TAYLOR, DAVID WINSHIP1*, GILBERT J. BRENNER2, SA'D H. S. BASHA3, and ALI H. AL-HAMMAD3. 1Department of Biology, Indiana University Southeast, New Albany, IN, 47150 USA; 2Department of Geological Sciences, State University of New York, College at New Paltz, New Paltz, NY, 12562 USA; 3Department of Geology, P.O. Box 17114, University of Jordan, Amman, Jordan. - Lower Cretaceous evidence for the Cabombaceae water lily lineage and implications for molecular divergence in ancient monophyletic clades.
Most molecular phylogenies suggest that there are two well supported
clades in the Nymphaeales: the Cabombaceae clade and the Nymphaeaceae
- Barclayaceae clade. Recently flowers of the Nymphaeaceae -
Barclayaceae clade have been described from the Lower Cretaceous of
South America and Europe, whereas we describe vegetative evidence of
the Cabombaceae clade. The Brasenia-like fossils have leaves
with long petioles which are attached to slender shoots in an
alternate arrangement. The leaves are orbicular, simple with entire
margins, and peltate with the petiole attached at the center. The
venation is palmate with four, sometimes five, primary veins. One
primary has pinnate secondaries while the others, grouped proximally,
branch dichotomously. The primaries and secondaries curve to form
brochidodromous loops. The tertiaries are variable and intergrade with
the quaternaries in a reticulate to random reticulate manner. The
affinities to the nymphaeoids is based on the peltate attachment, leaf
shape, leaf architectural characters, and the apparent aquatic nature
of the leaves and stems. The shape of the leaf and the aquatic shoots,
as opposed to rhizomes, are restricted to the Cabombaceae clade. The
minimum ages for both groups of fossils are Albian. Yet molecular
phylogenetic analyses of living members suggest that the two clades
diverged within the Nymphaeales after a long period of shared
ancestry. This is in contrast to the ITA clade and the Chloranthaceae,
both which have shorter stems of molecular divergence and greater
divergence of the individual end members. This may have importance
implications for reconciling molecular clock results and the
differences among molecular and morphological phylogenies.
Key words: Cabombaceae, fossil, Lower Cretaceous, molecular evolution, Nymphaeales, phylogeny