This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol3", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
C. maculosa Lam. Encycl. 1: 669. 1783.
Annual or biennial, loosely floccose-pubescent or glabrate, usually much branched, 2°-3° high, the stiff branches ascending. Leaves pinnatifid into linear segments, or the upper linear and entire, the lower up to 3' long; heads peduncled, about 10" broad; involucre ovoid, its ribbed bracts pectinate only at the black tip, the inner ones longer than the outer and entire or merely erose; corollas white to purple, the marginal ones radiant.
Waste grounds, Massachusetts to New Jersey and Pennsylvania. July-Aug.
Annual, roughish; stem stout, simple, or little branched, 2°-6° high. Leaves entire or denticulate, the lower and basal ones spatulate or oblong, 2'-5' long, narrowed into petioles, the upper oblong-lanceolate, sessile, mucronate; heads solitary at the much thickened ends of the leafy stem or branches, very showy, 2'-4' broad; involucre nearly hemispheric, its bracts ovate or lanceolate with conspicuously pectinate appendages; flowers pink or purple, the marginal ones with enlarged and radiant corolla-limbs; achenes somewhat compressed, obliquely attached at the base; pappus of copious unequal bristles longer than the achene.
Dry plains, Missouri and Arkansas to Louisiana, Mexico and Arizona. May-Aug.
Centaurea Calcitrapa L. Sp. Pl. 917. 1753.
Annual, pubescent or glabrous, green; stem much branched, not winged, i°-i 1/2° high. Leaves 1-2-pinnatifid into oblong-lanceolate to linear, serrulate-spinulose, dentate or entire mostly acute lobes, the upper sessile and slightly clasping, the lower and basal short-petioled, 4'-7' long, the uppermost somewhat involucrate at the bases of the sessile heads which are about 1' broad; involucre ovoid, its outer bracts ovate-oblong, tipped with stout, spreading, yellowish spines which are simple, or commonly with 2-6 bristles at the base; flowers purple, none of them radiant; achenes compressed or obscurely 4-sided; pappus none.
In waste places and ballast, southern New York and New Jersey to Virginia. Also from British Columbia to California. Adventive or naturalized from Europe. Called also caltrops, maize- or mouse-thorn. Knop-weed. June-Oct.
Centaurea melitensis L. Sp. Pl. 917. 1753.
Annual, 1°-4° high, grayish-pubescent, much branched, the stem and branches narrowly winged by the decurrent leaf-bases. Basal leaves lyrate, their lobes obtuse; stem leaves few-lobed or entire, the upper ones 1' long or less; heads sessile or nearly so; involucre about V thick, its principal bracts tipped by a slender purplish divergent spine 5" long or less, which is often branched below and with smaller spines at its base; flowers yellow, none of them radiant; pappus scales unequal.
Waste and cultivated grounds, Georgia to Missouri, Arizona, California and Oregon, and in ballast about the Atlantic seaports. Naturalized or adventive from Europe. Widely naturalized in South America. April-Sept.
Centaurea solstitialis L. Sp. Pl. 917. 1753.
Annual, cottony-pubescent, branched, 1°-2° high, the stem and branches winged by the decurrent leaf-bases. Basal leaves pinnatifid, often 6' long; stem leaves lanceolate to linear, mostly entire, the upper 1/2'-l' long; involucre ovoid-globose, about 1/2' thick, its principal bracts tipped by a stout, spreading or reflexed yellow spine, 6"-10" long, with several much smaller ones at its base; flowers yellow, none radiant.
Waste and cultivated grounds, Massachusetts to New York, Pennsylvania, Ontario and Utah, and in California. Adventive from Europe. July-Sept.