Taeniatherum is a genus of Eurasian and North African plants in the grass family.Nevski, Sergei Arsenjevic. 1934. Trudy Sredne-Aziatskogo Gosudarstvennogo Universiteta. Seriya 8b, Botanika 17: 38Grassbase – The World Online Grass FloraFrederiksen, S. 1986. Revision of Taeniatherum (Poaceae). Nordic Journal of Botany 6(4): 389–397
The only recognized species is medusahead (Taeniatherum caput-medusae) which is native to southern and central Europe (from Portugal to European Russia), North Africa (Algeria, Morocco, Tunisia), and Asia (from Turkey and Saudi Arabia to Pakistan and Kazakhstan).Kew World Checklist of Selected Plant FamiliesAltervista Flora Italiana genere TaeniatherumDanin, A. (2004). Distribution Atlas of Plants in the Flora Palaestina area: 1–517. The Israel Academy of Sciences and Humanities, JerusalemCope, T.A., Knees, S.G. & Miller, A.G. (2007). Flora of the Arabian peninsula and Socotra 5(1): 1–387. Edinburgh University PressDobignard, D. & Chatelain, C. (2010). Index synonymique de la flore d'Afrique du nord 1: 1–455. Éditions des conservatoire et jardin botaniques, Genève It is also naturalized in southern Australia, Chile, and parts of North America.Biota of North America 2013 county distribution mapAusgrass2, Grasses of Australia, Taeniatherum caput-medusaeZuloaga, F.O., Morrone, O., Belgrano, M.J., Marticorena, C. & Marchesi, E. (eds.) (2008). Catálogo de las Plantas Vasculares del Cono Sur. Monographs in Systematic Botany from the Missouri Botanical Garden 107: 1–3348
This aggressive winter annual grass is changing the ecology of western rangelands in North America.Zimmerman, J.R., et al. Medusahead: Economic Impact and Control in Nevada. University of Nevada-Reno Fact Sheet FS-02-37. It was first observed in the United States in Oregon in 1903 by Thomas Howell. Forty-eight percent of the total land area of the United States is rangeland, pastureland, national parks, nature preserves, and other wildlands. These lands are essential for agriculture and for protecting the integrity of ecological systems. Natural areas contain many nonnative plant species that occur as self-sustaining populations in the continental United States, including medusahead. As of 2005, medusahead infested approximately in the 17 western states (from North Dakota south to Texas and west to the Pacific coast), and spreads at an average rate of 12% per year.Duncan, C.A., et al. (2004). Assessing the economic, environmental, and societal losses from invasive plants on rangeland and wildlands. Weed Technology 18:1411–1416 As medusahead spreads, it can outcompete native vegetation in overgrazed rangelands, reduces land value, and creates a wildfire hazard.Dremann, Craig C. Field Notebook No. 260, page 20, Soil samples from the U.C. Sierra Foothill Research & Extension Center, Browns Valley, CA. June 2016
History and origin Medusahead was first described Elymus caput-medusae by Carl Linnaeus. Nevski recommended in 1934 that the Russian types of medusahead should be classified in a separate genus, Taeniatherum. In the 1960s, it was suggested by Jack Major of the University of California that there are three geographic and morphologically distinct taxa: T. caput-medusae, T. asperum, and T. crinitum. After traveling in Russia, Major thought the proper classification for the plant introduced to North America was Taeniatherum asperum. The genus was revised in 1986 by the Danish scientist Signe Frederiksen. He made the previously mentioned distinct taxa into subspecies of Taeniatherum caput-medusae.Kostivkovsky, V. and J. A. Young. (2000). Invasive exotic rangeland weeds: A glimpse at some of their native habitats. Rangelands 22:6 3–6.
The subspecies caput-medusae is a native species to Europe, and is mostly restricted to Spain, Portugal, southern France, Algeria, and Morocco. Subspecies crinitum is found from Greece and the Balkans east into Asia, and the range of subspecies asperum completely overlaps the other two subspecies.
In Asia, medusahead is widespread in Turkmenistan, Iran, Syria, and in the northern portion of Israel, inhabiting low mountains and plateau areas. It is both an agronomic and rangeland weed. It prefers soils rich in nitrogen, and is often found on stony or gravelly soils. Carbonized seeds of this weed have been found in early agricultural archaeological sites in Iran. Seeds were first found in strata corresponding to the early days of sheep and goat husbandry.
Life cycle and growing habits Medusahead is a winter annual, germinating in the fall and undergoing root growth in the winter and early spring. Since its roots develop early and reach deep in the soil, it outcompetes native plants for moisture. It flowers in early spring, and by June or July its seeds, which are covered with tiny barbs, are mature. The barbs help the seeds attach to livestock, humans or vehicles that pass by. As the grass grows it accumulates silica, making it unpalatable to livestock except for early in its life cycle. It creates a dense layer of litter, and because of the silica content, the litter decomposes more slowly than that of other plants. This litter suppresses native plant growth while encouraging the germination of its own seed, and after a few years it creates an enormous load of dry fuel that can lead to wildfires.
Stands of medusahead vary in density from several hundred to 2,000 plants per square foot. This variance is directly related to annual precipitation, soil type, and other vegetation in the area. Research has suggested that medusahead is highly adaptable and can produce more seeds at a density of one plant per square foot than 1,000 plants per square foot. Since it matures later than most other annuals, it is easy to identify as it is often bright green when the other annuals are brown. As it matures, it turns shades of purple and eventually tan. This unique phenological signature can be utilized in the management of this invasive species. A recently developed method of assessing greenness in aerial color infrared (CIR) imagery using Normalized Difference Vegetation Index (NDVI) values to differentiate between medusahead and other more desirable species may help land managers determine where control methods are necessary.Malmstrom, C.M., H.S. Butterfield, L. Planck, C.W. Long, and V.T. Eviner. (2017). Novel fine-scale aerial mapping approach quantifies grassland weed cover dynamics and response to management. PLOS ONE 12(10): e0181665.
Medusahead seeds disperse relatively short distances and dispersal decreases as distance from the plant increases. Seeds are very well adapted for dispersal by adhesion to moving objects. The relatively long period of medusahead seed dispersal from July to October may be an adaptation to increase the likelihood of adhesion to animals.Davies, K. W. (2008). Medusahead dispersal and establishment in sagebrush steppe plant communities. Rangeland Ecology and Management 61: 110–115.
Identification Medusahead ranges in height from 20 to 60 centimeters.Jepson Manual Treatment It has slender, weak stems that often branch at the base. It has spike inflorescences similar to those of wheat or rye. The lemmas have long awns and the glumes have shorter ones, giving the seed head a layered look.Stubbendieck, J.L., et al. (2004). North American Wildland Plants: A Field Guide. University of Nebraska Press. As the awns dry, they twist and spread in all directions, similar to the snake-covered head of the mythological Medusa. The barbs on the awns help the seed drive into the soil.US Forest Service Fire Ecology The grainlike seed may remain viable in the soil for a number of years.
Effects on wildlife and grazing The grazing capacity of land infested with medusahead can be reduced by up to 80%.Davies, K.W. and D. D. Johnson. (2008). Managing medusahead in the intermountain west is at a critical threshold. Rangelands. 30:13–15 Wildlife habitat and biodiversity also suffer, and the weed can eventually lead to alterations in ecosystem functions. The impact medusahead can have on species relying on sagebrush is rarely mentioned. It can exacerbate the decline of sage-grouse (genus Centrocercus) as it replaces plant communities that provide critical habitat for the bird.
Other species, such as mule deer and chukar partridges, tend to avoid areas overrun with medusahead because it is not a good food source. In the case of mule deer, a study in Oregon found that even though extensive stands of medusahead were available, those areas (when compared to other plant communities) were least preferred by feeding mule deer in winter, summer, and fall; and they ranked low in the spring. This decrease in feeding was related back to the dominance of medusahead, which deer do not eat, and the subsequent lack of forbs.Bodurtha, T.S., et al. (1989). Mule deer habitat use related to succession in a bunchgrass community. Journal of Wildlife Management 53:2 314–319. Chukar partridges will ingest medusahead seeds (caryopses ) if given no other choice. However, if they are given free access to all the medusahead seeds they will eat, they suffered from a significant loss in body weight. Largely undamaged seeds were found in their droppings, suggesting that the digestibility of medusahead by the birds was low.Savage, D.E., et al. (1969). Utilization of medusahead and downy brome caryopses by Chukar Partridges. The Journal of Wildlife Management 33:4 975–978.
Control methods No single control method will eradicate medusahead. For best results, it is often necessary use a form of integrated pest management that combines two or more of the following methods.
Mechanical Plowing and disking are two methods of mechanical control. Both methods can effectively control medusahead and can reduce infestation by 65% to 95% the next growing season. Eradication of medusahead by mechanical control by itself is nearly impossible, but when followed by chemical control or revegetation chances for eradication increase dramatically.
Burning Fire is often considered a low cost method of improving rangeland condition. It has been given attention in the control of medusahead because many of the areas infested with it are too rocky or steep for other treatments. Control of medusahead with fire had differing results in California. In some areas, more desirable plant communities came back after a fire, while in other areas medusahead continued to dominate after fire. There are a few guidelines that should be followed when burning medusahead. The burn should be conducted when the seed is in the soft dough stage (when the seeds exude a milky substance when squeezed) in the late spring. The initial fire should be one that is slow burning, something that is easily achieved by burning into the wind. This prevents the fire from advancing too rapidly and ensures that the current year's herbage is burned and periods of maximum temperature are long enough to kill medusahead caryopses. Viable medusahead caryopses are found almost entirely in the litter and on the soil surface.Young, J.A., et al. (1972). Influence of repeated annual burning on a medusahead community. Journal of Range Management 25:5 372–375.
Past studies on the effectiveness of burning may have given researchers false hope. The caryopses have severe temperature dependent afterripening requirements which prevent seeds from germinating at temperatures above 10˚C for about 180 days after maturity. If these conditions are met, many medusahead caryopses from the litter and soil in burned plots were viable. Since the seeds did not germinate during the afterripening period, researchers were misled into believing they were accomplishing more by burning than was actually the case.
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