|
''Helenium virginicum'' is a rare species of flowering plant in the aster family known by the common name Virginia sneezeweed. It occurs in the United States, where it has a disjunct distribution; it is known only from Virginia and Missouri.〔(Biota of North America Program 2014 county distribution map )〕 It is limited to a specific type of habitat and it is threatened by modification of this habitat.〔USFWS. (Determination of threatened status for Virginia Sneezweed (''Helenium virginicum''), a plant from the Shenandoah Valley of Virginia. ) ''Federal Register'' November 3, 1998.〕〔Knox, J. S., F. W. Stearns and C. K. Dietzel. (1999). Factors controlling the distribution and abundance of the narrow endemic, ''Helenium virginicum'' (Asteracea): antiherbivore defense. Banisteria 13:95-100.〕 It was federally listed as a threatened species of the United States in 1998.〔 At the time the plant received federal protection it was known from 28 populations in two Virginia counties.〔 Soon after, a population of similar plants was found in Missouri and by genetic analysis were confirmed to be of the same species.〔(''Helenium virginicum''. ) The Nature Conservancy.〕〔(Biologists to determine if rare plant deserves protection. ) ''Innovations Report'' September 23, 2009.〕 Searches turned up a total of 44 occurrences in six counties in the Ozark Highlands of Missouri.〔 This disjunct distribution was probably caused by the cleaving of the species' geographical range during Pleistocene glaciation, leaving two relict ranges.〔(''Helenium virginicum''. ) Flora of North America.〕 ''Helenium virginicum''is similar to and often mistaken for ''Helenium autumnale'', the common sneezeweed.〔 It is a perennial herb generally growing to a maximum height between 70 centimeters and 1.1 meters (28-44 inches), but it is known to reach 1.7 meters (68 inches or 5 2/3 feet) at times.〔 There is a basal rosette of leaves and an erect, winged stem lined with lance-shaped leaves that become smaller toward the top of the stem. The inflorescence has several flower heads, each with a spherical disc covered with disc florets and lined with yellow ray florets just over a centimeter (0.4 inches) long.〔〔 Blooming occurs in July through October.〔 The plant is self-incompatible.〔Messmore, N. A. and J. S. Knox. (1997). (The breeding system of the narrow endemic, ''Helenium virginicum'' (Asteraceae). ) ''Journal of the Torrey Botanical Society'' 124:4 318-21.〕 ''Helenium virginicum'' only grows near sinkhole ponds in the Ozark Highlands of Missouri and the western margin of the Blue Ridge Mountains in Virginia.〔〔Rimer, R. L. and J. W. Summers. (2006). (Range and ecology of ''Helenium virginicum'' in the Missouri Ozarks. ) ''Southeastern Naturalist'' 5:3 515.〕 These ponds are lined with clay or bedrock and are filled with water from about January to June or July each year. They may take the form of actual holes or they may be more like very wet meadows. The ponds are often actively grazed by cattle and can tolerate disturbance.〔 The hydrology of the sinkholes varies seasonally and year to year, causing a similar fluctuation in the population and recruitment of the sneezeweed.〔(''Helenium virginicum''. ) Center for Plant Conservation.〕 The greatest threat to this species is habitat modification.〔〔 Destruction of the sinkhole habitat could lead to the extinction of the 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「Helenium virginicum」の詳細全文を読む スポンサード リンク
|
