The development of gametophytes and oogenesis in the fern Pronephrium penangianum

The development of gametophytes and oogenesis in the fern Pronephrium penangianum were investigated using microscopy technology. The results showed that the spores of P. penangianum were brown and dihedral and its spores germinated about 12 d after sowed. Then, they were developed into cordate prothallus through filament and plate stages. The spore germination was of Vittaria-type. The development of prothallus was of Drynaria-type. The mature prothallus was heart-shaped. After 46 d of spore sowing, the archegonium and antheridium were formed. The archegonium of P. penangianum originated from the initial cell beneath the growth point. The initial cell was divided into three cells by twice cell divisions, which were top cell, primary cell and basal cell. Among them, the primary cell was divided into a central cell and a neck canal cell after a division. Subsequently, the central cell underwent a division to form a ventral canal cell and an egg cell. With the development of egg, the neck canal cell and ventral canal cell gradually degenerated. Finally, only a pore region connected the egg and the ventral canal cell. When the egg cell matured, the upper surface of the cell had obvious egg envelope, and there was a fertilization pore in the center. This study is of great significance for enriching the reproductive biology of pteridophytes and exploring the evolution of ferns.