2004 American Bryological and Lichenological Society, Botany 2004, Snowbird, Utah. "Studies on the Lichen Species Parmotrema rigidum from Northand SOuth America." (with Robert Harms and Todd Widhelm)
2004 Universidad de San Carlos de Guatemala, Escuela de Biología, “Introducción a los Líquenes,” May 24, 2004.
2003 University of Nebraska-Lincoln, Department of Plant Pathology, “After 35 Years, Some Lichen Stories” March 11, 2003.
2001 American Bryological and Lichenological Society, Botany 2001, Albuquerque, New Mexico. "Lichens of the Ponderosa Pine Forests of Nebraska" (with Sara Morgan)
1992 Nebraska Academy of Sciences, Nebraska Wesleyan University, Lincoln, Nebraska, "Saxicolous Lichen Species Transplanted from Colorado to Omaha, Nerbaska" (with Bradley Schroeder)
1986 Nebraska Academy of Sciences, Nebraska Wesleyan University, Lincoln, Nebraska, "Lichen Flora of Eastern Nebraska Riparian and Adjacent Bluff Forests" (with Teresa L. Cherney)
1984 American Institute of Biological Sciences, Ft. Collins, Colorado, "Progress on the Fifth Checklist of the Lichens of the Continental United States and Canada"
1982 Nebraska Academy of Sciences, Nebraska Wesleyan University, Lincoln, Nebraska, "The Lichen Flora of Costa Rica: Progress and Problems"
1981 Nebraska Academy of Sciences, Nebraska Wesleyan University, Lincoln, Nebraska, "Ecological Studies on the Lichens of the Big Thicket National Preserve, Texas. I. Relationship Between Species Diversity and Host-Tree Trunk Diameter"
1981 Annual Meeting of the American Bryological and Lichenological Society, Highlands, North Carolina, "Parmotrema arteagum, a New Species from West-Central Mexico"
1983 Nebraska Academy of Sciences, Nebraska Wesleyan University, Lincoln, Nebraska, "A New Species of Ramalina from Missouri"
1980 Nebraska Academy of Sciences, Nebraska Wesleyan University, Lincoln, Nebraska, "Studies on the Lichen Flora of West Texas"
1980 BOTANY 80. Joint Meeting of American and Canadian Botanical Societies at the University of British Columbia, Vancouver, British Columbia, "Studies on the Lichen Family Parmeliaceae in Texas: Progress and Problems"
1978 Texas Academy of Science. Lubbock, Texas, "SYSTEM 2000: An Alternative to SELGEM for Herbarium Data Management"
1978 Southwestern Association of Naturalists, Albuquerque, New Mexico, "The Alpine Lichens of New Mexico"
1977 Texas Academy of Science, Baylor University, Waco, Texas, "Studies on the Lichens of the Big Thicket National Preserve, Texas"
1977 American Institute of Biological Sciences, East Lansing, Michigan, "Studies on the Lichen Genus Speerschneidera Trev." 1976 Texas Academy of Science, College Station, Texas, "The Lichen Genus Xanthoparmelia"
1976 American Institute of Biological Sciences, New Orleans, Louisiana, "The Lichen Flora of Texas: Historical Aspects"
1970 AAAS, Southwest and Rocky Mountain Division, Las Vegas, New Mexico, "The Lichen Flora of New Mexico: Historical Aspects"
1968 AAAS, Southwest and Rocky Mountain Division, Colorado Springs, Colorado, "Alpine Lichens from Mt. Audubon, Boulder County, Colorado"