Centaurea calcitrapa |
Centaurea diluta |
|
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caltrops, centaurée chausse-trappe, chausse-trappe, purple knapweed, purple star-thistle, red star-thistle |
North African knapweed, star-thistle |
|
Habit | Annuals, biennials, or short-lived perennials, 20–100 cm. | Annuals or perennials, to 200 cm. |
Stems | 1–several, often forming rounded mounds, puberulent to loosely tomentose. |
simple proximally, openly branched distally, glabrous or thinly hairy. |
Leaves | puberulent to loosely gray-tomentose, becoming ± glabrous, minutely resin-gland-dotted; proximal leaves petiolate, blades 10–20 cm, 1–3 times pinnately dissected, rosette with central cluster of spines; mid sessile, not decurrent, blades ovate, usually less than 10 cm, narrowly lobed; distal blades linear to oblong, entire to shallowly lobed. |
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, 15–20 × 6–8 mm. |
ovoid, 8–15 mm diam. |
Florets | 25–40; corollas purple, all ± equal, 15–24 mm; sterile corollas slender. |
many; corollas pink-purple, those of sterile florets 25–30 mm, enlarged, raylike, those of fertile florets ± 20 mm. |
Inner phyllaries | appendages truncate, spineless. |
|
Heads | disciform, borne singly or in leafy cymiform arrays, sessile or short-pedunculate. |
radiant, in open cymiform arrays, pedunculate. |
Cypselae | white or brown-streaked, 2.5–3.4 mm, glabrous; pappi 0. |
tan, 3–3.5 mm; pappi many, white, unequal bristles 3–5 mm. |
Principal | phyllaries: bodies greenish or stramineous, ovate, scarious-margined, appendages stramineous, spiny fringed at base, each tipped by a stout spreading 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 | = 20. |
= 20. |
Centaurea calcitrapa |
Centaurea diluta |
|
Phenology | Flowering summer–autumn (Jun–Nov). | Flowering spring (Apr–Jun). |
Habitat | Pastures, fields, roadsides | Escaped from cultivation in disturbed sites |
Elevation | 0–1700 m (0–5600 ft) | 0–100 m (0–300 ft) |
Distribution |
AL; AZ; CA; DC; FL; GA; IA; IL; MA; MD; NJ; NM; NY; OR; PA; UT; VA; WA; ON; Europe; Africa
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CA; MO; NY; sw Europe; n Africa [Introduced in North America] |
Discussion | Centaurea calcitrapa is native to southern Europe and northern Africa. It is listed as a noxious weed in Arizona, California, Nevada, New Mexico, Oregon, and Washington. These plants are unpalatable and increase on rangelands as more desirable forage plants are consumed. Dense stands are impenetrable because of the vicious spines on the mature involucres. Centaurea ×pouzinii de Candolle, an apparently stabilized hybrid between Centaurea aspera (2n = 22) and C. calcitrapa (2n = 20), has been reported from California. A chromosome count of 2n = 42 has been reported from California material of this nothospecies (A. M. Powell et al. 1974). Centaurea ×pouzinii can be distinguished from C. calcitrapa by its shorter spines and by cypselae with a short pappus. Reports of C. calcitrapoides Linnaeus from North America are apparently based on this hybrid. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
|
Source | FNA vol. 19, p. 191. | 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) |
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