NatureServe Conservation Status
Rounded Global Status Rank: G1 - Critically Imperiled
Reasons: Endemic to the upper few km of the San Marcos River in south-central Texas, where it was locally abundant as recently as the the 1950s. It is now reduced to a precariously small population covering about 1200 square meters on an urbanized segment of the river. This remnant population rarely flowers or produces seed in the wild. The decline of this grass, which is narrowly adapted to high quality, aquifer-fed waters, is the result of drastic draw-downs in the aquifer level to support human population growth in the area, combined with past dredging and vegetation removal, damming, increased siltation and sewage loads, trampling and removal by recreationists, and herbivory by native and introduced waterfowl and by the non-native nutria. Efforts to establish new populations off the San Marcos River using cultivated plants have not been successful.
Environmental Specificity: Very narrow. Specialist or community with key requirements scarce.
Comments: Restricted to clear, cool, fast-flowing spring water (unusual in south-central Texas).