20. Centaurea sulphurea Willdenow, Enum. Pl. 930. 1809.
Sicilian star-thistle, sulphur-colored Sicilian thistle, sulphur knapweed
Centaurea bovina. J. T. Kartesz and C. A. Meacham (1999) listed C. bovina Velenovský from Massachusetts, referencing Rhodora 1924, perhaps based on collections reported as C. diffusa from Norfolk County (C. H. Knowlton and W. Deane 1924). Knowlton and Deane made no mention of C. bovina. According to J. Dostál (1976), C. bovina differs from C. diffusa in having smaller involucres (6–7 mm versus 7–10 mm; 3.5 mm versus 4–5 mm diameter), and purple versus pink flowers). Examination of one of the Norfolk County collections (Churchill s.n., MIN) revealed no differences from C. diffusa.
Centaurea paniculata. According to our herbarium studies, reports of C. paniculata Linnaeus (Jersey knapweed) from North America are apparently referable to C. stoebe subsp. micranthos. Centaurea paniculata is quite similar to C. stoebe in habit; it differs clearly by its narrowly ovoid or cylindric heads.
Annuals, 10–100 cm. Stems simple to openly branched, branches ascending, villous to hispid with septate hairs and loosely tomentose. Leaves ± 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. Heads disciform, borne singly or in open, few-headed corymbiform arrays, long-pedunculate. Involucres ovoid, 12–30 mm, distally constricted. Principal 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. Inner phyllaries: appendages acute or spine-tipped. Florets many; corollas yellow, all ± equal, 25–35 mm; corollas of sterile florets slender, inconspicuous. Cypselae dark brown, 5–8 mm, glabrous; pappi of many, brown to blackish, unequal bristles 6–7 mm. 2n = 24.
Flowering spring–summer (May–Jul). Disturbed sites, grasslands, woodlands, pastures, roadsides; 0–300 m; Calif.; sw Europe.
Centaurea sulphurea is considered to be a noxious weed by the state of California.
According to R. Angelo (pers. comm.), "The Kartesz citation is puzzling. This taxon [C. bovina] is not cited in the 1924 volume of Rhodora or anywhere in the first 50 years of Rhodora according to the index for that volume and our 50 year index (which is quite comprehensive).
"Also, there are no specimens identified as this taxon in the New England Botanical Club (NEBC) herbarium or from Massachusetts in the Harvard University Herbaria collections. We also looked for re-identifications in the other taxa in Centaurea in the NEBC and found no specimens that were earlier identified as C. bovina.
"The Vascular Plants of Massachusetts[...] (1999) of [B. A.] Sorrie and [P.] Somers does not list this taxon, nor does the Flora of the Northeast[...] (1999) by [D. W.] Magee and [H. E.] Ahles."