GENUS 108. 



THISTLE FAMILY. 



559 



7. Centaurea americana Ntitt. American 

 Star Thistle. Fig. 4662. 



C. americana Nutt. Journ. Phila. Acad. 2: 117. 1821. 



Plectocephalus americanus Don, in Sweet, Brit. Fl. 

 Card. (II) pi. 51- 1831- 



Annual, roughish ; stem stout, simple, or little 

 branched, 2-6 high. Leaves entire or denticu- 

 late, the lower and basal ones spatulate or oblong, 

 2'-s' long, narrowed into petioles, the upper ob- 

 long-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 ; pap- 

 pus of copious unequal bristles longer than the 

 achene. 



Dry plains, Missouri and Arkansas to Louisiana, 

 Mexico and Arizona. May-Aug. 



8. Centaurea Calcitrapa L. Star Thistle. 

 Fig. 4663. 



Centaurea Calcitrapa L. Sp. PI. 917. 1753. 



Annual, pubescent or glabrous, green ; stem 

 much branched, not winged, i-ii high. Leaves 

 i-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 i' broad; invo- 

 lucre 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 Co- 

 lumbia to California. Adventive or naturalized 

 from Europe. Called also caltrops, maize- or mouse- 

 thorn. Knop-weed. June-Oct. 



9. Centaurea melitensis L. Rayless Winged 

 Centaury. Fig. 4664. 



Centaurea melitensis L. Sp. PI. 917. 1753. 



Annual, i-4 high, grayish-pubescent, much branched, 

 the stem and branches narrowly winged by the decur- 

 rent leaf-bases. Basal leaves lyrate, their lobes obtuse ; 

 stem leaves few-lobed or entire, the upper ones i' long 

 or less; heads sessile or nearly so; involucre about 

 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 yel- 

 low, none of them radiant ; pappus scales unequal. 



Waste and cultivated grounds, Georgia to Missouri, Ari- 

 zona, California and Oregon, and in ballast about the 

 Atlantic seaports. Naturalized or adventive from Europe. 

 Widely naturalized in South America. April-Sept. 



