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caltrops, centaurée chausse-trappe, chausse-trappe, purple knapweed, purple star-thistle, red star-thistle

croix de malte, Maltese knapweed, Maltese star thistle or centaury, Maltese star-thistle, Napa thistle, tocalote

Habit Annuals, biennials, or short-lived perennials, 20–100 cm. Annuals, 10–100 cm, herbage loosely gray-tomentose and villous with jointed multicellular hairs, sometimes minutely scabrous, minutely resin-gland-dotted.
Stems

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

1–few, few–many branched distally.

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.

basal and proximal cauline petiolate or tapering to base, usually absent at anthesis, blades oblong to oblanceolate, 2–15 cm, margins entire to dentate or pinnately lobed;

cauline long-decurrent, blades linear to oblong or oblanceolate, 1–5 cm, entire or dentate.

Involucres

ovoid, 15–20 × 6–8 mm.

ovoid, 10–15 mm, loosely cobwebby-tomentose or becoming glabrous.

Florets

25–40;

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

sterile corollas slender.

many;

corollas yellow, those of sterile florets 10–12 mm, slender, inconspicuous, those of fertile florets 10–12 mm.

Inner phyllaries

appendages truncate, spineless.

appendages entire, acute or spine-tipped.

Heads

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

disciform, 1–few at branch tips, borne singly or in open leafy corymbiform arrays, sometimes clustered in distal axils, sessile or pedunculate.

Cypselae

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

pappi 0.

dull white or light brown, ca. 2.5 mm, finely hairy;

pappi of many white, unequal, stiff bristles 2.5–3 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 ± stramineous, ovate, appendages purplish, spiny-fringed at base, each tipped by slender spine 5–10 mm.

2n

= 20.

= 24.

Centaurea calcitrapa

Centaurea melitensis

Phenology Flowering summer–autumn (Jun–Nov). Flowering mostly spring–summer (Apr–Jul).
Habitat Pastures, fields, roadsides Roadsides, fields, pine-oak woodlands, chaparral, agricultural areas
Elevation 0–1700 m [0–5600 ft] 0–1500 m [0–4900 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]
from FNA
AL; AZ; CA; GA; ID; IL; MA; MO; MS; NJ; NM; NV; OR; PA; TX; UT; WA; WI; BC; Mexico (Baja California); Europe; Asia; Africa [Widely introduced]
[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.)

Centaurea melitensis is native to the Mediterranean region. It is listed as a noxious weed in New Mexico.

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

Source FNA vol. 19, p. 191. Treatment authors: David J. Keil, Jörg Ochsmann. FNA vol. 19, p. 193. Treatment authors: David J. Keil, Jörg Ochsmann.
Parent taxa Asteraceae > tribe Cardueae > Centaurea 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
C. benedicta, C. calcitrapa, C. cyanus, C. depressa, C. diffusa, C. diluta, C. iberica, C. jacea, C. macrocephala, 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) Linnaeus: Sp. Pl. 2: 917. (1753)
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