PRYER, KATHLEEN M.İ*, HARALD SCHNEIDERİ, ALAN R. SMITHı, PAUL G. WOLF§, RAYMOND C. CRANFILLı, JEFFREY S. HUNTİ, AND SEDONIA D. SIPES§. İDepartment of Botany, The Field Museum, Chicago, IL 60605; ıUniversity Herbarium, University of California, Berkeley, CA 94720; §Dept. of Biology, Utah State University, Logan, UT 84322. - The closest living relative to seed plants: insights from four genes and morphology.
Extant vascular plants comprise free-sporing "pteridophytes"
(lycopods, Psilotaceae, Equisetum, and ferns) and seed plants
(gymnosperms and angiosperms). The evolution of vascular plants is
mostly a 470-million-year history of pteridophytes and gymnosperms,
which ultimately led to the domination of our terrestrial ecosystems
by angiosperms 100 million years ago. Pteridophytes traditionally are
depicted as having various paraphyletic relationships to seed plants
and are often thought of as "intermediate evolutionary
grades" of relatively minor significance in early land plant
evolution. Phylogenetic estimates based on single genes and/or
morphology yield weak evidence for the divergence and relationships
among these major groups of vascular plants. This is not entirely
surprising given that, with the exception of angiosperms, they all
evolved in the Paleozoic and had diverged by the late Devonian (ca.
400 mya). The long independent history of each of these lineages
ensures that resolving their relationships is not likely to be
revealed by a single data set. Data from four genes (rbcL,
atpB, rps4, nrSSU) and morphology was tested for
congruence and results from the combined analysis strongly corroborate
several weak inferences made from single data set trees. However, the
clear resolution provided by the combined analysis for a basal
dichotomy between seed plants and all other (non-lycophyte)
"pteridophyte" lineages is novel. This result differs
remarkably from most topologies found in the separate analyses for
each of the five data sets. Robust support for Psilotaceae +
Ophioglossaceae, as well as relationships among basal fern groups will
also be discussed.
Key words: congruence and combined analysis, genes, morphology, phylogeny, pteridophytes, seed plants