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Systematics Section / ASPT

Windham, Michael D. [3], Al-Shehbaz, Ihsan [4], Bailey, C. Donovan [1], Allphin, Loreen [2].

A Taxonomist’s Worst Nightmare: a Preliminary Glimpse into the Systematics of Boechera (Brassicaceae).

Nearly 30 years ago, Askell and Doris Löve proposed Boechera as a North American segregate of the cosmopolitan genus Arabis. Although consistently separated by chromosome base number (x = 7 in Boechera vs. x = 8 in true Arabis), morphological distinctions between the two taxa are subtle and the treatment of Boechera as a distinct genus has not been widely accepted. However, ongoing molecular studies involving both chloroplast and nuclear genes indicate that Boechera is phylogenetically isolated from Arabis and more closely related to Halimolobus, Capsella, and Arabidopsis. On the basis of these data, most of the North American species of Arabis recently have been transferred to Boechera. We have initiated a detailed study of this group in preparation for the Flora of North America and, in the process, found ourselves in the midst of a taxonomic nightmare. Molecular data suggest that Boechera appeared on the scene rather recently, probably within the last two million years. Over this relatively short period, divergent speciation has produced at least 40 morphologically distinct, sexual diploids. However, reproductive isolation has not kept pace with morphological divergence in this group, and the diploids appear to hybridize whenever they come into contact. These hybridization events have given rise to a diverse array of facultatively apomictic diploids and obligately apomictic triploids and tetraploids that bridge the morphological gaps among otherwise discrete diploids. On the positive side, Boechera is rich in morphological features that hold great promise for determining the parentage of most hybrid taxa. It is hoped that a thorough morphological reassessment, done in concert with cytogenetic, reproductive and molecular analyses, will one day yield a workable, phylogenetically congruent classification of Boechera.

1 - New Mexico State University, Department of Biology, P.O. Box 3001, Dept. 3AF, Las Cruces, New Mexico, 88003-8001, USA
2 - Brigham Young University, Department of Integrative Biology, P.O. Box 5181, Provo, Utah, 84602, USA
3 - University of Utah, Utah Museum of Natural History, 1390 E. President's Circle, Salt Lake City, Utah, 84112-0050, USA
4 - Missouri Botanical Garden, PO Box 299, St. Louis, Missouri, 63166-0299, USA


Presentation Type: Paper
Session: 38-12
Location: Cottonwood A (Snowbird Center)
Date: Tuesday, August 3rd, 2004
Time: 5:00 PM
Abstract ID:650

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