Abstract: The formation of archegonium and oogenesis in the fern Phymatosorus hainanensis(Noot.) S. G. Lu were studied by light microscopy (LM) and transmission electron microscopy (TEM). Archegonia of P.hainanensis are produced among the branched trichomes under the apical notch of the female gametophyte. The section observations showed that archegonium originates from the initial cell of the gametophyte and it gives rise to a column of three cells by two unequal divisions. The upper cell develops into the neck of the archegonium, and the lower one develops into its basic jacket cells. The middle cell is the primary cell which contains relatively abundant organelles. It undergoes two unequal divisions, gives rise to the neck canal cell, then the ventral cell and the egg cell. The neck canal cell and ventral canal cell degenerate in the mature archegonium and a fertilization pore forms in the upper surface of the egg. This study elaborated in details the morphological characteristics of archegonium formation and oogenesis in P.hainanensis, and revealed developmental features of the female sexual organs in the fern.

Key words: Phymatosorus hainanensis, archegonium, neck canal cell, ventral canal cell, egg cell