Centaurea solstitialis |
Centaurea diluta |
|
---|---|---|
Barnaby star-thistle, centauré du solstice, golden starthistle, St. Barnaby's thistle, yellow cockspur, yellow knapweed, yellow star-thistle |
North African knapweed, star-thistle |
|
Habit | Annuals, 10–100 cm. | Annuals or perennials, to 200 cm. |
Stems | simple or often branched from base, forming rounded bushy plants, gray-tomentose. |
simple proximally, openly branched distally, glabrous or thinly hairy. |
Leaves | 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. |
thinly pubescent, basal and proximal cauline petiolate, blades 10–15 cm, margins coarsely pinnately lobed; mid cauline sessile or short-petiolate, short-decurrent, blades obovate or narrowly oblong, 2–8 cm, entire to pinnately lobed; distal cauline oblong, entire to irregularly lobed. |
Involucres | ovoid, 13–17 mm, loosely cobwebby-tomentose or becoming glabrous. |
ovoid, 8–15 mm diam. |
Florets | many; corollas yellow, all ± equal, 13–20 mm; sterile florets slender, inconspicuous. |
many; corollas pink-purple, those of sterile florets 25–30 mm, enlarged, raylike, those of fertile florets ± 20 mm. |
Inner phyllaries | appendages scarious, obtuse or abruptly spine tipped. |
|
Heads | disciform, borne singly or in open leafy arrays, long-pedunculate. |
radiant, in open cymiform arrays, pedunculate. |
Cypselae | 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. |
tan, 3–3.5 mm; pappi many, white, unequal bristles 3–5 mm. |
Principal | 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, ovate, scarious-margined, appendages stramineous to brown, scarious, fringed with slender teeth, tipped by slender spines 1–5 mm. |
Innermost | phyllaries unarmed with brown, expanded, lacerate appendages. |
|
2n | = 16. |
= 20. |
Centaurea solstitialis |
Centaurea diluta |
|
Phenology | Flowering mostly summer–autumn (Jun–Oct), sometimes year-round in frostfree coastal habitats. | Flowering spring (Apr–Jun). |
Habitat | Roadsides, fields, pastures, woodlands | Escaped from cultivation in disturbed sites |
Elevation | 0–2000 m (0–6600 ft) | 0–100 m (0–300 ft) |
Distribution |
AZ; CA; CO; CT; DE; FL; IA; ID; IL; IN; KS; KY; MA; MD; MI; MN; MO; MT; NC; ND; NE; NH; NJ; NM; NV; NY; OH; OK; OR; PA; RI; SC; SD; TN; TX; UT; VA; WA; WI; WV; WY; AB; MB; ON; SK; s Europe [Widely introduced]
|
CA; MO; NY; sw Europe; n Africa [Introduced in North America] |
Discussion | 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.) |
|
Source | FNA vol. 19, p. 193. | FNA vol. 19, p. 192. |
Parent taxa | Asteraceae > tribe Cardueae > Centaurea | Asteraceae > tribe Cardueae > Centaurea |
Sibling taxa | ||
Name authority | Linnaeus: Sp. Pl. 2: 917. (1753) | Aiton: Hort. Kew. 3: 261. (1789) |
Web links |
|