3. Dryopteris cristata (L.) A. Gray (crested shield fern) Pl. 7c,d; Map 23

Rhizome and petiole scales tan, concolorous, not shiny, linear to ovate. Leaves 35–80 cm long, slightly dimorphic, the plants sometimes producing overwintering rosettes of shorter, flat, leaves, herbaceous to papery. Leaf blades narrowly lanceolate to narrowly oblong in outline, tapering gradually to the base and broadest at or above the middle, pinnately compound, glabrous, the pinnae of fertile leaves often twisted like venetian blinds at right angles to the plane of the leaf. Pinnae 2–9 cm long, triangular to narrowly deltoid or linear, the tips mostly acute, the margins shallowly toothed, the pinnae usually deeply lobed. Basal lower segment of basal pinna about as long as the basal upper segment and slightly longer than the adjacent basal segment. Sori about halfway between the midribs and margins of the pinnules or pinnule lobes. Indusia glabrous, thin, usually shriveling at maturity. Spores 55–62 mm long. 2n=164. June–September.

Uncommon, known only from Clark County (northeastern U.S. south to North Carolina and disjunctly west to Nebraska, Canada). Wet hummocks in a mesic bottomland forest near a spring.

This tetraploid species arose following hybridization between the southeastern D. ludoviciana (Kunze) Small and another unknown, diploid, possibly extinct taxon known to hopeful botanists by the unpublished name, “D. semicristata.” D. cristata is unique among Missouri species of Dryopteris in its narrow leaf blades and the tendency for the pinnae to become oriented at right angles to the plane of the leaf, giving them a louvered appearance. Thus far it is known from a single site in the northeasternmost part of the state, where it occurs in a marshy forest adjacent to a large spring-fed wetland complex.