In 1818, Thomas Nuttall observed that it was always distinguishable from "A. rhizophyllum", and described it as a species under the name of "Asplenium pinnatifidum". Alphonso Wood used the name "Camptosorus pinnatifidus" for the species in 1870, but this was not widely accepted. Oliver A. Farwell, observing an unusual specimen of "A. pinnatifidum", was led to suggest that the species might be a hybrid between American walking fern, "Camptosorus rhizophyllus" (now "A. rhizophyllum"), and ebony spleenwort ("A. platyneuron"). Such a hybrid, Scott's spleenwort ("A. × ebenoides") was already known, but Farwell thought it bore a greater affinity to "A. platyneuron" while "A. pinnatifidum" had a greater affinity to "A. rhizophyllum." He was correct in viewing "A. pinnatifidum" as a hybrid descendant of "A. rhizophyllum", but incorrect in identifying the other parent, and his suggestion was not widely taken up in the literature. Nor did his later attempt at subdividing "Asplenium", moving "A. pinnatifidum" to a new genus as "Chamaefilix pinnatifida" in 1931, meet with much favor. As a member of the "Appalachian "Asplenium" complex", "A. pinnatifidum" readily acts as the progenitor of hybrids, as well. "A. × gravesii" was recognized as a hybrid of "A. pinnatifidum" and "A. bradleyi" by W. R. Maxon in 1918. Edgar T. Wherry noted the similarities between "A. montanum", "A. pinnatifidum", and "A. × trudellii" in 1925, and in 1936 concluded that Trudell's spleenwort was a hybrid between the first two. That same year, "A. kentuckiense" was described by Thomas McCoy; Wherry identified it as a hybrid between "A. pinnatifidum" and "A. platyneuron".