Flora of North America species comparison

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Centaurea calcitrapa

Centaurea phrygia

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

wig knapweed
Habit Annuals, biennials, or short-lived perennials, 20–100 cm. Perennials, 15–80 cm.
Stems

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

few–many, erect, simple or branched.
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.

± arachnoid-tomentose;

basal and proximal cauline winged-petiolate, blades lanceolate to ovate, 3–15 cm, margins entire or dentate;

distal cauline sessile, sometimes clasping, not decurrent, well developed.
Involucres

ovoid, 15–20 × 6–8 mm.

ovoid to ± spheric, 15–20 mm.
Florets

25–40;

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

sterile corollas slender.

many, the peripheral sterile;

corollas pink or purple, those of sterile much expanded and exceeding corollas of fertile florets, those of fertile 20–25 mm.
Inner phyllaries

appendages truncate, spineless.

tips erect, ovate or orbiculate, irregularly dentate or lobed.
Heads

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

usually radiant, usually borne singly.
Cypselae

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

pappi 0.

tan, 3–4 mm, finely hairy;

pappi 0 or of many unequal bristles 0.5–2 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 lanceolate to ovate, loosely tomentose or glabrous, appendages brown or blackish, lanceolate to ovate, ± covering bodies of adjacent phyllaries, tips often recurved, elongate, featherlike, pectinately dissected into long, filiform lobes.
2n

= 20.

= 22 (Russia), 44 (Slovenia).

Centaurea calcitrapa

Centaurea phrygia
Phenology Flowering summer–autumn (Jun–Nov). Flowering summer (Jul–Sep).
Habitat Pastures, fields, roadsides Disturbed sites
Elevation 0–1700 m [0–5600 ft] 100–300 m [300–1000 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
FL; IL; MO; NJ; NY; OH; PA; VA; VT; WV; Europe [Introduced in North America]
[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.)

According to R. J. Moore (1972), reports of Centaurea nervosa Willdenow [C. uniflora Turra subsp. nervosa (Willdenow) Bonnier & Layens] from New York were based on a specimen referable to C. phrygia subsp. phrygia. Moore called these plants C. austriaca Willdenow, which J. Dostál (1976) treated as a synonym of C. phrygia subsp. phrygia.

Specimens of Centaurea phrygia are sometimes misidentified as C. nigrescens (or one or another of its synonyms) or as C. nigra. The elongate, often recurved, setose-ciliate tips of the phyllary appendages are a readily recognizable characteristic of this species. Considerable morphologic variation occurs in vegetative features and head dimensions in American material of the species, and it is possible that one or more of the specimens we have identified as C. phrygia represent an extreme variant of one of the members of the C. jacea complex. J. Dostál (1976) recognized 10 subspecies of C. phrygia in Europe. We have chosen not to assign the sparse North American material to subspecies.

(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. 188. 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. melitensis, C. montana, C. nigra, C. nigrescens, C. scabiosa, C. solstitialis, C. stoebe, C. sulphurea, C. virgata, C. ×moncktonii
Synonyms C. austriaca
Name authority Linnaeus: Sp. Pl. 2: 917. (1753) Linnaeus: Sp. Pl. 2: 910. (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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