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Native Plant Society of Texas

Plant Defense: The Eternal Battle with Animals and Pathogens

Presentation Details

Plants have evolved a large number of defense mechanisms by which they defend themselves. However, animals are constantly evolving to get around these tactics. The result is that plants and animals (and pathogens) are constantly in a coevolutionary arms race. Some of the plant mechanisms include physical defense, chemical defense, animal guard defense, and escape in time or space.

Many animals in Texas, especially livestock, are affected adversely by toxins each year. Even people are impacted negatively by certain plants that they incorrectly think are healthy for them to eat.

Equipment Required:
None
Additional Requirements:
None
Ecoregions Covered:
Central Great Plains, Chihuahuan Deserts, Cross Timbers, East Central Texas Plains, Edwards Plateau, Gulf Coast Prairies and Marshes, High Plains, Southern Texas Plains, Southwestern Tablelands, Texas Blackland Prairies, Western Gulf Coastal Plain

Presenter Information

George Diggs

George Diggs is an evolutionary biologist and botanist who has taught for more than 40 years at Austin College in Sherman, and a Research Associate at the Botanical Research Institute […]

  • George Diggs

    George Diggs is an evolutionary biologist and botanist who has taught for more than 40 years at Austin College in Sherman, and a Research Associate at the Botanical Research Institute of Texas.

    His research interests include the plants of Texas, evolution as it relates to human health, the systematics of the Ericaceae (Blueberry Family), and biogeography.

    He has co-authored four books, including The Ferns & Lycophytes of Texas, co-authored with Barney Lipscomb, and more than 30 scientific articles. In his research he has traveled to all seven continents. He helped found the Public Health program at Austin College and teaches Environmental and Evolutionary Health, including the impact of diet and toxins on human health.
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About the Region

New Braunfels, the location of our Fall 2024 Symposium, straddles both the Edwards Plateau Ecoregion and the Blackland Prairie ecoregion. Interstate 35 divides the city of New Braunfels; its path through the city closely parallels the boundary of these two ecoregions, with the Edwards Plateau on the west side and the Blackland Prairies region to the east. The Edwards Plateau area is also called the Hill Country; however, this general term covers a much larger area extending farther north. Spring-fed creeks are found throughout the region; deep limestone canyons, rivers, and lakes (reservoirs) are common. Ashe juniper is perhaps the most common woody species found throughout the region. Additional woody species include various species of oak, with live oak (Quercus fusiformis) being the most common. Sycamores (Platanus occidentalis) and bald cypress (Taxodium distichum) border waterways. This area is well known for its spring wildflower displays, though they may be viewed in spring, late summer, and fall, as well. According to Texas Parks and Wildlife, average annual rainfall in the Edwards Plateau ranges from 15 to 34 inches.

The Blackland Prairie extends from the Red River south to San Antonio, bordered on the west by the Edwards Plateau and the Cross Timbers, and on the east by the Post Oak Savannah. Annual rainfall averages 30 to 40 inches, with higher averages to the east. This region is dominated by prairie species. The most common grass species include little bluestem (Schizachyrium scoparium) and Indian grass (Sorghastrum nutans) in the uplands and switchgrass (Panicum virgatum) in the riparian areas and drainages. Common herbaceous flowering plants include salvias, penstemons, and silphiums. This area has suffered greatly from overgrazing and agricultural use. Few intact areas remain, though many of the plants can be found along county roadsides throughout the region.

Our four host chapters (New Braunfels, Lindheimer, Guadalupe, and the Hill Country chapters) are located in one or both of the ecoregions above. However, the eastern portion of Guadalupe County also falls within the Post Oak Savanna ecoregion. Annual rainfall averages 35 to 45 inches, with higher averages to the east. A wide variety of hardwood trees are found, including several species of oaks, elms, and in the Bastrop area, loblolly pine (Pinus taeda). Grasses and forbs dominate in the open savannas, with most common grass being little bluestem. Ranching, agriculture, and fire suppression have allowed woody species to encroach on the once-open savannas.

Source: Wildflowers of Texas by Michael Eason