Cystopteris tenuis (Michaux) Desvaux. Phen: May-Aug. Hab: Moist outcrops and cliffs of metamorphic and sedimentary rocks, occasionally in moist soils near rock outcrops or moist soil banks. Dist: NL (Newfoundland) west to MN and NE, south to VA, IL, MO, and AR (Peck 2011), and in the mountains to NC, TN, and n. GA.
Origin/Endemic status: Native
Other Comments: This species has been interpreted as a fertile allotetraploid derived from hybridization between C. protrusa and an extinct or currently undiscovered second parent (C. "hemifragilis"), with its genome symbolized HHPP (Paler & Barrington 1995).
Synonymy: = Ar, FNA2, Il, K1, K3, K4, Mo1, NE, NY, Pa, Tn, Va, W, Shmakov, Batkin, & Vaganov (2018); = Cystopteris fragilis (L.) Bernh. var. mackayi G.Lawson – C, F, G; = Cystopteris fragilis (L.) Bernh. var. mackayii G.Lawson – Tat, orthographic variant; = n/a – RAB; < Cystopteris fragilis (L.) Bernh. – WV; < Filix fragilis (L.) Underw. – S13