GENUS 108, THISTLE FAMILY. 209 
7. Centaurea americana Nutt. American 
Star Thistle. Fig. 4662. 
C. americana Nutt. Journ. Phila. Acad. 2: 117. 1821, 
Plectocephaius americanus Don, in Sweet, Brit. Fl. 
Gard. (II) pl. 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’-5’ 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, 
Tfexico and Arizona. May-—Aug. 
RW, . | 
WES 8. Centaurea Calcitrapa L. Star Thistle. 
TRS Fig. 4663. 
Centaurea Calcitrapa L. Sp. Pl. O17, 9753. 
Annual, pubescent or glabrous, green; stem 
much branched, not winged, 1°-13° 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 1’ 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- 
jo 
lumbia to California. Adventive or naturalized 
from Europe. Called also caltrops, maize- or mouse- 
thorn. Knop-weed. June-Oct. 
g. Centaurea meliténsis L. Rayless Winged 
Centaury. Fig. 4664. 
Centaurea melitensis L. Sp. Pl. 917. 1753. 
Annual, 1°-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 1’ long 
or less; heads sessile or nearly so; involucre about 3’ 
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. 
