SCHUETTPELZ, ERIC1*, HARALD SCHNEIDER2, and KATHLEEN M. PRYER1. 1Department of Biology, Duke University, Durham, NC, 27708, USA; 2Albrecht-von-Haller Institut of Plant Sciences, University of Goettingen, 37073 Goettingen, Germany. - The phylogenetic history of Pterozonium (Pteridaceae) revisited: from groundplan divergence to maximum parsimony.
Pterozonium is a small genus of fourteen species of
homosporous, leptosporangiate ferns that are largely endemic to the
tabletop mountains of the Guayana Shield. These ferns have simple or
pinnate coriaceous fronds with elongate, exindusiate sori along their
free veins. In his 1967 revision of Pterozonium, D. B.
Lellinger studied the evolutionary history of the genus using the
groundplan divergence method. This method for constructing
phylogenetic trees was developed by W. H. Wagner in the 1950s as an
educational tool to illustrate systematic principles. Using
"primitive" or groundplan characteristics as a starting
point, this character-based method estimates the amount, direction,
and sequence of phylogenetic divergence among taxa. It essentially
employs a parsimony algorithm and is a precursor to modern-day Wagner
parsimony. From the 1950s to the 1980s, researchers doing monographic
studies frequently implemented groundplan divergence to estimate
phylogenetic relationships among taxa. This method has since been
replaced by a more stringent application of parsimony for the analysis
of morphological data. In an attempt to better understand the
interspecific relationships of Pterozonium and the relationship
between groundplan divergence and maximum parsimony methods, we
compare the results of Lellinger to our results of parsimony analyses
of Lellinger's data and of an expanded morphological data matrix. We
include several closely related genera not included by Lellinger, such
as Austrogramme, Eriosorus, and Taenitis,
allowing us to determine the phylogenetic root for Pterozonium
and the direction of morphological character state transformation in
the genus. This sets the stage for a concurrent study of the genus
that has been initiated using multiple molecular markers. We describe
similarities between the analyses using groundplan divergence and
maximum parsimony and discuss the potential of Pterozonium as a
model organism in which to study the relative roles of dispersal,
extinction, and vicariance in the biogeography of homosporous ferns.
Key words: biogeography, groundplan divergence, Guayana Shield, Pteridaceae, Pterozonium