Nongame and Rare Species Program: Rare Plant Communities of Texas
Edwards Plateau: Spring Run Vegetation
Global Rank: G2
Description: These communities are narrow in spatial extent, occurring within streams fed by first or second magnitude limestone springs in the Edwards Plateau of central Texas. Examples include stream reaches immediately below San Marcos Springs in Hays County, Comal Springs in Comal County, Robertson Springs in Bell County, and other major springs. Many historical examples (e.g. San Felipe Springs in Val Verde County) have been modified so the natural community is not extant. The globally endangered endemic grass Zizania texana is dominant in the upper 5 kilometers of the San Marcos River, the only place where it occurs. Other emergent, floating, and submerged aquatic plants may include Potamogeton illinoensis, Hydrocotyle verticillata, Ludwigia palustris, Sparganium americanum, Eleocharis cellulosa, Callitriche paploides, Bidens laevis, and filamentous green algae. Introduced species such as Hydrilla verticillata (exotic), Egeria densa (exotic), and Colocasia esculenta (exotic) have become dominant in many sites. These communities are also threatened by overpumping of groundwater, sedimentation, and recreational overuse.