Centaurea solstitialis

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Centaurea solstitialis is a serious weed pest, especially in the western United States, where it has invaded millions of acres of rangelands, and it is listed as a noxious weed in eleven western states and two Canadian provinces. It is a strong competitor in infested areas, often forming dense colonies. It is very difficult to control or eradicate once it becomes established. In addition, yellow star-thistle is poisonous to horses; when ingested over a prolonged period it causes a neurological disorder called equine nigropallidal encephalomalacia, or “chewing disease.” Although its bitter taste and spiny heads usually deter grazing animals, horses sometimes will seek it out. Yellow star-thistle tends to spread in rangelands when more palatable plants are consumed.

appendage colorationstramineous + and brown +
appendage external texturescarious +
appendage shapeobtuse +, abruptly spine + and tipped +
array architectureopen + and leafy +
blade shapelinear +, oblong + and entire +
body colorationgreen +
body shapeovate +
bristle colorationwhite +
bristle countmany +
bristle sizeunequal +
chromosome count16 +
corolla colorationyellow +
corolla variabilityequal +
cypsela colorationbrown +, inner + and mottled +
cypsela external textureglabrous +
cypsela habitdimorphic +
cypsela positionouter +
floret countmany +
floret prominenceinconspicuous +
floret sizeslender +
flowering timesummerjun +, jul +, aug +, sep +, oct +, year round +, summer +, spring +, winter +, fall +, nov +, apr +, dec +, jan +, jun +, may +, feb + and mar +
habitatroadsides +, fields +, pastures + and woodlands +
head architecturelong-pedunculate +
head architecture or shapedisciform +
head arrangementsingly + and in open leafy arrays +
involucre external texturecobwebby-tomentose + and glabrous +
involucre shapeovoid +
leaf architecturepetiolate + and tapered to base +
leaf countabsent +
leaf external texturegray-tomentose +, scabrous + and short-bristly +
leaf other or positionproximal cauline +
leaf positionbasal +
margin positioncauline +
margin shapelobed +, dissected + and long-decurrent +
pappus widthfine +
spine fragilitystout +
stem architecturesimple + and branched +
stem external texturegray-tomentose +
whole organism habitbushy +
whole organism life styleannual + and plant +
whole organism shaperounded +