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Taeniatherum caput-medusae
''Taeniatherum caput-medusae'' is a species of grass known by the common name medusahead. 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.〕 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 lower 48 of the 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 outcompetes native vegetation, reduces land value, and creates a wildfire hazard.
==History and origin==
Medusahead was first described in the United States in Oregon in 1903 as ''Elymus caput-medusae'' by Thomas Howell. 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.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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