Floristic study of the Upper Frio River, Texas
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Vascular plant collections and field data compiled during a one and a half year period for the upper Frio River, Texas, produced a flora that comprises 78 families, 223 genera and 319 species. Vascular plants were collected along the upper Frio River in Real, Uvalde, Medina, and Frio Counties during the fall, spring and summer seasons to create a vouchered record of species occurrence. Plants were collected from eleven sites along the river. The largest families are Poaceae (70 spp.), Asteraceae (41spp.), Cyperaceae (19 spp.), Euphorbiaceae (16 spp.) and Fabaceae (13 spp.). These families encompass approximately 51% of the species represented. Introduced species make up 16.1 % of the flora. These percentages are similar to those of the floras of North Central Texas, Madison County, Robertson County and the La Copita Research Area. A total of 9 species endemic to Texas were collected along the upper Frio River. Throughout the northern portion of the study area there is exposed bedrock with little to no soil within the scour lines of the Frio River. Downstream a layer of soil is present, but it is shallow and composed mostly of gravel. Quantitative data on the spatial distribution, frequency and abundance of plant species was collected using a 25 X 50 cm quadrat located approximately every meter along 25 meter transects. These transects were established at seven of the thirteen locations. The most species rich location was site 3 in Real County with 45 species present at the time the transects were run. Locations 6 and 10 are the most similar of all the sites. The most frequent species were Dichanthium annulatum (Forssk.) Stapf, Phyla nodiflora (L.) Greene and Helenium elegans DC. var. elegans. Rock made up most of the cover at all of the locations with the exception of Site 6 where Dichanthium annulatum made up 24% of the cover.
Swihart, Theresa Irene (2003). Floristic study of the Upper Frio River, Texas. Master's thesis, Texas A&M University. Texas A&M University. Available electronically from