Microsporogenesis and microgametogenesis of the Argentinian species of Podocarpus (Podocarpaceae)

The development of the microsporangium and male gametophyte of three species of Podocarpus was studied with light microscopy (LM) and the morphology of pollen with scanning and transmission electron microscopy (SEM and TEM). During early stages, the male cone is covered with coriaceous scales. The archesporid cells go through a dormant period. Later the pollen mother cells differentiate and undergo meiosis. Callose is detected around the tetrad and between each monad. The microspore nucleus divides several times to give rise to a multicellular gametophyte, which includes the tube cell, the stalk and body cells, and four prothallial cells. The exine of the pollen grain is rugulate in the corpus and quite smooth in the sacci. The ultrastructure of the pollen wall consists of the alveolate sexine, the laminate nexine I and the amorphous nexine II. The intine is very thin. Comparison of the mature grain of some fossils with living members of the Podocarpaceae reveals great similarity.