|Listed||April 26, 1978|
|Description||Perennial aquatic grass with grain-like seed heads.|
|Habitat||San Marcos River; cool, fast-flowing, spring-fed water.|
|Threats||Groundwater pumping and diversion, silting, poor reproduction.|
Texas wild-rice, Zizania texana, is an aquatic grass with thin, flat, elongated leaves typically immersed and long-streaming in river currents. Leaves often grow as long as 57 in (145 cm). Flower stalks, when present, extend above the surface of the water, sometimes to a height of 3 ft (1 m), and produce drooping heads of profuse grain-like seeds.
Southern wild-rice is a much more robust plant than Texas wild-rice, attaining heights up to 413 ft (126 m) and having only its lower culms immersed in water; the rest of the plant is erect and emergent. In addition, the leaves of southern wild-rice are 3-5 times as broad as those of Texas wild-rice. In southern wild-rice, the upper inflorescence branches are long and widely spreading, while those of Texas wild-rice are shorter, more erect, and appressed. Southern wild-rice has lemmas and paleas that are thin and papery, while those of Texas wild-rice are somewhat leathery.
Northern wild-rice is somewhat smaller in stature and more closely resembles Texas wild-rice. Distinguishing characters are that the spikelet is generally longer (up 0.8 in [2 cm] long in northern wild-rice, while Texas wild-rice seldom exceeds 0.5 in [1.3 cm]), the paleas and lemmas of northern wild-rice are distinctly leathery, and the lemmas of northern wild-rice have prickle hairs in lines rather than randomly scattered as in Texas wild-rice. The northern wild-rice plants are generally more emergent than Texas wild-rice under typical growing conditions, though in some conditions Texas wild-rice will become more emergent.
The plant flowers and sets seed at irregular intervals from April to November. Seeding plants have become increasingly rare in the wild. Reproduction
Texas wild-rice produces new plants either via seeds or stolons. When reproducing sexually, the long rigid decumbant culm (12 ft [4 m] or more) bends upward at its nodes, emerges above the current, and produces a 8-12 in (20-30 cm) flowering panicle. Asexual reproduction occurs where shoots arise at the ends of stolons. While asexual reproduction has been noted and some plants have produced culms for inflorescences, plants have not successfully been producing (or setting) seed in the San Marcos River. The species is predominantly out-breeding and wind-pollinated. The failure of wild-rice to produce seed in the wild is probably not due to any genetic, cytological, or embryological problems, but rather to some extrinsic factor or factors. Plants grown in raceways at Southwest Texas State University's Aquatic Station successfully bloom and set seed, and seed have been observed to drop in place and subsequently germinate.
The San Marcos River arises in a cluster of springs and seeps along the Balcones Fault, fed by the Edwards Aquifer. Texas wild-rice forms large clones or masses of clones that firmly root in gravel shallows near the middle of the river. This plant is adapted to fast-flowing water of high quality and constant year-round temperature as provided by adequate spring flows. Silting, disturbance of the bottom, or stagnant water will kill off plants.
The plants form large clumps rooted in the limestone sand and gravel river bottom, which overlays Crawford black silt and clay. It also occurs in Spring Lake and its irrigation waterways in both the margins of the stream and in the swiftly flowing currents some distance from the bank. While exotic elephant ears occupy river margins rather than the regions with swift current, hydrilla (which has also been introduced in recent times) forms extensive stands in some swift areas of the river today. The consequences of this to Texas wild-rice are unknown, but it is possible that hydrilla is competing with Texas wild-rice or altering its essential habitat.
Experimental studies have shown that Texas wild-rice grew poorly in Spring Lake at water depths greater than 6.6 ft (2 m) due to decreased light intensity and shading from other aquatic vegetation; robust growth occurred at 5.25 ft (1.6 m) in experimental reintroduction work. Plants did not survive in moist or alternating wet/dry experimental conditions, only in constantly inundated conditions. Plants grown in an artificial raceway environment produced seed at water depths ranging from 7.9-23.6 in (20-60 cm). Other species of wild-rice require very shallow water for germination.
Texas wild-rice seeds germinated more readily under low oxygen conditions and buried seeds (buried in either clay or sand) germinated more readily than seeds at the substrate/water interface. Fewer seeds germinate as storage time increases and, of seeds that germinate, fewer have successful seedling development.
This wild-rice is endemic to the San Marcos River basin of Hays County, Texas. It was once abundant in the San Marcos River, in contiguous irrigation ditches with constant flows, and in Spring Lake at the river headwaters. It was so abundant, in fact, that during the 1930s the local irrigation company considered it a difficult task to keep plants from clogging its ditches.
Since 1989, the Texas Parks and Wildlife Department has been monitoring area coverage, and studies have established that current distribution of Texas wild-rice extends from the uppermost part of the San Marcos River just below Spring Lake dam and throughout the critical habitat down to an area slightly below the wastewater treatment plant, except for the river portion between the Rio Vista railroad bridge and the dam above Cheatham Street.
The major reason for decline of the San Marcos River habitat has been increased pumping and diversion of the groundwater of the Edwards Aquifer. The rate of outflow from the San Marcos springs has decreased, and will continue to decrease, as the human population of the region increases. Decreased spring outflow lowers the water level of the river and exposes the shallows where Texas wild-rice would typically grow. At current levels of human population growth, outflow from the springs may cease altogether around the year 2000.
Conservation and Recovery
Because much of the current population falls within the city limits of San Marcos, botanists have suggested that transplanting wild-rice to some other suitable location is the species' only hope of survival. The Fish and Wildlife Service stresses that every effort must be made to preserve the species in its native habitat; transplanting should be used to supplement the surviving population but not to supplant it.
Repeated efforts to grow Texas wild-rice in cultivation and to transplant it have met with limited success. In the 1970s, botanists at Southwest Texas State University (San Marcos) attempted to establish a new population in Salado Creek with cultivated plants, but recreational activities continually disturbed transplanted clones. From 1976-82, nursery grown plants were unsuccessfully transplanted to various sites in central Texas, including the Comal River (Comal County), and other spring-fed streams in Hays County. The result of these efforts was an increased mastery of seed collection and germination techniques, but no new populations.
In the mid-1980s, a growing program at race-ways at Southwest Texas State University began to reap success. The growth rate was higher in the raceways than in the San Marcos River itself, possibly due to increased light and temperature. In December, 1992, and March and July, 1993, 183 young plants raised in raceways were planted in Spring Lake near the dam. Five-hundred plants were planted on the northwest side of the lake in 1994. Although both reintroduction sites showed a slight increased in stem density during 1994, they later showed a decline. The reintroduction may be jeopardized by competition with other aquatic vegetation and shading by cut vegetation floating downstream.
The Fish and Wildlife Service Recovery Plan and its 1996 revision recommend that a public education program be established, aimed at minimizing recreational disturbance of wild-rice in the San Marcos River. Ultimately, long-term protection of Texas wild-rice and other endemics will require devising a workable management program to balance the water needs of the growing human population with the requirements of a healthy San Marcos River ecosystem. Local, state, and federal agencies will need to cooperate to maintain adequate out-flow from the Edwards Aquifer and sufficient water levels in the river to support a diversity of wildlife.
Delisting is considered unattainable for all five species covered in the revised plan (including Texas wild-rice) due to the potential for extinction from catastrophic events. Consequently, the revised Recovery Plan calls for the establishment and continued maintenance of refugia capability for all five species in case of a catastrophic event. Though delisting is considered unlikely, downlisting is considered a possibility for Texas wild-rice, possibly as early as 2025 if continuous progress is made.
Sustrup, A., and M. C. Johnston. 1977. "Report on the Status of Zizania texana Hitchcock." Rare Plant Study Center, University of Texas, Austin.
U.S. Fish and Wildlife Service. April 26, 1978. "Determination of Texas wild-rice (Zizania texana ) as Endangered" Federal Register 43: 17910-17916.
U.S. Fish and Wildlife Service. 1984. "San Marcos River Recovery Plan." U.S. Fish and Wildlife Service, Albuquerque.
U.S. Fish and Wildlife Service. 1996. "San Marcos and Comal Springs and Associated Aquatic Ecosystems (Revised) Recovery Plan." U.S. Fish and Wildlife Service, Albuquerque.