3. Asplenium pinnatifidum Nutt. (lobed spleenwort) Pl.
1i,j; Map 3
Leaves 3–22 cm long, monomorphic. Petioles brown at the base, green above, not
shiny. Leaf blades simple, deeply lobed and sometimes nearly compound at the
base, narrowly deltoid in outline, the tip long-attenuate, rarely rooting and
forming plantlets vegetatively. Veins free, rarely anastomosing. Spores 64 per
sporangium. 2n=144. May–October.
Uncommon in the eastern half of the Ozark Division (eastern U.S. west to
Oklahoma). Ledges and crevices of shaded sandstone and granite bluffs and
The lobed spleenwort is a fertile, tetraploid derivative that resulted from
hybridization between A. montanum and A. rhizophyllum. It
occupies habitats similar to those of A. bradleyi, and the sterile,
tetraploid hybrid between the two taxa is known as Asplenium ¥gravesii Maxon, or Graves's
spleenwort (Pl. 1c,d). This rare hybrid is vouchered by a single, historical
collection from Madison County.
Elsewhere, A. pinnatifidum has been documented to hybridize with A.
montanum (A. ¥trudellii Wherry), A. platyneuron (A. ¥kentuckiense T.N. McCoy), and A.
trichomanes (A. ¥herb-wagneri W.C. Taylor & Mohlenbr). The last two are
likely to be found in Missouri eventually. For a discussion of the
morphologically similar A. ¥ebenoides (A. platyneuron ¥ A. rhizophyllum),
see the treatment of A. rhizophyllum.