GASTONY, GERALD J.1* and GEORGE YATSKIEVYCH2. 1Department of Biology, Indiana University, Bloomington, IN 47405-3700; 2Missouri Botanical Garden, St. Louis, MO 63166-0299. - Morphological reassessment of molecular phylogenetic inferences in the xerically adapted cheilanthoid ferns (Pteridaceae: Cheilanthoideae).
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