Covered Species Information
Authored by Connor Helsel
Texas wild-rice (Zizania texana) is found only in one aquatic habitat, the upper reaches of the San Marcos River in Hays County, Texas (Poole & Bowles, 1999). Human activities caused a decrease in the population of Texas wild-rice prior to its federal listing in 1978. River bottom dredging, plant collecting for aquarium trade business, the introduction of non-native aquatic species, and wastewater pollution posed threats to the survival of the species (Emery, 1967).
Beginning in 2013, the City of San Marcos, in partnership with Texas State University, implemented a Texas wild-rice enhancement and restoration program that works to remove non-native aquatic vegetation and plant Texas wild-rice in its place. The program has been very successful – with the coverage of Texas wild-rice increasing 129% from the summer of 2013 (5,019 m2) to summer of 2019 (11,495 m2; BIO-WEST, 2014; BIO-WEST, 2019).
Endangered Species Act status
Culms, or stems, grow to 3 m (9.84 feet) long when underwater and 1 to 2 m (3.58-6.58 feet) when partially immersed, with linear leaves reaching 1 m (3.28 feet; Terrell et al., 1978).
Physical description and Life History
A member of the Poaceae family, Texas wild-rice is a perennial aquatic grass that produces clumps of immersed, ribbon-like leaves that sway with stream flow (Poole & Bowles, 1999; Terrell et al., 1978). Texas wild-rice reproduces both sexually and asexually. Emergent Texas wild-rice stands can sexually reproduce by seedlings and submergent Texas wild-rice stands can asexually reproduce by runners, or small vegetative clones of itself (Power & Oxley, 2004; Richards et al., 2007).
Other, often non-native, aquatic vegetation can outcompete Texas wild-rice for resources and take over available habitat. Large planting efforts work to restore a balance of species diversity so that Texas wild-rice is not edged out by invasive species (National Academies of Sciences, Engineering, and Medicine, 2018).
Texas wild-rice is found in the upper 4 km (2.49 miles) of the San Marcos River in Hays County, Texas (Poole & Bowles, 1999).
Texas wild-rice prefers shallow water of 1 m or less with moderate to fast current and coarse substrate (Poole & Bowles, 1999).
Maintaining constant spring water temperature is a key component to Texas wild-rice persistence since an internal leaf temperature of over 25°C has shown to impact photosynthesis, leading to energy loss and leaf die off (Poole & Bowles, 1999; Richards et al., 2007).
Beaty, H. E. (1975). Texas wild-rice. Texas Horticulturist, 2, 9–11.
BIO-WEST, Inc. (2014). Habitat Conservation Plan Biological Monitoring Program San Marcos Springs/River Ecosystem. Annual Report prepared for Edwards Aquifer Authority. 232.
BIO-WEST, Inc. (2019). Habitat Conservation Plan Biological Monitoring Program San Marcos Springs/River Ecosystem. Annual Report prepared for Edwards Aquifer Authority. 58.
Blanton & Associates, Inc. (2020). Edwards Aquifer Habitat Conservation Plan 2019 Annual Report. https://www.edwardsaquifer.org/wp-content/uploads/2020/03/2019-EAHCP-Annual-Report.pdf
Emery, Wm. H. P. (1967). The Decline and Threatened Extinction of Texas Wild Rice (Zizania texana Hitchc.). The Southwestern Naturalist, 12(2), 203. https://doi.org/10.2307/3669290
Hitchcock, A. S. (1933). New species and new names of grasses from Texas. Journal of the Washington Academy of Sciences, 23(10), 9.
National Academies of Sciences, Engineering, and Medicine. 2018. Review of the Edwards Aquifer Habitat Conservation Plan: Report 3. Washington, DC: The National Academies Press. https://doi.org/10.17226/25200
Poole, J., & Bowles, D. E. (1999). Habitat characterization of Texas wild-rice (Zizania texana Hitchcock), an endangered aquatic macrophyte from the San Marcos River, TX, USA. 13.
Power, P., & Oxley, F. M. (2004). Assessment of Factors Influencing Texas Wild-Rice (Zizania Texana) Sexual and Asexual Reproduction.
Richards, C. M., Antolin, M. F., Reilley, A., Poole, J., & Walters, C. (2007). Capturing genetic diversity of wild populations for ex situ conservation: Texas wild rice (Zizania texana) as a model. Genetic Resources and Crop Evolution, 54(4), 837–848. https://doi.org/10.1007/s10722-006-9167-4
Terrell, E. E., Emery, W. H. P., & Beaty, H. E. (1978). Observations on Zizania texana (Texas Wildrice), an Endangered Species. Bulletin of the Torrey Botanical Club, 105(1), 50. https://doi.org/10.2307/2484263