Fritsch, Peter W. , Schiller, Anja M. , Cruz, Boni C. , Davis, Edith L. .
Taxonomic implications of morphological and molecular variation in Cercis canadensis (Fabaceae) from Mexico and Adjacent parts of Texas.
Taxonomic treatments of Cercis canadensis recognize one species (C. canadensis) with variety canadensis, widespread throughout the eastern United States, and varieties texensis and mexicana, found east and west of the Pecos River in Texas, respectively. The distribution of Cercis continues southward into northeastern Mexico, but complex variation in leaf shape has confounded straightforward application of varietal names to the Mexican plants. To clarify the taxonomy of Cercis in Mexico, we conducted a morphometric analysis with 281 herbarium specimens, including a representative set of samples from Texas. Correlation and principal component analysis of 12 characters recovered two groups that correspond to the presence versus absence of branchlet pubescence. These groups are geographically distinct at the northern and southern extremes of the focus area but exhibit a large central region of overlap in Mexico. No other discontinuities in character states were discovered to corroborate this division. Leaf shape varies continuously from ovate-acuminate at the northern and southern extremes to subreniform in the central region, suggesting clinal adaptation to the mesic versus xeric environments in which the plants occur. DNA sequence data from five genic regions (ITS, ndhF, rpoB-trnC, trnD-trnT, and trnS-trnG) that included ten samples of C. canadensis from the eastern U.S. and Mexico support the monophyly of this species. Molecular variation is compartmentalized geographically, with all U.S. samples forming a clade and the Mexican samples unresolved, but is not correlated with branchlet pubescence. Thus our data suggest that, despite high morphological variation, taxonomic entities are not warranted within C. canadensis. Definitive evidence will nonetheless require a larger sample size and data in which morphological and molecular variation are collected for each individual.
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1 - California Academy of Sciences, Department of Botany, 55 Music Concourse Drive, Golden Gate Park, San Francisco, CA, 94118-4503, USA
2 - Wellesley College, Biological Sciences, 106 Central St., Wellesley, MA, 02481, USA
Presentation Type: Oral Paper:Papers for BSA Sections
Location: Maybird/Cliff Lodge - Level C
Date: Monday, July 27th, 2009
Time: 8:15 AM