Eastern marsh fern

Description

Thelypteris palustris, the marsh fern, or eastern marsh fern, is a species of fern native to eastern North America and across Eurasia. It prefers to grow in marshy situations in full sun. The species epithet palustris is Latin for "of the marsh" and indicates its common habitat. It is the only known host plant for Fagitana littera, the marsh fern moth. 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. 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. An intermediate position is to place the bulk in Thelypteris (corresponding to Thelypterioideae of PPG I), 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 many genera, one of which is Thelypteris. This is the approach taken in the Pteridophyte Phylogeny Group classification of 2016 (PPG I).