4. Asplenium platyneuron (L.) Britton, Sterns
& Poggenb. (ebony spleenwort)
A. platyneuron var. bacculum-rubrum (Featherm.) Fernald
A. platyneuron var. incisum (Howe ex Peck) B.L. Rob.
A. platyneuron f. serratum (E.S. Mill.) Ralph Hoffm.
Leaves 5–50 cm long, somewhat dimorphic, the vegetative leaves shorter,
prostrate to arching, with shorter pinnae. Petioles reddish brown to dark brown
their entire length, shiny, the color extending to nearly the tip of the
rachis. Leaf blades pinnately compound, linear to narrowly oblanceolate in
outline. Pinnae mostly alternate on the rachis, 4–35 mm long, the median pinnae
7–35 mm long, oblong to narrowly deltoid or nearly linear, the margins
shallowly to sometimes deeply toothed, mostly auriculate at the base of the
upper margin, the base truncate to broadly rounded, mostly overlapping the
rachis. Veins not anastomosing. Spores 64 per sporangium. 2n=72.
Common nearly throughout Missouri (eastern U.S. and adjacent Canada, locally
and disjunctly west to Arizona; Africa). Shaded banks and slopes in mesic to
upland forests, less commonly in crevices of boulders and bluffs, on both
calcareous and noncalcareous substrates.
The ebony spleenwort is a common member of the ground layer in Missouri
forests. Less commonly, it grows near the bases of boulders and bluffs, where
it sometimes occurs in proximity to plants of the walking fern (A.
rhizophyllum). For a discussion of A. ¥ebenoides, the sterile hybrid between these two
species, see the treatment of A. rhizophyllum.
Elsewhere, A. platyneuron has been documented to hybridize with A.
pinnatifidum (A. ¥kentuckiense T.N. McCoy), A. ruta-muraria (A. ¥morganii W.H. Wagner & F.S.
Wagner), and A. trichomanes (A. ¥virginicum Maxon). Backcrosses with A. ¥ebenoides (A. ¥boydstoniae (K.S. Walter) J.W.
Short) have also been documented. However, neither these backcrosses nor the
primary hybrids listed above have been documented from Missouri as yet. They
should be searched for in areas where other spleenwort species occur in
proximity to A. platyneuron.