Systematics Section / ASPT
Magallón, Susana .
From fossils to molecules: integrating morphological and molecular data to investigate floral evolution in Hamamelidoideae (Hamamelidaceae).
Hamamelidoideae, a monophyletic group within Saxifragales, comprises 22 living genera and several well-substantiated Cretaceous and Tertiary representatives that vary in their expression of an eudicot floral groundplan characterized by a bipartite perianth and pentamerous merosity. I explore methods to integrate molecular and morphological characters of living and fossil taxa in phylogenetic analysis, and use resulting hypotheses to investigate floral evolution in Hamamelidoideae. Trees obtained from parsimony and maximum likelihood analyses of a four-gene data set for a nearly complete generic representation of Hamamelidoideae and outgroups are very similar, and several of their branches are strongly supported. The tree obtained from parsimony analysis of 55 floral characters mostly agrees with traditional classification, and fossils are placed as sisters to living genera. However, it is weakly supported and significantly incongruent with molecular data and trees. Two alternatives to integrate molecular and morphological data in phylogenetic analysis were implemented. First, total evidence parsimony analyses were conducted for taxa with molecular characters, taxa lacking molecular characters but with a complete morphological set (two living genera), and taxa with an incomplete morphological set (three fossils). The tree from the first total evidence analysis (TE1) is well supported and similar to the molecular trees. However, as taxa with fewer characters were added, resolution within Hamamelidoideae decreased. Second, a morphological parsimony analysis, in which strongly supported clades in TE1 were implemented as constraints, was conducted for the full taxonomic sample. The resulting tree is well resolved, and clade membership of taxa lacking molecular characters was identified. This tree was used to investigate floral evolution. The eudicot floral groundplan evolved at least three times within Hamamelidoideae, however, its elements display distinct evolutionary histories: whereas pentamery evolved three times, the bipartite perianth is plesiomorphic and was lost two times. The evolution of other floral characters will be discussed.
1 - Universidad Nacional Autónoma de México, Department of Botany, Circuito Exterior, Anexo al Jardín Botánico, A.P. 70-233, Mexico City, 04510, Mexico
core eudicot floral groundplan
Presentation Type: Paper
Location: Cottonwood C (Snowbird Center)
Date: Wednesday, August 4th, 2004
Time: 4:30 PM