Phytogeography of the woody flora of the lower Rio Grande Valley, Texas

Abstract

The lower Rio Grande Valley (LRGV) of Texas is delimited by distinct physiographic features and its fauna and flora include many species that do not occur elsewhere in the state. The LRGV native woody flora is comprised of 178 species. Sixty-six species (37.1 percent) reach their northern limit of distribution in southern Texas, and 46 of these species also occur in southern Florida. The LRGV woody flora has its greatest affinity (46.1 percent of the species) with the nondesert woody flora of Mexico, but there is a strong representation (37.6 percent) of woody species from southwestern deserts. These two elements comprise 83.7 percent of the LRGV woody flora. There are no species endemic to the LRGV, but 14 species (7.9 percent of the LRGV woody flora) are endemic to the Tamaulipan Biotic Province. Colonization has mainly been from Mexico and areas of humid tropical America (including the Caribbean), southwestern deserts (especially the Chihuahuan Desert), and the Coastal Plain of temperate North America. Dry fruits are the most common propagules. Birds and other animals are the dominant dispersal agents. Key words: phytogeography; Rio Grande Valley; woody plants.