Annuals, 10-100 cm, herbage loosely gray-tomentose and villous with jointed multicellular hairs, sometimes minutely scabrous, minutely resin-gland-dotted. Stems 1-few, few-many branched distally. Leaves: 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. Heads disciform, 1-few at branch tips, borne singly or in open leafy corymbiform arrays, sometimes clustered in distal axils, sessile or pedunculate. Involucres ovoid, 10-15 mm, loosely cobwebby-tomentose or becoming glabrous. Principal phyllaries: bodies ± stramineous, ovate, appendages purplish, spiny-fringed at base, each tipped by slender spine 5-10 mm. Inner phyllaries: appendages entire, acute or spine-tipped. Florets many; corollas yellow, those of sterile florets 10-12 mm, slender, inconspicuous, those of fertile florets 10-12 mm. Cypselae dull white or light brown, ca. 2.5 mm, finely hairy; pappi of many white, unequal, stiff bristles 2.5-3 mm. 2n = 24. Flowering mostly spring-summer (Apr-Jul). Roadsides, fields, pine-oak woodlands, chaparral, agricultural areas; 0-1500 m; widely introduced; B.C.; Ala., Ariz., Calif., Ga., Idaho, Ill., Mass., Miss., Mo., Nev., N.J., N.Mex., Oreg., Pa., Tex., Utah, Wash., Wis.; Mexico (Baja California); Europe; Asia; Africa. Centaurea melitensis is native to the Mediterranean region. It is listed as a noxious weed in New Mexico.
FNA 2006, Kearney and Peebles 1969
Duration: Annual Nativity: Non-Native Lifeform: Forb/Herb General: Introduced, invasive annual, 1-10 dm, gray-hairy. Leaves: Resin dotted, more or less scabrous, lower leaves 2-15 cm, entire to lobed, general 0 at flower; cauline long-decurrent. Flowers: Heads 1-few, involucre 10-15 mm, ovoid, more or less cobwebby or becoming glabrous; main phyllaries straw-colored, appendage purplish, base spine-fringed, central spine 5-10 mm, slender; many flowers; corollas 10-12 mm, equal, yellow, sterile corollas slender. Fruits: Cypselae 2.5 mm, light brown, finely hairy, pappus bristles 2.5-3 mm, white. Ecology: Found on waste ground and open sites or disturbed ground below 7,500 ft (2286 m); flowers May-June. Distribution: Introduced to western N. Amer. , from B.C. south to CA and west to TX; south to S. Amer.; also in Africa, Australia and Europe. Notes: Invasive weed often associated with agriculture and roads. Distinguished by being densely hairy all over, the spine-tipped phyllaries; and the yellow corollas. Ethnobotany: Used medicinally for the kidneys. Etymology: Centaurea is a Latin reference to the Centaur Chiron, while melitensis means of or from Malta. Synonyms: None Editor: SBuckley 2010, FSCoburn 2015
Annual 1.5-7 dm, lightly arachnoid when young and with some more persistent coarser crisp hairs; stem narrowly winged by the decurrent lf-bases; basal and lower cauline lvs oblanceolate, toothed to lyrate-pinnatifid, 3-15 cm נ5-35 mm, usually deciduous; middle and upper lvs smaller, becoming linear-oblong and entire; invol 8-15 mm, broad-based, its middle and outer bracts slenderly spine-tipped, the central spine 5-9 mm; inner bracts weakly spinose or merely tapering, not at all enlarged apically, generally purple-tinged; fls yellow; pappus 1.5-3 mm; 2n=24, 36. A weed in waste places; native of the Mediterranean region, occasionally found in our range. June-Sept.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.