Cheatgrass (Bromus tectorum) is an annual grass that has aggressively invaded the United States in the past few centuries. The grass is native to Eurasia and parts of Africa and entered North America as early as the late 1700s. At least eight different introductions into the Unites States are documented. Cheatgrass has caused dramatic changes in rangeland landscape by changing the native plant biomass distributions. The successful evolution and invasion of cheatgrass into the United States is significant because B. tectorum’s homozygous genome and self-replication are thought to be disadvantageous. We researched earliest known specimens of cheatgrass by county according to herbarium records and literature selections for the entire continental United States. Using ESRI ArcGIS we mapped distribution according to earliest known specimens. Information on coevolution was collected from literature and synthesized by the evolution class. Cheatgrass in the United States is genetically dissimilar to its native range in Eurasia due to multiple introductions from different areas. Preliminary analysis shows that cheatgrass is distributed over ranges geographically similar to its respective original habitat in Eurasia or Africa. The spread of cheatgrass into rangelands has provided strong selection pressure on native plants, resulting in many coevolutionary changes.

Geography and Evolutionary Change of Cheatgrass (Bromus tectorum) in North America