Dryopteris carthusiana (Vill.) H.P. Fuchs
Dryopteris austriaca (Jacq.) Woynar ex Schinz & Thell. var. spinulosa (O.F. Müll.) Fisch.
Dryopteris spinulosa (O.F. Müll.) Watt
Spinulose wood fern, spreading wood fern, toothed wood fern, narrow buckler fern
Spinulose wood fern is named because its leaves have tiny spinules (spines) on their tips. The genus Dryopteris translates to ”fern of the oak wood,” and the species carthusiana honors Johann Friedrich Cartheuser, a polymath who died in 1777. Cartheuser was a physician, naturalist, anatomist, botanist, pathologist, chemist, pharmacist, and prolific author.
Identification: These ferns grow in uneven clumps or solitary fronds, and are 12-36" (30-91 cm) high. They prefer moist habitats. Fronds are 6-30" (15-76 cm) long and 4-12" (10-30 cm) wide. Each frond consists of primary leaflets (pinnae), composed of secondary leaflets (pinnules), which in turn are sometimes composed of tertiary leaflets, for which I couldn’t find a fancy name. This triple hierarchy makes these ferns (along with many others) tripinnate. And just to make sure you’re still paying attention, the tertiary leaflets are replete with little serrations called spinules, making spinulose wood ferns practically quadropinnate, a word that I’m pretty sure doesn’t exist. Leaflet bottoms contain the ferns’ reproductive structures, or sori, which are small, brown rounded mounds. At close range, the sori look like microminiature shrubs, about ¹/₁₆" (2 mm) in diameter.
Dryopteris carthusiana on Earl J.S. Rook's Flora, Fauna, Earth, and Sky ... The Natural History of the Northwoods
Dryopteris carthusiana on the Connecticut Botanical Society's Connecticut wildflowers site
Dryopteris carthusiana at Ontario Ferns
Cobb, Boughton, Farnsworth, Elizabeth & Lowe, Cheryl, Peterson Field Guides: A Field Guide to Ferns and Their Related Families of Northwestern and Central North America, Houghton Mifflin Company, 2005, p. 132
Dryopteris carthusiana description by Thomas H. Kent, last updated 25 May 2020.