The more eastern Thelypteris simulata (Parathelypteris s.) is known as a disjunct in both southwestern Ontario and southern Wisconsin, and surely will eventually be found in Michigan, likely in the southwestern Lower Peninsula. It forms ± dense colonies in acid soils of forested swamps and bog margins, and may be distinguished from the common T. palustris by the lateral veins in the pinnae never forking and being finely gland dotted on the underside of the pinnae. A significant proportion of the lateral veins in the pinnae of T. palustris fork, and glands are absent.
1. Pinnae not strongly reduced in size towards the base of the frond, the lowest at least ½ the length of the middle pinnae.
1. Pinnae strongly reduced in size towards the base of the blade, the lowest scarcely 1 cm long and wide and much shorter than the middle pinnae.
All species found in Thelypteris
MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. January 21, 2018. http://michiganflora.net/genus.aspx?id=Thelypteris.