Recent molecular cladistic analyses based on rbcL and nuclear ribosomal DNA have provided new insights into putative evolutionary lineages within cheilanthoid ferns. The molecular approach was prompted in part by Tryon and Tryon’s inference that “convergence in adaptive morphology has undoubtedly been frequent among cheilanthoid ferns” and their conclusion that cheilanthoids are “the most contentious group of ferns with regard to a practical and natural generic classification.” Molecular studies may provide the framework for an evolutionarily natural generic classification, but nucleotide sequences do not provide practical data in taxonomic and floristic contexts. A set of morphological characters has therefore been proposed as the basis for new cladistic analyses of cheilanthoids, with taxa selected from among those used in the molecular studies that found two major clades in the subfamily. The large clade encompassing Pellaea sections Pellaea and Platyloma, Paraceterach, Astrolepis, Argyrochosma, and American Cheilanthes provides an ingroup for the morphological study, with outgroup taxa drawn from the sister clade containing Notholaena, other American and non-American Cheilanthes, and Pellaea sections Ormopteris and Holcochlaena, plus more basal Bommeria. These two major clades correlate well with base chromosome numbers of x = 29 or 27 in subclades of the ingroup, and x = 30 in the outgroup, including Bommeria, but x = 30 is retained as the plesiomorphic condition in some American Cheilanthes in the ingroup while x = 29 appears to be homoplastic in some species of the outgroup clade. Whether non-homoplastic morphological data are adequate to permit rigorous morphological cladistic analysis or permit only fitting these characters to the molecular tree remains to be determined.

Key words: Argyrochosma, Astrolepis, Cheilanthes, cheilanthoid ferns, Paraceterach, Pellaea