Flora of North America species comparison

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Centaurea calcitrapa

caltrops, centaurée chausse-trappe, chausse-trappe, purple knapweed, purple star-thistle, red star-thistle
Habit Annuals, biennials, or short-lived perennials, 20–100 cm.
Stems

1–several, often forming rounded mounds, puberulent to loosely tomentose.
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.
Involucres

ovoid, 15–20 × 6–8 mm.
Florets

25–40;

corollas purple, all ± equal, 15–24 mm;

sterile corollas slender.
Inner phyllaries

appendages truncate, spineless.
Heads

disciform, borne singly or in leafy cymiform arrays, sessile or short-pedunculate.
Cypselae

white or brown-streaked, 2.5–3.4 mm, glabrous;

pappi 0.
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.
2n

= 20.

Centaurea calcitrapa
Phenology Flowering summer–autumn (Jun–Nov).
Habitat Pastures, fields, roadsides
Elevation 0–1700 m [0–5600 ft]
Distribution
from FNA
AL; AZ; CA; DC; FL; GA; IA; IL; MA; MD; NJ; NM; NY; OR; PA; UT; VA; WA; ON; Europe; Africa
[WildflowerSearch map]
[BONAP county map]
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. Treatment authors: David J. Keil, Jörg Ochsmann.
Parent taxa Asteraceae > tribe Cardueae > Centaurea
Sibling taxa
C. benedicta, 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. solstitialis, C. stoebe, C. sulphurea, C. virgata, C. ×moncktonii
Name authority Linnaeus: Sp. Pl. 2: 917. (1753)
Web links 
Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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