Angiosperm wood evolution and the potential contribution of paleontological data |
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Authors: | Patrick S Herendeen Elisabeth A Wheeler Pieter Baas |
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Institution: | (1) Department of Biological Sciences, The George Washington University, Lisner Hall 340 2023 G Street NW, 20052 Washington, DC, USA;(2) Department of Wood and Paper Science, North Carolina State University, 27695 Raleigh, NC, USA;(3) Rijksherbarium/Hortus Botanicus, P.O. Box 9514, 2300 RA Leiden, The Netherlands |
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Abstract: | Wood anatomy is often viewed as a source of independent data that may be used to assess evolutionary relationships among angiosperms.
Comparative anatomical studies document suites of correlated characters that have been interpreted as general evolutionary
trends, of which several have been asserted to be irreversible. Paleobotanical data summarized by Wheeler and Baas provide
broad chronological corroboration of some wood anatomical trends, such as evolution from scalariform to simple perforation
plates and long to short vessel elements. However, the focus on general evolutionary trends rather than on analyzing character
distribution patterns in a cladistic phylogenetic context obscures a more detailed understanding of the evolution of wood
anatomical features. Patterns of character evolution, including the assertions of irreversibility, need to be tested through
cladistic analyses. In this paper selected wood anatomical features from families of Magnoliidae and “lower” Hamamelididae
are summarized and mapped onto previously published cladograms as a preliminary means of testing previous hypotheses of wood
evolution. The results show that many of the characters are homoplasious and have evolved both in accord with, and counter
to, the hypothesized general trends in different groups of flowering plants. In general, changes that confirm generalized
trends are more common than changes that are counter to those trends. Future studies should combine wood anatomical characters
with other features as part of a cladistic analysis. Fossil woods have not yet contributed significantly to phylogenetic studies,
but in the very few cases where they have been linked to fossil reproductive structures, the woods have provided a better
understanding of wood anatomy in early members of some families. Data from fossil wood expand the diversity of anatomical
structure known in some angiosperm taxa and thus provide additional evidence that might be used in phylogenetic analyses.
Fossil woods have the greatest potential to affect phylogenetic analyses where they can be linked to other fossil organs.
The best chance for establishing such a linkage is through the study of fossil charcoalified woods that co-occur with other
dispersed mesofossils. |
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