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.
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known to hopeful botanists by the unpublished name, “D. semicristata.”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.