Abstract: According to Ching's system (1963) the Thelypteridaceae in Northeastern China includes two genera with each only one species i. e. Phegopteris polypodoides Fee and Thelypteris palustris (Salib.) Schott. In the present paper all stages of the development of gametophytes in the two ferns have been studied and compared.The main differences between them on the development of gametophytes are as folllows:Phegopteris polypodoides: ① The perine of the spore lophate and united in false reticulum. ② The germ filaments 2-7 cells long, each cell long cylindrical and linked each other in sausage-shap, the terminal cell of them curved, often with 3-7 branches. ③ Prothallial plate cells primarily ranged regularly, exhibited by transverse and longitudinal cell walls. ④ The hairs just occur when the anterior part of the prothallial plate 14 or occasionally 6 cells broad Stage. ⑤ The margin cells linked with the hairs protrude extremly and result in the margin lobulate. ⑥The prothallial development is more or less of the Adiantum-type (Nayar Kaur 1971) and the hairs occur late. ⑦ Vascular cells exceptionally observed on the midrib of the older female prothalli and they are united into a vascular system.Thelypteris Palustris:①The perine of the spore irregularly rugulate and with small spinate process. ② The germ filaments 2-6cells long withourt any branch, cells cylindrical ③ Prothallial plate cells throughout ranged irregularly.④ The hairs occur soon after the apical cell appeared on the germ filaments. ⑤The margin cells the hairs linked protrude slightly or not, without lobus on the margin of the prothalli. ⑥ The prothallial development is of the Aspidium-type (Nayar Kaur 1971). ⑦ Without vascular cells in the midrib of the prothalli.Before Ching's reclassification, the above two species all belonged to one genus i. e. Thelypteris. Ching (1963) classified them into two genera and each above species is the typus generis in each genus. According to our present work their development of gametophytes in the main characteristics differ obviously from each other, it is evident that China's idea is reasonable.Vascular cells in the median midrib of the older prothalli of Phegopteris polypodoieds were observed, is it either a reflex of their primitive characteristics or an abnormal structrue due to the induction of culture condition?

Key words: Fern gametophyte, Thelypteridaceae, NorthOeastern China