Systematics/Phytogeography / Taxonomie/ Section
Edson, Thomas , Philbrick, C. Thomas , Jensen, Richard .
Morphometric analyses of leaf form variation in Mexican and Central American Marathrum (Podostemaceae).
As many as 12 species of Marathrum (Podostemaceae) are recognized in Mexico and Central America. For most, species distinctions are purportedly based on variation in leaf features. Such features are difficult to assess qualitatively, however. Leaves of these species are structurally complex, e.g., repeatedly pinnate, with ultimate divisions varying in size and shape. Distinctions among species that possess a whorl of stamens in their flowers, the focus of this study, are especially troublesome (e.g., M. schiedeanum, M. minutiflorum, M. oxycarpum). The present study represents the first application of quantitative methods to assess relationships between leaf form variation and species boundaries. We conducted morphometric analyses of leaf form variation among 30 OTUs (OTU = 1 leaf) representing populations from Mexico, Honduras, and Costa Rica. Fifty-two measurements taken from each leaf were used to evaluate phenetic relationships via cluster analysis (CA) and principal components analysis (PCA). First, the characters were standardized and used to generate a matrix of pair-wise average taxonomic distances for CA. As a complement to this, the matrix of character correlations was used as input for PCA. Second, the characters were log-transformed and then used, as above, for CA. The log-transformed data were used for PCA based on the character variance-covariance matrix. Marathrum tenue, a clearly defined species based on reproductive characters but also possessing complex pinnate leaves, was used as a standard. Results failed to reveal consistent groupings among OTUs. Even OTUs of M. tenue failed to group together consistently. Results of this study support the hypothesis that there is only a single species of Marathrum in Mexico and Central America that possesses pinnate leaves as well as flowers with a whorl of stamens.
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1 - Western Connecticut State University, Biological & Environmental Sciences, 181 White Street, Danbury, CT, 06810, USA
2 - Saint Mary's College, Department of Biology, Notre Dame, Indiana, 46556, USA
Presentation Type: Oral Paper:Papers for Sections
Date: Wednesday, July 30th, 2008
Time: 1:45 PM