| Thelypteris palustris, Thelypteris noveboracensis|
Thelypteris (maiden ferns) is a genus of ferns in the family Thelypteridaceae, order Polypodiales. If the genus is defined fairly broadly, it contains 875 species, many of which are extremely similar to one another, and is found nearly worldwide. The ferns are terrestrial, with the exception of a few which are lithophytes (grow on rocks). The bulk of the species are tropical, although there are a number of temperate species.
The genus name is from Greek thēlys "female" and pteris "fern". However, "female fern" usually refers to the common lady-fern.
At one time, all thelypterioid ferns were included in the genus Dryopteris because of the sorus shape. However, there are a great many differences between the groups, and these plants are now segregated in their own family.
Some researchers include the entire family Thelypteridaceae in the genus Thelypteris; others divide the family into as many as 30 genera. An intermediate position is to place the bulk in Thelypteris (which can then be divided into subgenera and sections corresponding to the genera of other authors) but to separate out Phegopteris and Macrothelypteris. Another choice is to divide the family into a half a dozen or so genera, one of which is Thelypteris.
The genus includes the following species (incomplete list):Thelypteris aculeata, A.R.Sm., endemic to Ecuador
Thelypteris appressa, A.R.Sm., endemic to Ecuador
Thelypteris bonapartii, (Rosenst.) Alston, endemic to Ecuador
Thelypteris campii, A.R.Sm., endemic to Ecuador
Thelypteris chimboracensis, A.R.Sm., endemic to Ecuador
Thelypteris conformis, (Sodiro) A.R.Sm., endemic to Ecuador
Thelypteris correllii, A.R.Sm., endemic to Ecuador
Thelypteris dodsonii, A.R.Sm., endemic to Ecuador
Thelypteris elegantula, (Sodiro) Alston, endemic to Ecuador
Thelypteris euthythrix, A.R.Sm., endemic to Ecuador
Thelypteris fluminalis, A.R.Sm., endemic to Ecuador
Thelypteris inabonensis, Proctor, Puerto Rico
Thelypteris kunthii (Desv.) Morton (=T. normalis), southeastern United States
Thelypteris macra, A.R.Sm., endemic to Ecuador
Thelypteris nevadensis (Baker) Clute ex Morton, western North America
Thelypteris noveboracensis (L.) Nieuwl., New York fern, eastern North America
Thelypteris palustris Schott, eastern marsh fern, eastern North America
Thelypteris pilosa, (M. Martens & Galeotti) Crawford, Mexico, Central America, Alabama
Thelypteris puberula (Baker) Morton, Mexico, southwestern US
Thelypteris rosenstockii, (C.Chr.) R.M.Tryon, endemic to Ecuador
Thelypteris semilunata, (Sodiro) A.R.Sm., endemic to Ecuador
Thelypteris simulata, (Davenport) Nieuwl., Bog fern, Massachusetts fern, eastern North America
Thelypteris subtilis, A.R.Sm., endemic to Ecuador
Thelypteris verecunda, Proctor, Puerto Rico
Thelypteris yaucoensis, Proctor, Puerto Rico
The flavonoid Protoapigenone from Thelypteris torresiana (a native fern in Taiwan) is being studied in order to better understand the Epstein-Barr virus and may have potential in treating ovarian cancer.