KNOX, ERIC B.* AND JOSE L. PANERO. Department of Biological Sciences, Rutgers University, Newark, NJ 07102; Plant Resources Center, The University of Texas, Austin, TX 78713. - Evolution of the giant senecios revisited; comparison of ITS and cpDNA phylogenetic estimates.
The giant senecios (Dendrosenecio, Asteraceae) are a group of
'cabbage trees' endemic to the tall, equatorial mountains of eastern
Africa. The terminal taxa in this group occupy cells in a
conceptualized two-dimensional array in which the geographic locations
of the mountains comprise one dimension and the
altitudinally-stratified habitats on these mountains comprise the
second dimension. Chloroplast DNA (cpDNA) restriction-site variation
was previously used to construct a phylogenetic hypothesis for all
terminal taxa at all but one known site. Biogeographic interpretation
of this phylogenetic hypothesis suggests that (1) the giant senecios
originated at high altitude on Mt. Kilimanjaro, Tanzania, (2) most
movement between mountains occurred as high-altitude dispersal, and
(3) repeated colonization of lower-altitude habitats on the different
mountains resulted in most of the morphological convergence observed
within the group. New sequence data from the internal transcribed
spacer (ITS) region of the nuclear ribosomal repeat unit are used to
evaluate these phylogenetic and biogeographic hypotheses.
Key words: Asteraceae, biogeography, cpDNA, Dendrosenecio, ITS, phylogeny