Zizania Texana Research Articles

Evaluating the suppression of Hydrilla verticillata by manual removal and planting natives for small-scale restoration efforts in a spring-fed river

Hydrilla (Hydrilla verticillata) is an invasive aquatic macrophyte found on every continent except Antarctica. Due to the high number of federally listed species in the San Marcos River, Texas, management options for hydrilla are limited. We examined the ability of the two native macrophytes to suppress hydrilla in plots where 0 to 100% hydrilla was removed. In plots where 100% hydrilla was removed, Texas wild rice exhibited equal or greater coverage to hydrilla. Hydrilla was present in 100% of the plots at the end of the study, regardless of percent removal, while Texas wild rice (Zizania texana) and water stargrass (Heteranthera dubia) were present in 50 and 42% of the plots, respectively. While the overall survival percentage in plots was 50% for Texas wild rice, the mean root and shoot dry weights were significantly greater than hydrilla which occurred in all plots. However, hydrilla coverage was among the highest in plots where 100% of the hydrilla was removed at the start of the study, indicating its ability to quickly invade disturbed sites. The study results indicate morphological differences with hydrilla allocating greater biomass into its shoots while Texas wild rice allocates equal amounts of biomass into its shoots and roots.

Zizania texana (Texas wild-rice)

This datasheet on Zizania texana covers Identity, Distribution, Further Information.

A thirty-year assessment of the endangered aquatic macrophyte, Zizania texana, endemic to the upper reach of the San Marcos River in Central Texas, USA

Texas wild rice (Zizania texana Hitchc.) is an endemic, federally endangered aquatic macrophyte known only from the upper San Marcos River in central Texas. Annual surveys of Texas wild rice coverage have occurred for 30 years from 1989 to 2018, documenting the known coverage within its limited range. Texas wild rice exhibited a progressive increase in coverage from 1989 to 2018, but coverage increased following 2013 when plantings began. Based on an autoregressive model, the overall maximum coverage growth rate of Texas wild rice was estimated to be rmax = 0.152 indicating a 15% increase in Texas wild coverage annually if discharge is maintained at an optimum of 3.99 m3 s−1. Significant (P < 0.05) increases in Texas wild rice coverage occurred in six of the seven upper segments of the river, while significant (P < 0.05) decreases occurred in five of the seven lower segments. The maximum discharge recorded during the survey was 175 m3 s−1 in 1998, which resulted in a 15.6% decrease in coverage during the 1999 survey, but Texas wild rice coverage increased during 2000. This endangered macrophyte exhibits resilience and resistance to high discharge events due to its fast growth rates, reproductive plasticity, high root-to-shoot ratios, and a perennial life cycle that contributes to its fast recovery following scouring. Decreased spring flows and associated declining water levels due to increased groundwater water extraction represents the greatest threat to the only known population of Texas wild rice as exposed plants become desiccated and suffer high mortality if the upper reach of the river becomes ephemeral.

Vegetation associations of the endangered fountain darter Etheostoma fonticola

Aquatic vegetation provides many services for aquatic habitats and fish communities. The federally listed fountain darter Etheostoma fonticola, found only in spring systems of the San Marcos and Comal rivers in central Texas, is reported to associate with vegetation for feeding, reproduction, and refuge. Descriptions of associations with vegetation range from preferred to exclusive, whereas other studies describe fountain darters found outside of vegetation. The purposes of this study were to quantify fountain darter occurrences and abundances among vegetated habitats using the concept of obligate and facultative habitat use. Wadeable and non-wadeable habitats among multiple reaches of the San Marcos and Comal rivers were sampled with seines and SCUBA diving methods in the spring and fall from 2014 to 2019. Fountain darters were often associated with aquatic vegetation but demonstrated both obligate and facultative tendencies. Fountain darters occurred in vegetation more than expected among wadeable and non-wadeable habitats in the majority of reaches within the San Marcos and Comal rivers. Among vegetation taxa, they were positively associated with bryophytes and negatively associated with Texas wild rice, but associations with other vegetation taxa varied by river and were possibly influenced by other variables. Current vegetation management in both rivers includes the removal of non-native species and restoration of native vegetation, so understanding the patterns of fountain darter associations with vegetation can guide future management and restoration efforts of these spring systems.

Effects of Photosynthetically Active Radiation on Vegetative Growth of Texas Wild Rice and Consequences for Population Augmentation

As urbanization and urban sprawl increases, habitat for native flora and fauna often becomes threatened. Reestablishing wildlife habitats within designed landscapes has become increasingly popular with horticultural consumers, who are becoming more aware of the benefits of using native plants and the threats of invasive species. Texas wild rice (Zizania texana Hitchc.) is a federally endangered aquatic plant known to occur only in the San Marcos River, Hays County, TX. The objective of this study was to experimentally test the impact of light availability on the vegetative growth of Texas wild rice (TWR) ex situ. The effect of photosynthetically active radiation (PAR) was tested by establishing treatment and control groups of plants in a river raceway located on the campus of Texas State University, San Marcos, TX. At the onset of the experiment, baseline growth data were collected on a random sample of 15 plants to determine starting conditions. The 75 plants within the control and treatment groups were also randomly selected. Two sequential experimental trials were designed involving the same treatment of PAR reductions with 15 TWR plants in the control group (100% of ambient PAR conditions) and 15 within each of four experimental treatment units. Treatments included a reduction in ambient light values at each of the following rates: PAR reduced by 10% (90% ambient light), 20% (80% ambient light), 40% (60% ambient light), and 80% (20% ambient light). Results of the study indicated high shade areas contained reduced areal coverage or complete lack of TWR. There was a significant decrease in both above and below ground biomass, with an 80% reduction in available PAR (20% available ambient light), and other growth parameters of TWR were negatively impacted by reductions in PAR greater than 40% (60% ambient light availability) during the short-term early establishment growth period. Therefore, light availability is a critical environmental factor that must be given consideration when deciding areas of the river to plant TWR for population augmentation.

No evidence of non-target use of native or economic grasses and broadleaf plants by Arundo donax biological control agents

ABSTRACT Two Arundo donax biological control agents, Tetramesa romana, the arundo wasp, and Rhizaspidiotus donacis, the arundo scale, have been established in Texas, USA and Morelos, Mexico for ten years. A survey was conducted in these areas to determine if there was any use of non-target plant species, especially where the biological control agents occurred at high densities. We found no non-target use in examinations of over 1500 plant specimens representing 5 native grasses, 6 introduced grasses, 2 crop grasses, and one broadleaf species. The survey included the most closely related plant species Phragmites australis, common reed, which is sympatric with A. donax in riparian habitats, and also specimens of Zizania texana, Texas wild rice, a Federally listed endangered aquatic grass species in Central Texas. The field (realised) host range of T. romana and R. donacis confirms the predicted host range of these species from quarantine host range testing.

Ex situ phenology of Zizania texana, an endangered aquatic macrophyte, under different water velocities

Texas wild rice (Zizania texana Hitchc.; TWR) is an endangered aquatic macrophyte limited to a 5 km stretch in the upper reach of the San Marcos River in Texas, USA. This study examined the phenology of TWR under different water velocities ex situ over 24 months. The results indicate that TWR exhibits fast initial growth rates of 0.4 m d−1 in total leaf length at 14 weeks in water velocities of 0.4 m s−1. The macrophyte exhibits a plastic reproduction system utilizing both sexual and asexual propagules. Differential development of the pistillate and staminate spikelets prevent self-fertilization and enhances genetic diversity. Plants in slower water velocities produced greater number of flowers and tillers compared to higher water velocities. Seed production was variable among flows but greater in lower water velocities. No difference was detected for seed germination among water velocities which averaged > 57% at 30 days and > 80% at 60 days. The high amount of seeds and tillers produced per plants indicate TWR exhibits reproductive plasticity possibly due to evolving under extreme floods and droughts. At 24 months, TWR allocated greater amounts of biomass to its roots compared to shoots regardless of water velocity which may provide further evidence of an evolutionary function to survive extreme flow conditions by establishing a deep root system.

Propagation and production of an endangered aquatic macrophyte: Texas wildrice (Zizania texanaHitchc.)

Texas wildrice ( Zizania texana Hitchc. [Poaceae]), a federally endangered aquatic macrophyte, is propagated from seeds (grains) and tillers at the USFWS’s San Marcos Aquatic Resource Center (SMARC) for supplementing natural populations in the San Marcos River and life history studies at SMARC. I found seeds to be more efficient and cost-effective compared to using tillers because of the amount of space required for maintaining tillers and the time required to collect wild tillers from the San Marcos River. Seed germination was 67% for 44 germination trials and seedling survival was 88% ( n = 9413) from 2012 to 2014. Growth rates based on total leaf length were 3875 cm (1525 in) at a flow of 0.4 m/s (1.3 ft/s) compared with 1069 cm (420 in) at 0.0 m/s. Texas wild seeds grown in a flow of 0.4 m/s (1.3 ft/s) can be planted in the San Marcos River at 10 to 12 wk post-germination. Outplanting of Texas wildrice in the lower San Marcos River resulted in a 4-fold increase in area coverage at 8 mo post-planting compared to initial planting at 0 mo.

Genetic diversity assessment of in situ and ex situ Texas wild rice (Zizania texana) populations, an endangered plant

Texas wild rice (Zizania texana) is an endangered, aquatic perennial plant endemic to the upper section of the San Marcos River, Texas. Ex situ populations of Z. texana are maintained by the U.S. Fish and Wildlife Service in the event of a catastrophe event. We analyzed the genetics of in situ and ex situ populations of Z. texana to address the following questions: (1) are in situ populations adequately represented in ex situ population? (2) Is there genetic diversity among the current in situ population? (3) Has the current in situ genetic diversity increased or decreased from historical estimates in 2007. Results indicated that the overall ex situ populations were lower in genetic (allelic) diversity compared to the in situ population, with some in situ populations not present in the refugia. Overall, heterozygosity was moderate and ranged from HO=0.530 to HO=0.635 in the wild and HO=0.549 to HO=0.727 in the ex situ population. Inbreeding coefficients (FIS) were near zero or negative indicating that inbreeding is not common within the current populations (in situ and ex situ) suggesting that some populations have an excess of heterozygotes (negative FIS). Analysis of current in situ population structure indicated there are three unique genetic clusters in the San Marcos River. Comparison of the in situ population with historical analysis indicates the genetic diversity of the wild population is dynamic both temporally and spatially. The results indicate that Z. texana exhibits a plastic reproductive system utilizing both asexual (vegetative) and sexual (flowering and seed production) reproduction.

Ecohydraulics in applied river restoration: a case study in the San Marcos River, Texas, USA

The Upper San Marcos River is home to Texas wild rice (Zizania texana), an endangered aquatic macrophyte. Introduced aquatic plants Hydrilla verticillata and Hygrophila polysperma now occupy over 45% of the areal distribution. A two-dimensional hydraulic model was integrated with biological response functions for Zizania, Hydrilla, and Hygrophila to predict optimal locations for Zizania currently occupied by Hygrophila or Hydrilla. At these locations, non-native plants were manually removed and Zizania planted over approximately 20–50% of the exposed areas. Fixed grid locations were monitored bi-weekly over the next year to document plant responses. Monitoring showed a high success rate of expanding Zizania areal coverage and reductions in the non-native species distributions in restoration areas. Utilization of hydraulic modeling to direct spatially explicit aquatic plant restoration activities was shown to be an effective approach with a high success rate at identified restoration sites in the San Marcos River.

Texas wildrice (Zizania texana Hitchc.) propagule production and survival in outdoor ponds as influenced by water depth and velocity

Propagule production (seeds or tillers) of Texas wildrice, Zizania texana Hitchc. (Poaceae), grown in ponds can be manipulated by adjusting water levels and flow rates. Water levels

Use of Macrophytes for Egg Deposition by the Endangered Fountain Darter

Use of habitats for egg deposition by the endangered fountain darter Etheostoma fonticola was evaluated through examination of seven probable microhabitat types in the wild (San Marcos River, Texas) and through laboratory trials with six artificial form-equivalent habitats. Eggs were deposited on native vegetation in the wild; significantly more eggs were found on filamentous algae Rhizoclonium sp. than on Illinois pondweed Potamogeton illinoensis, waterthyme Hydrilla verticillata (an exotic macrophyte), or nonvegetated gravel. Eggs were also found on creeping primrose-willow Ludwigia repens, delta arrowhead Sagittaria platyphylla, and endangered Texas wildrice Zizania texana. Within vegetated habitats, more eggs were deposited on plants growing in sand than silt substrate. This probably corresponds to the habitat requirements for the species; the fountain darter is abundant in slower-moving reaches within the river headwaters, and the presence of silt is an indicator of poor or less-preferred habitat. Results of laboratory trials generally corresponded with field results: larger numbers of eggs were deposited on the form-equivalent Rhizoclonium sp. and L. repens. It is likely that the presence of native macrophytes is necessary for successful fountain darter reproduction.

Travel of Pollen in Experimental Raceways in the Endangered Texas Wild Rice (Zizania texana)

Abstract Travel by pollen from Zizania texana (Texas wild rice) was studied in outdoor cement raceways at the San Marcos National Fish Hatchery and Technology Center, San Marcos, Texas. We examined effects of panicle density and distance from a pollen source on abundance of pollen. There were significantly more pollen grains on traps when panicle number was >40 than there were with fewer panicles. More pollen was on traps within 0.75 m of panicles releasing pollen. We examined the timing of release of pollen by Z. texana by collecting pollen at 6-h intervals for four consecutive 24-h periods. Pollen also was collected at 1-h intervals for four 24-h periods. More pollen was trapped 2400–0600 h (nighttime), compared with 0600–2400 h (daytime); peak hourly release of pollen was 0200–0500 h.

EFFECTS OF WATER TEMPERATURE ON GROWTH OF THE FEDERALLY ENDANGERED TEXAS WILD RICE (ZIZANIA TEXANA)

Abstract We examined the effects of water temperature on growth of Zizania texana (Texas wild rice), with a distribution in the wild restricted to the upper 4.9 km of the San Marcos River, Hays County, Texas. Plants were grown in tanks randomly assigned to 1 of 3 water temperature treatments: 15.5 ± 1.5, 22.5 ± 1.5, and 28.5 ± 1.5°C for 10 weeks during fall 2001. Leaf number, leaf length, and number of reproductive culms were recorded weekly for each plant. Biomass was recorded after 10 weeks. The effects of temperature, week, and their interaction were significant for leaf number and leaf length. Greatest mean leaf number occurred at week 10 for plants grown in 15.5°C water (27.5 ± 6.3); week 8 for 22.5°C water (63.2 ± 4.4); and week 9 for 28.5°C water (42.4 ± 5.5). Leaf length decreased in 15.5°C water from 37.6 ± 3.4 to 32.9 ± 3.3 cm, but increased in 22.5°C water from 41.0 ± 0.6 to 62.0 ± 2.6 cm and from 41.8 ± 0.8 to 60.3 ± 2.7 cm in 28.5°C water. Plants grown in 15.5°C water did not produce reproduc...

Capturing genetic diversity of wild populations for ex situ conservation: Texas wild rice (Zizania texana) as a model

Genebanks complement other conser- vation programs because they preserve genetic diversity needed for future breeding and resto- ration. We evaluated efficiency of capturing genetic diversity, using endangered Zizania texana (Texas wild rice) as a model for plants with recalcitrant seeds. This perennial aquatic grass is restricted to 4 km of the San Marcos River in Texas. An early conservation collection included plants from stands throughout the river, based on the assumption stands would be unique geno- types. Using microsatellite markers, we found that genetic diversity was concentrated in five of 15 large, demographically stable stands; 96 stands smaller than 2 m 2 contributed no unique alleles. High heterozygosity and few duplicate genotypes suggested that sexual reproduction occurs more often than presumed. Simulations of stratified sampling of large stands captured all alleles in only 45 individuals, while random sampling along the river captured much less diversity. The early conservation collection captured as much diver- sity as expected from random sampling. Texas wild rice stands resemble a mainland-island metapopulation; our analyses suggest that strati- fied sampling maximizes genetic diversity for this population dynamic. Demographic and genetic information is important for validating the design of efficient ex situ collections and guiding in situ conservation.

Microsatellite primers for Texas wild rice (Zizania texana), and a preliminary test of the impact of cryogenic storage on allele frequency at these loci

Seed collections in gene banks are useful for the preservation of wild germplasm, providing inexpensive insurance for species that survive in conventional cold storage (−18 °C). Seeds that cannot survive these conditions must be pretreated with cryoprotectants and stored at liquid nitrogen temperatures, which presents unique technical and methodological challenges. Implicit in this approach is the assumption that these added manipulations do not change the genetic diversity of the preserved collections. We used polymorphic microsatellite markers for an endangered aquatic grass, Texas wild rice (Zizania texana), to conduct a preliminary evaluation of the effects of cryogenic preservation of mature embryos on genetic diversity. Using several statistical approaches, we show that allele frequencies did not change in collections of seeds that underwent cryopreservation (cryoprotected) compared to those samples that was not exposed to cryopreservation (control). The retention of the allelic diversity at the five loci examined suggests that there were no significant changes in genetic diversity due to treatments and that these protocols may be appropriate for ex situ conservation of genetically diverse wild germplasm.

Water loss and viability inZizania(Poaceae) seeds during short‐term desiccation

How Texas wild rice, Zizania texana, became isolated in the San Marcos River of Central Texas, hundreds of kilometres from other wild rice populations is not known. Zizania seeds are intolerant of short-term desiccation. Seeds desiccated at 14% relative humidity (RH) and 75% RH do not survive after only 5-6 d and 2-3 wk of drying. Water loss is rapid and reaches a maximum at the time of seed death due to drying. And although all Zizania seeds germinate well following a long, cold dormancy period, Z. texana seeds readily germinate in the isothermic water (22°C) of the San Marcos River and Springs without an obligate, cold dormant period. Within 30-60 d of collection, Z. texana seeds germinate in substantial numbers, unlike seeds of Z. palustris, which require a long, cold dormant period. The Texas population of Z. texana may represent a relict population of a once more widely dispersed wild rice population, since the San Marcos springs probably have never gone dry.

Habitat characterization of Texas wild‐rice (Zizania texana Hitchcock), an endangered aquatic macrophyte from the San Marcos River, TX, USA

1. The habitat of Texas wild-rice (Zizania texana Hitchcock), known only from the spring-fed upper San Marcos River in Central Texas, was classified in terms of physical and chemical conditions, depth, current velocity, associated aquatic macrophytes, and substrate composition. 2. Randomly selected transects in sites with and without Texas wild-rice were evaluated during May, August and January 1994–1995. Physical and chemical conditions (temperature, dissolved oxygen, specific conductance, pH) were found to be nearly constant and uniform both among transect types and sampling dates. Chemical analysis of the substrate likewise showed few differences among transect types. Turbidity was found to be significantly different among transect types on only one sampling date (Kα0.05=0.60; p=0.009), but even non-significant levels of turbidity may present biologically significant impacts to wild-rice plants. 3. Differences in substrate particle size were highly significant (Kα0.05=0.71; p=0.001) with Texas wild-rice occupying sites having moderately coarse to coarse sandy soils (73%) compared with the moderately fine to fine clay soils found at non-rice sites (82%). However, no significant differences were found in organic matter content among rice and non-rice transects (=2.09 and 2.56%, respectively). 4. Texas wild-rice was found primarily in shallow areas of the river (<1 m) and at higher current velocities than those of non-rice sites (≥0.46 m s−1 and ≤0.22 m s−1, respectively). 5. Texas wild-rice appears to be more commonly associated with other native species rather than exotic species. Mean percentage composition of exotic macrophytes did not exceed 29% in areas where Texas wild-rice grew, but they accounted for nearly 47% of the composition in areas where rice did not grow. 6. The results of this study will allow for reliable and accurate identification of the remaining suitable habitat of Texas wild-rice in the San Marcos River for possible reintroduction and development of management plans. Copyright © 1999 John Wiley & Sons, Ltd.

Habitat characterization of Texas wild-rice (Zizania texana Hitchcock), an endangered aquatic macrophyte from the San Marcos River, TX, USA

1. The habitat of Texas wild-rice (Zizaniatexana Hitchcock), known only from the spring-fed upper San Marcos River in Central Texas, was classified in terms of physical and chemical conditions, depth, current velocity, associated aquatic macrophytes, and substrate composition. 2. Randomly selected transects in sites with and without Texas wild-rice were evaluated during May, August and January 1994–1995. Physical and chemical conditions (temperature, dissolved oxygen, specific conductance, pH) were found to be nearly constant and uniform both among transect types and sampling dates. Chemical analysis of the substrate likewise showed few differences among transect types. Turbidity was found to be significantly different among transect types on only one sampling date (Kα0.05=0.60; p=0.009), but even non-significant levels of turbidity may present biologically significant impacts to wild-rice plants. 3. Differences in substrate particle size were highly significant (Kα0.05=0.71; p=0.001) with Texas wild-rice occupying sites having moderately coarse to coarse sandy soils (73%) compared with the moderately fine to fine clay soils found at non-rice sites (82%). However, no significant differences were found in organic matter content among rice and non-rice transects (=2.09 and 2.56%, respectively). 4. Texas wild-rice was found primarily in shallow areas of the river (<1 m) and at higher current velocities than those of non-rice sites (≥0.46 m s−1 and ≤0.22 m s−1, respectively). 5. Texas wild-rice appears to be more commonly associated with other native species rather than exotic species. Mean percentage composition of exotic macrophytes did not exceed 29% in areas where Texas wild-rice grew, but they accounted for nearly 47% of the composition in areas where rice did not grow. 6. The results of this study will allow for reliable and accurate identification of the remaining suitable habitat of Texas wild-rice in the San Marcos River for possible reintroduction and development of management plans. Copyright © 1999 John Wiley & Sons, Ltd.

Effects of current velocity and substrate composition on growth of Texas wildrice ( Zizania texana)

Zizania texana Hitchc., an endangered macrophyte has declined in number during the past 50 years. To determine the effects of substrate composition and current velocity on plant growth, plants were grown in pots containing either fine or coarse sediment at three sites in Spring Lake, Hays Co., TX. Each site was similar in depth but differed in current velocity. Plants were allowed to grow for 6 weeks and then harvested. Growth was greater on fine sediments. There was significant interaction between flow and sediment with respect to aboveground biomass and stem density and, there was significant flow effect on leaf length and stem density. Stem density was greater in fast flowing water (0.40–0.49 m s −1) than either moderate (0.12–0.24 m s −1) or slow flowing (0.05–0.12 m s −1) water. The decline in Zizania texana population can be attributed, in part, to physical changes to Zizania texana habitat.