Centaurea diffusa
Centaurea sulphurea
centaurée diffuse, diffuse knapweed, diffuse or tumble or white knapweed, tumble knapweed, white knapweed
Sicilian star-thistle, sulphur knapweed, sulphur-color Sicilian thistle
1–several, much-branched throughout, puberulent and ± gray tomentose.
simple to openly branched, branches ascending, villous to hispid with septate hairs and loosely tomentose.
hispidulous and ± short-tomentose;
basal and proximal cauline petiolate, often absent at anthesis, blades 10–20 cm, margins bipinnately dissected into narrow lobes;
mid cauline sessile, bipinnately dissected;
distal much smaller, entire or pinnately lobed.
± villous to hispid with septate hairs, minutely resin-gland- dotted;
basal winged-petiolate, blades oblong to oblanceolate, 10–15 cm, margins pinnately lobed, lobes acute, finely dentate;
cauline sessile, long-decurrent with narrow wings, linear-oblong to oblanceolate, 1–6 cm, entire or distally serrate with short, spine-tipped teeth.
narrowly ovoid or cylindric, 10–13 × 3–5 mm.
ovoid, 12–30 mm, distally constricted.
25–35;
corollas cream white (rarely pink or pale purple), those of sterile florets 12–13 mm, slender, inconspicuous, those of fertile florets 12–13 mm.
many;
corollas yellow, all ± equal, 25–35 mm;
corollas of sterile florets slender, inconspicuous.
lanceolate, ± acute, appendage lacerate or spine-tipped.
appendages acute or spine-tipped.
disciform, in open paniculiform arrays.
disciform, borne singly or in open, few-headed corymbiform arrays, long-pedunculate.
dark brown, ca. 2–3 mm;
pappi 0 or less than 0.5 mm, only rudimentary.
dark brown, 5–8 mm, glabrous;
pappi of many, brown to blackish, unequal bristles 6–7 mm.
phyllaries: bodies pale green, ovate to lanceolate, glabrous or finely tomentose, with a few prominent parallel veins, margins and erect appendages fringed with slender stramineous spines, each phyllary tipped by spine 1–3 mm.
phyllaries: bodies greenish or stramineous, ovate to elliptic, glabrous, appendages spreading to reflexed, brown to blackish purple, each with palmately radiating cluster of spines, central spine stout, 1–2.5 cm, base dark brown to black, distally stramineous.
= 18, 36.
= 24.
Centaurea diffusa
Centaurea sulphurea
Centaurea diffusa is native to southeastern Europe and casually adventive in central and western Europe.
Centaurea diffusa readily hybridizes with C. stoebe subsp. micranthos and is often confused with their fertile hybrid (C. ×psammogena G. Gáyer); the latter can be recognized by its cypselae bearing pappi and having conspicuously radiant heads. Morphologically the hybrids are extremely variable; they may be intermediate or may closely resemble one or the other of the parents. Conspicuously radiant heads and pappi are always present; appendages of the phyllaries are brown to black, or rarely stramineous; spines are absent or short and 2n = 18. Centaurea ×psammogena is known from waste places, roadsides, railway tracks; 50–2500 m; B.C., Ont., Que.; Colo., Mass., Mich., Mo., N.C., Oreg., Tenn., Wash. It may occur spontaneously where the ranges of the parent species overlap; they may also be distributed separately. In mixed stands it replaces C. diffusa by introgression. Hybrids are often misidentified as C. diffusa.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Centaurea sulphurea is considered to be a noxious weed by the state of California.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
- Local floras:
BC, 
CA, 
OR, 
WA - Local Web sites: CalFlora, CalPhotos,
Flora NW, 
Go Botany, 
IL Wildflowers, 
MI Flora, 
MO Plants, 
PNW Herbaria, Turner Photog. 
WildflowerSearch
iNaturalist (observations)
USDA Plants Database- LBJ Wildflower Center
- SEINet
- Plants of the World Online
- Encyclopedia of Life
- Wikipedia
- Google Image Search
