1. Department of Biology, Colorado State University; Fort Collins, Colorado 80523-1878 U.S.A.
2. Environmental Genetics & Genomics Laboratory; Department of Biological Sciences, Northern Arizona University; Flagstaff, Arizona 86011 U.S.A.
3. Department of Botany; MRC 166, P.O. Box 37012 Smithsonian Institution, Washington, D.C. 20013-7012 U.S.A.