Flora of Zapata County, Texas.

Zapata County is located in the western part Of the Rio Grande Plains in southern Texas (US.A.). Most of the vegetation consists of Tamaulipan thornscrub with small areas that support plants characteristic of the South Texas Sand Sheet. The most significant threat facing the native vegetation is the spread of introduced nonnative grasses. No previous effurts to conduct a Boris tic survey of the county have been made. A total of 561 taxa of vascular plants in 330 genera and 91 families were identified as occurring in the county. The largest families are Asteraceae (74 species), Poaceae (74 species), Fabaceae (53 species), Euphorbiaceae (28 species), Malvaceae (22 species), Verbenaceae (20 species), Amaranthaceae (18 species), Onagraceae (17 species), Cactaceae (16 species), Solanaceae (16 species), and Brassicaceae (15 species). One species, Houstonia correllii,'s endemic to Zapata County. Two federally listed endangered species, Pbysaria tbamnopbylla and Tbymopbylla tepbroleuca, occur in the county. There are 18 additional taxa that are of conservation concern. Non-native taxa make up 7 percent of the flora. [ABSTRACT FROM AUTHOR]