7. Asplenium ruta-muraria L. (wall-rue) Pl. 1a,b;
A. cryptolepis Fernald
A. ruta-muraria var. cryptolepis (Fernald) Wherry
Leaves 2–10 cm long, monomorphic. Petioles green except sometimes brown at the
very base, not shiny. Leaf blades 2–3 times pinnately compound, deltoid-ovate
to obovate or lanceolate in outline. Pinnae alternate on the rachis, 7–30 mm
long, triangular to obovate, the pinnules spatulate to nearly diamond-shaped
and usually toothed to shallowly lobed at the tip, rarely deeply lobed at the
base, the pinna bases not overlapping the rachis. Veins not anastomosing.
Spores 64 per sporangium. 2n=144. May–September.
Scattered in the Ozark and Ozark Border Divisions (eastern U.S. and adjacent
Canada; Europe, Asia). Pockets of dolomite and limestone bluffs, frequently in
fairly exposed conditions; also on shaded dolomite boulders along streams.
The relationship of North American plants to those in Europe, where both
diploid and tetraploid races of the species occur, are not well understood.
American plants have at various times been treated as a separate species, a
variety of the European species, or considered unworthy of taxonomic
recognition. As there are no clear morphological distinctions between European
and North American plants, they should continue to be treated as a single taxon
until more detailed studies are completed. In Europe, the tetraploid cytotype
of A. ruta-muraria is treated as ssp. ruta-muraria.
No hybrids involving wall-rue have been reported from Missouri. However,
elsewhere it has been documented to hybridize with A. platyneuron (A.
¥morganii W.H. Wagner & F.S.
Wagner), A. rhizophyllum (A. ¥inexpectatum E.L. Braun ex C.V. Morton), and A.
trichomanes (A. ¥clermontae Syme). Of these, the last is the least likely
to be found in Missouri, as wall-rue and maidenhair spleenwort do not grow in
close proximity in the state.