumed that the protruding onci might play an important role in pollen development.
