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:''For the race horse, see Australasian Oaks or Storm Queen Stakes.'' :''"Basket flower" and spelling variants redirect here. In Australia, this usually means the unrelated plant ''Adenanthos obovatus. ''Centaurea'' ()〔''Sunset Western Garden Book,'' 1995:606–607〕 is a genus of between 350 and 600 species of herbaceous thistle-like flowering plants in the family Asteraceae. Members of the genus are found only north of the equator, mostly in the Eastern Hemisphere; the Middle East and surrounding regions are particularly species-rich. Common names for this genus are centaury, centory, starthistles, knapweeds, centaureas and the more ambiguous "bluets"; a vernacular name used for these plants in parts of England is "loggerheads" (Common Knapweed). The ''Plectocephalus'' group – possibly a distinct genus – is known as basketflowers. "Cornflowers" is used for a few species, but that term more often specifically means ''C. cyanus'' (sometimes also called "Basket Flower"). The common name "centaury" is sometimes used, although this also refers to the unrelated plant genus ''Centaurium''.〔Keil (2006), Keil & Ochsmann (2006)〕 ==Description and ecology== Knapweeds are robust weedy plants. Their leaves, spiny in some species, are usually deeply divided into elongated lobes at least in the plants' lower part, becoming entire towards the top. The "flowers" (actually pseudanthium inflorescences) are diverse in colour, ranging from intense blues, reds and yellows to any mixture of these and lighter shades towards white. Often, the disk flowers are much darker or lighter than the ray flowers, which also differ in morphology and are sterile. Each pseudanthium sits atop a cup- or basket-like cluster of scaly bracts, hence the name "basketflowers". Many species, in particular those inhabiting more arid regions, have a long and strong taproot. Certain knapweeds have a tendency to dominate large stretches of landscape together with a few other plants, typically one or two grasses and as many other large herbs. The Common Knapweed (''C. nigra'') for example is plentiful in the mesotrophic grasslands of England and nearby regions. It is most prominently found in pastures or meadows dominated by Cock's-foot (''Dactylis glomerata'') as well as either of Crested Dog's-tail (''Cynosurus cristatus'') and False Oat-grass (''Arrhenatherum elatius''). It is also often found in mesotrophic grassland on rendzinas and similar calcareous soils in association with Glaucous Sedge (''Carex flacca''), Sheep's Fescue (''Festuca ovina''), and either Tor-grass (''Brachypodium pinnatum'') and Rough Hawkbit (''Leontodon hispidus''), or Upright Brome (''Bromus erectus''). In these grasslands, Greater Knapweed (''C. scabiosa'') is found much more rarely by comparison, often in association with Red Festuce (''F. rubra'') in addition to Cock's-foot, False Oat-grass. Due to their habit of dominating ecosystems under good conditions, many ''Centaurea'' species can become invasive weeds in regions where they are not native. In parts of North America, Diffuse Knapweed (''C. diffusa''), Spotted Knapweed (''C. maculosa'') and Yellow Starthistle (''C. solstitialis'') cause severe problems in agriculture due to their uncontrolled spread. The seeds are typically transported by human traffic, in particular the tires of all-terrain vehicles. The two knapweeds are harmful mainly because they are strongly allelopathic, producing powerful toxins in their roots that stunt the growth of plants around them not adapted to this.〔Hierro & Callaway (2003), Vivanco ''et al.'' (2004)〕 Yellow Starthistle, meanwhile, is inedible to most livestock due to its spines and apparently outright poisonous to horses and other equines. However, efficient methods of biological control by insect pests of these weeds have been developed; the knapweeds can also exploited to their detriment by targeted grazing. Controlled burning may also be used, though the timing is important to avoid the plants having seeded already, and neither allowing sufficient time for them to regrow from the rootstock.〔Emery & Gross (2005)〕 Yet other species of ''Centaurea'' – mostly ones that occur between Italy and the Caucasus – are endemics of a single island or valley, and some of these are endangered. The Akamas Centaurea (''Centaurea akamantis'') of Cyprus is almost extinct, while the western Caucasus endemics ''C. leptophylla'' and ''C. straminicephala'' are at least very rare and ''C. hedgei'' and ''C. pecho'' from the same region are certainly not abundant either. The last four species would be adversely affected by the proposed Yusufeli Dam, which might actually destroy enough habitat to push the two rarer ones over the brink of extinction. ''Centaurea'' are copious nectar producers, especially on high-lime soils. The high nectar yield of the genus makes it very attractive to insects such as butterflies – including the endangered Karner Blue (''Lycaeides melissa samuelis'') which visits introduced Spotted Knapweed – and day-flying moths – typically Zygaenidae, such as ''Zygaena loti'' or the Six-spot Burnet (''Z. filipendulae''). The larvae of some other Lepidoptera species use ''Centaurea'' species as food plants; see List of Lepidoptera that feed on Centaurea. Several of these are used in biological control of invasive knapweeds and starthistles. Larvae of several true weevils (Curculionidae) of the subfamily Lixinae also feed on ''Centaurea''. Some genera – such as ''Larinus'' whose larval food is flowerheads – have many species especially adapted to particular knapweeds or starthistle and are used in biological control too. These include the Yellow Starthistle Flower Weevil (''L. curtus'') for Yellow Starthistle, Lesser Knapweed Flower Weevil (''L. minutus'') for Diffuse Knapweed and Blunt Knapweed Flower Weevil (''L. obtusus'') for Spotted Knapweed. Broad-nosed Seedhead Weevil (''Bangasternus fausti'') larvae eat Diffuse, Spotted and Squarrose Knapweed (''C. virgata'' ssp. ''squarrosa''), while those of the Yellow Starthistle Bud Weevil (''B. orientalis'') do not seem to live on anything other than Yellow Starthistle and occasionally Purple Starthistle (''C. calcitrapa''). But perhaps most efficient in destroying developing Yellow Starthistle seedheads is the larva of the Yellow Starthistle Hairy Weevil (''Eustenopus villosus''). Knapweed Root Weevil (''Cyphocleonus achates'') larvae bore into the roots of Spotted and to a lesser extentely Diffuse Knapweed, sometimes killing off the entire plant. Also used in biological control are Tephritidae (peacock flies) whose larvae feed on ''Centaurea''. Knapweed Peacock Fly (''Chaetorellia acrolophi'') larvae eat Spotted Knapweed and some other species. The Yellow Starthistle Peacock Fly (''C. australis'') has an initial generation each year which often uses Cornflower (''C. cyanus'') as larval food; later generations switch to Yellow Starthistle. The flies are generally considered less efficient in destroying the growing seedheads than the weevils, but may be superior under certain conditions; employing flies and weevils in combination is expensive and does not noticeably increase their effect. 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「Centaurea」の詳細全文を読む スポンサード リンク
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