DEPARTMENT OF BOTANY
Mexican Boundary Survey
The Mexican Boundary Survey
The Mexican Boundary Survey was the most comprehensive vegetative investigation ever conducted on the 1,969 mile border between Mexico and the United States. The U.S. government commissioned the survey in order to map and mark the new boundary that resulted from the 1848 Treaty of Guadalupe Hidalgo. The government also commissioned several naturalists to gather plant and animal specimens in order to understand the natural resources of the area.
Many botanists took part in different legs of the Survey, including William H. Emory, Charles Christopher Parry, Charles Wright, George Thurber, Arthur Schott, and John Bigelow. After the expedition, the botanists then sent their specimens to John Torrey, George Engelmann, and Asa Gray, botanists who catalogued the collection and named the new species. Torrey described the rareness of the plants of the El Paso and Rio Grande Valley, writing that, “Upon the tablelands which spread out beyond the mountain barrier, the eye falls upon a great variety of plants, none of which are seen in a more fertile valley.”
The “Report on the United States and Mexican Boundary Survey” is comprised of descriptions of plants and plates of illustrations. Pilostyles thurberi, or Thurber’s stemsucker, was described in the report and is one of southern California’s rarest wildflowers. Thurber found the parasitic plant growing on a new species of dalea (Psorothamnus emoryi) in a small area near the Salton Sea . P. thurberi, with its tiny purple-brown flowers that are less than a sixteenth of an inch wide, was a shocking discovery for the botanists of the day. It is the only North American relative of the parasite Rafflesia, a putrid smelling plant that produces the single largest flower in the world and grows in Southeast Asia.
Torrey states that, in the El Paso and Rio Grande Valley, “the Cacti flourish in a congenial soil.” Engelmann wrote an entire book about the cacti family entitled “Cactaceae of the Boundary,” in which he describes Engelmann’s thistle Cirsium engelmanni and the prickly pear Opuntia erinacea. Engelmann explains that the genus Opuntia, “is distinguished from the other Cactaceae by its barbed spines which [I] [do] not find in any other plant of this family.” He also notes that the barbed spines separate from their stem and easily attach to clothes and skin of anyone walking by, calling them “the most annoying burs.”
The expedition discovered numerous plants that were new to the boundary area and even some that were new to science completely. Many of the new species discovered on the Mexican Boundary Survey were named after its main participants. Torrey and Engelmann named the lotebush Ziziphus parryi and the cane cholla Opuntia parryi after Parry. Torrey leant his name to the famous Torrey Pine Pinus torreyana, Bergerocactus emoryi was named after Emory, and Echinocereus engelmannii was named after Engelmann. Thurber, a botanist who participated in some of the later years of the survey, leant his name to the genus Thurberia, which includes the species Thurberia thespioides. The Mexican Boundary Survey provided a more extensive listing of plant species along the United States-Mexican border than had ever been created before, and was an important contribution to botanical knowledge.
Chester, Tom. "Plants of Southern California: Pilostyles." Table of Contents for all of Tom Chester's webpages. http://tchester.org/plants/ analysis/pilostyles/index.html.
Beidleman, Richard G. California’s Frontier Naturalists. Los Angeles: University of California Press, 2006.
Shaw, Elizabeth A. Charles Wright on the Boundary 1849-1852. Westport, CT: Meckler Publishing Corporation, 1987.
Engelmann, George. Cactaceae of the Boundary.
Torrey, John. United States and Mexican Boundary Survey.
Utley, Robert Marshall. Changing Course: The International Boundary, United States and Mexico, 1848-1963. Tucson: Southwest Parks and Monuments Association, 1986.