Recent Topics Posters
Silveira, Michael , Bilodeau, Monica , Simpson, Michael .
Taxonomy of The Flowering Plant Calyptridium (Portulacaceae).
CALYPTRIDIUM is a genus of flowering plants, native to the southwestern U.S. and northwestern Mexico. The species Calyptridium parryi and Calyptridium monandrum are thought to be each other's closest relative, the two differing only in fruit length relative to outer sepal length. C. parryi has been classified most recently into four varieties: arizonicum, hesseae, nevadense, and parryi. These varieties have traditionally been separated from one another based on size and sculpturing pattern of the seeds and shape of the abaxial sepal subtending the fruits. The purpose of this study is to quantify seed size and sculpturing, sepal shape/size, and fruit size of the four varieties of Calyptridium parryi and of Calyptridium monandrum in order to evaluate their taxonomy and biogeography. A graph of the seed diameter versus papillae coverage shows that the four varieties are statistically significantly different from one another in these features. Calyptridium monandrum overlaps with C. parryi vars. hesseae and nevadense in seed size and sculpturing features. The fruit length to sepal length ratio of C. monandrum is significantly greater than any variety of C. parryi; however, the actual sepal length of C. monandrum is significantly smaller. Analysis of the outer sepal length:width ratio shows some differences between taxa. We propose that Calyptridium parryi var. arizonicum be elevated to species status, as this taxon is significantly different (with little to no overlap) from C. monandrum and the three C. parryi varieties in seed size, seed sculpturing, sepal morphology. Although the three remaining varieties of C. parryi (vars. hesseae, nevadense, and parryi) show some differences in seed and sepal features, the occurrence of occasional intermediates and overlap of geographic range indicate that these taxa are best kept as varieties at this time. Future detailed molecular studies may clarify phylogenetic relationships among these taxa and help elucidate speciation mechanisms.
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1 - San Diego State University, Department of Biology, San Diego, CA, 92182, USA
Presentation Type: Recent Topics Poster
Location: Auditorium/Bell Memorial Union
Date: Tuesday, August 1st, 2006
Time: 12:30 PM