Overview
Texas wild rice is a submergent aquatic perennial grass with leaves that are 3 to 6.5 feet long. Texas wild rice forms large stands at depths from 0.76 to 3.3 feet and requires clear, relatively cool, thermally constant flowing water of about 72°. Texas wild rice prefers gravel and sand substrates overlaying Crawford black silt and clay. Spring flow is critically important for growth and survival of Texas wild rice. Texas wild rice relies on high levels of carbon dioxide from spring water, for its inorganic carbon source for photosynthesis, rather than the more commonly available bicarbonate, which is used by most other aquatic plants. Low flow situations can be carbon-limiting for carbon dioxide-using obligates, including Texas wild rice.
Texas wild rice is only found in the San Marcos River. Texas wild rice was listed as endangered on April 26, 1978 (43 FR 17910). Reduced spring flow is the greatest threat to the survival of Texas wild rice. Other threats include water quality degradation, physical alteration of Spring Lake or the San Marcos River, physical disturbance of the species and non-native species. We work with our partners to ensure that the springs and groundwater will continue to provide clean and healthy freshwater to related microhabitats and to support the important life history and biological research to address the needs for the species. Efforts are underway by partners to reduce non-native vegetation in the river.
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Characteristics
Life Cycle
Texas wild ricecan reproduce either asexually, also referred to as clonally, through stolons or sexually, via seeds. Asexual reproduction occurs where shoots arise as clones at the ends of rooting stolons. Clonal reproduction appears to be the primary mechanism for expansion of established stands, but does not appear to be an efficient mechanism for dispersal and colonization of new areas. Texas wild rice segments have, however, been observed floating downstream and some of these may become established plants if they become lodged in suitable substrate and physical habitat.
During sexual reproduction, Texas wild rice flowers above the water surface and wind pollinated florets produce seed. This typically takes place in late spring through fall, though flowering and seed set may occur at other times in warm years. The triggers for flowering are not well understood. Texas wild rice seed is not long-lived, and viability begins to drop markedly within one year of production. No appreciable seed bank is therefore expected. In slow moving waters, Texas wild rice functions as an annual. In those cases, plants exhibit less robust vegetative growth, then flowering, setting seed and dying within a single season.
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