Perplexity of The Walker's Manioc!

An endangered plant in Texas

Life History

Historically, Walker's manioc is known only from the lower Rio Grande valley of Texas (Hidalgo and Starr counties) and northern Tamaulipas, Mexico. Until recently, it was believed that this species was represented in the U. S. by a single plant in the wild, discovered in Hidalgo County in 1990. In 1995, Walker's manioc was located in three different areas on the Lower Rio Grande National Wildlife Refuge in Starr and Hidalgo Counties.

Walker's manioc is a member of the spurge family (Euphorbiaceae) and is related to the important crop plant, cassava, an important source of starch and a staple food for peoples of the tropics worldwide. Little is known concerning the biology of Walker's manioc. The landowner protecting the one plant growing on private land in Hidalgo County reports that the white flowers open in clusters of three or four fragrant blossoms in late afternoon and last only one day. Specific pollinators have not yet been determined.
The importance of Walker's manioc as a genetic resource highlights the need to protect this species. Because Walker's manioc may contain genes that provide resistance to drought, cold, or plant disease, and compounds that are useful for treating human disease, it is of special interest to botanists, plant breeders, and drug companies. If Walker's manioc and cassava can be interbred, it may be possible to reduce crop diseases or expand the range over which cassava can be grown, helping to feed more people.

Location of the Walker's Manioc

The Fate of the Manioc

Threats to the Walker's Manioc

Many of the plants recently found in the wild are growing within another shrub and therefore are very difficult to see. Walker's manioc plants may be defoliated and die back to tubers in response to prolonged drought, freezing weather, or excessive grazing. They grow in association with anacahuita, barreta, blue sage, Calderona krameria, cenizo, coyotillo, drago, elbowbush, guayacan, tasajillo, and wild oregano. Much of the native brush habitat in the historical range of Walker's manioc has been cleared for agriculture, urbanization, or improved pasture. It has been estimated that over 95% of the native brush in the Lower Rio Grande Valley has been converted to other land uses.

Actions to Help Save the Walker's Manioc

As part of efforts to recover this species, transplanted specimens are under cultivation at the University of Texas, Austin and at the San Antonio Botanical Gardens. Landowners and land managers can help conservation efforts by learning to recognize this rare and potentially important plant, and by protecting the area where it grows from land use changes. Mechanical brush management and herbicide use should be carefully planned to avoid impacts to these sites.