Centaurea solstitialis
Centaurea iberica
Barnaby star-thistle, centauré du solstice, golden starthistle, St. Barnaby's thistle, yellow cockspur, yellow knapweed, yellow star-thistle
Iberian knapweed, Iberian star thistle or knapweed, Iberian star-thistle
simple or often branched from base, forming rounded bushy plants, gray-tomentose.
1–several, divaricately much branched, often forming rounded mound, puberulent to loosely 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.
hispidulous to loosely tomentose, ± glabrate, minutely resin-gland-dotted;
proximal leaves petiolate, blades 10–20 cm, margins 1–2 times pinnately lobed or dissected, rosette with central cluster of spines;
mid sessile, not decurrent, blades ± lanceolate, shorter;
distal blades linear to oblong, entire to coarsely dentate or shallowly lobed.
ovoid, 13–17 mm, loosely cobwebby-tomentose or becoming glabrous.
ovoid to hemispheric, (10–)13–18 mm.
many;
corollas yellow, all ± equal, 13–20 mm;
sterile florets slender, inconspicuous.
many;
corollas white, pink, or pale purple, those of sterile florets slender, 15–20 mm, those of fertile florets 15–20 mm.
appendages scarious, obtuse or abruptly spine tipped.
appendages truncate, spineless.
disciform, borne singly or in open leafy arrays, long-pedunculate.
disciform, borne singly or in leafy cymiform arrays, sessile or short-pedunculate.
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.
white- or brown-streaked, 3–4 mm, glabrous;
pappi of white bristles 1–2.5(–3) mm.
phyllaries: bodies pale green, ovate, appendages stramineous to brown, each with palmately radiating cluster of spines, and stout central spine 10–25 mm.
phyllaries: bodies greenish or stramineous, ovate, scarious–margined, appendages stramineous, spiny–fringed at base, each tipped by stout spreading spine (0.5–)1–3 cm.
= 16.
= 16, 20.
Centaurea solstitialis
Centaurea iberica
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.)
Centaurea iberica is native to southeastern Europe through central Asia.
Iberian star thistle is considered to be a noxious weed in several states of the western United States. Weed control measures in Oregon and Washington have apparently eradicated the species in those states. Centaurea iberica is very similar to C. calcitrapa, from which it differs by its pappose cypselae and often more robust habit. The Kansas and Wyoming plants were originally reported as C. calcitrapa (R. L. McGregor 1986).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
- Local floras:
BC, 
CA, 
OR, 
WA - Local Web sites: CalFlora, CalPhotos,
Flora NW, 
Go Botany, 
IL Wildflowers, 
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MD Biodiversity, 
MI Flora, 
MN Wildflowers, 
MO Plants, 
PNW Herbaria, Turner Photog. 
WildflowerSearch
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USDA Plants Database- LBJ Wildflower Center
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