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golden starthistle, St. Barnaby's thistle, yellow cockspur, yellow knapweed, yellow star-thistle

Habit Annuals, 10–100 cm.

simple or often branched from base, forming rounded bushy plants, gray-tomentose.


gray-tomentose and scabrous to short-bristly;

basal and proximal cauline petiolate or tapered to base, usually absent at anthesis, blades 5–15 cm, margins pinnately lobed or dissected;

cauline long-decurrent, blades linear to oblong, 1–10 cm, entire.


disciform, borne singly or in open leafy arrays, long-pedunculate.


ovoid, 13–17 mm, loosely cobwebby-tomentose or becoming glabrous.



corollas yellow, all ± equal, 13–20 mm;

sterile florets slender, inconspicuous.

Inner phyllaries

appendages scarious, obtuse or abruptly spine tipped.


dimorphic, 2–3 mm, glabrous, outer dark brown, without pappi, inner white or light brown, mottled;

pappi of many white, unequal bristles 2–4 mm, fine.


phyllaries: bodies pale green, ovate, appendages stramineous to brown, each with palmately radiating cluster of spines, and stout central spine 10–25 mm.


= 16.

Centaurea solstitialis

Phenology Flowering mostly summer–autumn (Jun–Oct), sometimes year-round in frostfree coastal habitats.
Habitat Roadsides, fields, pastures, woodlands
Elevation 0–2000 m [0–6600 ft]

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.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

from FNA
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Parent taxa Asteraceae > tribe Cardueae > Centaurea
Sibling taxa
C. benedicta, C. calcitrapa, C. cyanus, C. depressa, C. diffusa, C. diluta, C. iberica, C. jacea, C. macrocephala, C. melitensis, C. montana, C. nigra, C. nigrescens, C. phrygia, C. scabiosa, C. stoebe, C. sulphurea, C. virgata, C. ×moncktonii
Name authority Linnaeus: Sp. Pl. 2: 917. (1753)
Source Flora of North America vol. 19, p. 193.
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