1. Dryopteris carthusiana (Vill.) H.P. Fuchs (spinulose wood fern) Pl. 6c; Map 21

D. austriaca (Jacq.) Woyn. ex Schinz & Thell. var. spinulosa (O.F. Müll.) Fiori

D. spinulosa (O.F. Müll.) Watt

Rhizome and petiole scales tan, concolorous, not shiny, linear to ovate. Leaves 25–95 cm long, monomorphic, herbaceous to papery. Leaf blades deltoid to narrowly elliptic in outline, 2 times pinnately compound above to often 3 times pinnately compound below, glabrous, flat. Pinnae 7–115 mm long, narrowly triangular to linear, the tips attenuate, the margins toothed, the pinnules mostly deeply lobed. Basal lower segment of basal pinnae 2 or 3 times longer than the basal upper segment and longer than the adjacent basal segment. Sori about halfway between the midribs and margins of the pinnules or pinnule lobes. Indusia glabrous, shriveling at maturity. Spores 49–62 mm long. 2n=164. June–October.

Uncommon and widely scattered in eastern and central Missouri (northern U.S. south to Washington and South Carolina, Canada, Europe, Asia). Moist slopes in mesic forests, often on acidic substrates, swamps, less commonly in bottoms of sinkholes and on ledges of shaded sandstone bluffs.

This tetraploid species arose following hybridization between D. intermedia and another unknown, diploid, possibly extinct taxon known to hopeful botanists by the unpublished name, “D. semicristata.” D. carthusiana greatly resembles D. intermedia, but can be separated from that species by the absence of tiny glands on the leaf blades and by the shape of the basal pinnae (see the key above).

The distribution of the spinulose shield fern is highly disjunct in the state with isolated occurrences in the Bootheel counties, the Ozark Border counties near St. Louis, the Glaciated Plains in northeastern Missouri, and a single occurrence in the bottom of a large sinkhole in Camden County in the Ozarks. Unlike D. intermedia, which grows predominantly on sandstone ledges, most of the populations of D. carthusiana in Missouri are on the forest floor.