[Photo: Sue Emery, US Fish and Wildlife Service]

Texas Wild-rice
Zizania texana

Description: Texas wild-rice is an aquatic, perennial grass, similar in appearance to Northern and Southern wild-rice. Texas wild-rice is 3.2-6.5 feet (1-2 m) long and usually immersed and lying flat in swift, flowing water. In slow water, the plant is more emergent. Leaves are elongate, linear, and green, ranging from 4.8-44 inches (12-110 cm) long and 0.2-1 inch (0.5-2.5 cm) wide. This plant flowers in spring and fall, although it may occur throughout the year in warm weather. Seeds are cylindrical, black, brown, or green in color, and 4.3-7.6 mm long by 1-1.5 mm wide.

Life History: Texas wild-rice occurs in the upper portion of the San Marcos River with pondweed, wild celery, arrowhead, hydrilla, hornwort, elodea, and water primrose. Texas wild-rice reproduces both sexually and asexually via seeds or stolons. Currently its primary means of reproduction is asexual because of inhibition of sexual reproduction due to unsuitable environmental conditions. Texas wild-rice is wind pollinated.

Habitat: Texas wild-rice prefers to grow in the swift currents of the spring-fed San Marcos River, away from the banks in shallow water (3.2 feet [1 m] or less). It forms large clumps that are rooted in limestone, sand, or gravel. It prefers a coarse sand substrate with low organic matter. Texas wild-rice is associated with other native species.

Distribution: Zizania texana is found in the upper two miles of the San Marcos River, from just below Spring Lake down to the Interstate 35 bridge, Hays County, TX.

The map below depicts the critical habitat for this species, as designated by the US Fish and Wildlife Service pursuant to the Endangered Species Act.

NOTE: No warranty is given, expressed or implied, as to the accuracy, reliability, or completeness of these data. Data do no represent a legal description of the critical habitat boundary; refer to the textual description in the appropriate final rule for this species as published in the Federal Register.

Federally Designated Critical Habitat for Texas Wild-rice (Zizania texana) [Figure: Houston Advanced Research Center using US FWS data]

Status: Texas wild-rice is a state and federally listed (1978) endangered species. There is a refugium for this species at the San Marcos National Fish Hatchery and Technology Center. Dam construction and urban development around the San Marcos River have caused changes in the turbidity, sedimentation, and depth of the river. In addition, growth of invasive species and drawdown of the spring have caused slower current velocities in the San Marcos. The US Fish and Wildlife Service defined the flow required for take as 100 cubic feet per second or less. These habitat changes constitute a serious threat to the one remaining population of Texas wild-rice. Other concerns are herbivory by nutria and waterfowl, as well as impacts of recreationists, (i.e. tubers and swimmers).

Resources:

Poole, Jackie and Bowles, David E. 1999. Habitat characterization of Texas Wild-rice (Zizania texana Hitchcock), an endangered aquatic macrophyte from the San Marcos River, TX, USA. Aquatic Conservation: Marine Freshwater Ecosystems. Vol. 9, pp 291-302.

Power, Paula. 1997. Moisture, Seeds, and Reproductive Failure in Texas Wildrice (Zizania texana). The Southwestern Naturalist. Vol. 42, No. 4, pp. 435-440.

Texas Parks and Wildlife, Endangered Species Profile

US Fish and Wildlife Service, San Marcos Recovery Plan