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''Thymophylla tephroleuca'' (formerly ''Dyssodia tephroleuca'') is a rare species of flowering plant known by the common names ashy dogweed and ashy pricklyleaf. It is endemic to Texas in the United States, where it occurs in two counties near the Mexican border. It became rare due to the destruction and degradation of its habitat.〔(''Thymophylla tephroleuca''. ) The Nature Conservancy.〕〔(''Thymophylla tephroleuca''. ) Center for Plant Conservation.〕 It is a federally listed endangered species of the United States. This plant, a shrub or subshrub, produces a clump of stems up to 30 centimeters tall. The herbage is ashy gray-green, gray, or whitish due to a layer of white woolly hairs. The leaves are linear to threadlike and are arranged alternately along the stems. They measure 1 to 1.5 centimeters long. The inflorescence is a flower head with a bell-shaped involucre of woolly-haired phyllaries. There are 12 or 13 yellow ray florets and about 30 disc florets at the center. The fruit is an achene with a pappus of scales.〔(''Thymophylla tephroleuca''. ) Flora of North America.〕 Blooming occurs mostly in March through May but it may bloom at other times depending on rainfall.〔 This plant is likely a relict, a rare species remaining in a grassland habitat type that was once more common.〔USFWS. (Final rule to determine ''Dyssodia tephroleuca'' (Ashy dogweed) to be an endangered species. ) ''Federal Register'' July 19, 1984.〕 Most of the local territory has converted to brushland dominated by cenizo (''Leucophyllum frutescens'') blackbrush (''Coleogyne ramosissima''), and creosote bush (''Larrea tridentata''). Other dominant plant species include mesquite (''Prosopis glandulosa''), goatbush (''Castela texana''), anacahuita (''Cordia boissieri''), and javelina brush (''Microrhamnus ericoides''). The introduced buffelgrass (''Cenchrus ciliaris'') is common.〔USFWS. (''Thymophylla tephroleuca'' Recovery Plan. ) July 29, 1988.〕 By 1979 this plant was known from a in Zapata County, Texas. By the time the plant was placed on the Endangered Species List in 1984 there was a single population containing about 1300 plants.〔 This population is bisected by a highway.〔 More populations have been found in the years since and currently there are six in Zapata and Webb Counties.〔 Threats to the species have included highway maintenance, because the plant grows directly next to a highway. Dying plants have been observed at the highway's edge, a possible sign of herbicide application. The installation of a gas pipeline likely destroyed some plants and its maintenance is a threat to others in the area. Grazing is not a direct threat because cattle do not eat the foul-smelling plant, but their trampling may compact the soil. The introduction of buffelgrass for better grazing has led to drastic changes in the plant community, because it spreads and competes easily with other species.〔 ==References== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Thymophylla tephroleuca」の詳細全文を読む スポンサード リンク
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