Key points are not available for this paper at this time.
David S. Barrington, Christopher H. Haufler, Charles R. Werth, Hybridization, Reticulation, and Species Concepts in the Ferns, American Fern Journal, Vol. 79, No. 2, Species Concepts in Pteridophytes (Apr. - Jun., 1989), pp. 55-64
Barrington et al. (Sat,) studied this question.