6. Asplenium rhizophyllum L. (walking fern) Pl.
2e,f; Map 5
Camptosorus rhizophyllus (L.) Link
C. rhizophyllus f. auriculatum Hoffm.
Leaves 5–40 cm long, monomorphic. Petioles brown at the base, green above, not
shiny. Leaf blades simple, rarely forking at the tip, narrowly deltoid in
outline, the tip long-attenuate, often rooting and forming plantlets
vegetatively, the base with a pair of auricles, these rounded to
long-attenuate. Veins anastomosing. Spores 64 per sporangium. 2n=72.
Common nearly throughout Missouri, although less common north of the Missouri
River (eastern U.S. and adjacent Canada west to Kansas). Ledges and crevices of
shaded dolomite and limestone bluffs and boulders; rarely found on
This distinctive species is treated in the segregate genus Camptosorus
by some authors based upon the netted venation and simple leaves. However, it
forms hybrids with several other species of Asplenium and the characters
that distinguish it are unremarkable in the context of overall morphological
variation within the genus. Thus most modern botanists treat the walking fern
as a species of Asplenium.
Where the walking fern grows on boulders of wooded slopes it frequently occurs
in close proximity to the ebony spleenwort, which is primarily a plant of the
forest floor. Scott's spleenwort, the sterile, diploid hybrid between A.
platyneuron and A. rhizophyllum (Asplenium ¥ebenoides R.R. Scott, Pl. 2c,d),
occurs on dolomite and limestone boulders sporadically throughout the Ozark and
Ozark Border regions. It is intermediate in morphology between the parental species,
with leaf blades that are pinnately compound in the lower half and with the
pinnae and lobes irregular in size. Some plants of this hybrid resemble those
of A. pinnatifidum. However, the petioles are dull and green except at
the base in A. pinnatifidum, whereas they are shiny and reddish brown to
dark brown in A. ¥ebenoides.