Thelypteris (maiden ferns) is a genus of ferns in the subfamily Thelypteridoideae, family Thelypteridaceae, order Polypodiales. Two radically different circumscriptions of the genus are in use as of January 2020. In the Pteridophyte Phylogeny Group classification of 2016 (PPG I), the genus is a very small one with about two species. In other approaches, the genus is the only one in the subfamily Thelypteridoideae, and so includes between 875 and 1083 species.

The genus name is from Greek thēlys "female" and pteris "fern". However, "female fern" usually refers to the common lady-fern.

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