Thelypteris, commonly known as maiden ferns, is a genus of ferns in the family Thelypteridaceae (order Polypodiales). The genus is notable for its deeply contested circumscription: under the Pteridophyte Phylogeny Group classification of 2016 (PPG I), it is a small genus of only about three accepted species; under broader treatments favoured by many pteridologists, the entire subfamily Thelypteridoideae — comprising between 875 and 1,083 species — is placed within a single, expansive Thelypteris. Intermediate approaches retain Thelypteris as the principal genus of the subfamily while recognising segregate genera such as Phegopteris, Macrothelypteris, Amauropelta, Christella, and Parathelypteris.
Historically, all thelypterioid ferns were treated within Dryopteris on the basis of a similar sorus shape, but the two groups differ substantially in other characters and are now universally placed in their own family. The three species accepted under the PPG I circumscription are Thelypteris confluens, Thelypteris krayanensis, and Thelypteris palustris; the last is the marsh fern, a widespread wetland species found across the Northern Hemisphere.
Etymology
The name Thelypteris derives from the Greek words thēlys ("female") and pteris ("fern"). Despite this etymology, the common name "female fern" is traditionally applied not to this genus but to the lady-fern (Athyrium filix-femina).
Distribution
Thelypteris in the broad sense is cosmopolitan, with species occurring on every continent except Antarctica. In the narrow PPG I sense, the three accepted species have disjunct distributions: Thelypteris palustris is a widespread Northern Hemisphere wetland fern (Europe, Asia, North America), Thelypteris confluens occurs in Africa and Asia, and Thelypteris krayanensis is known from Southeast Asia.
Taxonomy Notes
The circumscription of Thelypteris is one of the most contested in pteridology. All thelypterioid ferns were once placed in Dryopteris based on sorus morphology, but subsequent study revealed numerous distinguishing characters warranting a separate family, Thelypteridaceae. Three broad approaches exist: (1) the narrow PPG I (2016) view, which accepts only ~3 species; (2) an intermediate view retaining a large Thelypteris alongside segregate genera such as Phegopteris and Macrothelypteris; and (3) the broadest view, which sinks the entire subfamily Thelypteridoideae (875–1,083 species) into a single Thelypteris.
