420 COMPOSITAE. 



Tribe 2. Cynareae. Thistle Tribe. 

 17. CENTAUREA L. Star Thistle. 

 Erecl or diffuse usually rigid annual or biennial herbs with alternate leaves 

 which are not prickly, and medium-sized heads. Involucre ovoid or globose, 

 the bracts imbricated and ending in a needle-like prickle, or at least fringed or 

 toothed (rarely entire) appendage. Receptacle densely bristly, the bristles per- 

 sistent. Flowers yellow or purple, all tubular, the marginal much larger and 

 neutral. Achenes notched just above the base, indicating the oblique or 

 Lateral attachment. Pappus of 2 or 3 rows of bristles or short scales or none. 

 All our species naturalized from Europe. (Named for one of the Centaurs 

 who used it in healing.) 



Flowers yellow; leaves decurrent on the sttm; achenes light gray. 



Plants erect, branching mostly above the base; spines 2 to 4 lines long 



1. C. mclitensis. 



Plants diffuse, branching from the base; spines ]/ 2 to 1 in. long 2. C. solstitialis. 



Flowers purple; leaves not decurrent; achenes brown. 



.Middle bracts ending in a very stout spine; pappus none 3. C. calcitrafa. 



Bracts devoid of spine; pappus present 4. C. salmantica. 



1. C. melitensis L. Napa Thistle. Tocalote. Erect commonly much- 

 branched annual, 1 to 2 ft. high, with a roughish indument, the stems winged 

 by the decurrent leaves; lowest leaves pinnatifid, the upper narrow and mostly 

 entire; heads mostly terminal and solitary, or 2 or 3 together, y. 2 in. high; 

 bracts rigid, the outer with palmatifid spine, the intermediate and inner ones 

 with a rigid spine 2 to 4 lines long which is either simple or with divaricate 

 short spines at base; flowers yellow; pappus-bristles in about 3 rows, the mid- 

 dle row long, the outer and inner very short. 



Abundant everywhere in agricultural lands and pastured hills. First .intro- 

 duced at Napa and diffused over the State in seed grain, hence commonly 

 known as Napa Thistle. Our most widespread and objectionable grain-field 

 weed. May- June. 



2. C. solstitialis L. Barnaby 's Thistle. Diffuse, branching from the 

 base, 1 ft. high, cottony-pubescent ; radical leaves pinnatifid, the cauline 

 linear, entire, rather closely ascending, decurrent into long narrow wings; 

 beads solitary at the ends of the branches, ovoid-globular; bracts much like 

 the preceding except that the spines of the intermediate bracts are 1 in. long 

 or less, and the innermost bracts end in a small shining appendage; flowers 

 very bright yellow; achenes with pappus. 



Cultivated fields, roadsides and waste lands, its aggressive spread continued 

 • luring the last 10 years: Bay region from Sonoma, Napa and Solano cos. north 

 to Live Oak (Sutter Co.). Aug.-Sept. Also called Yellow Star Thistle. 



3. C. calcitrapa L. Purple Star Thistle. Coarse and rigid, forming 

 dense bushy plants, 2 to 4 ft. high, nearly glabrous; leaves pinnately divided 

 into few linear or lanceolate lobes, or the uppermost undivided, :ill serrulate, 

 not decurrenl ; heads large, 1 in. high, on short peduncles scattered along the 

 branches, or in the forks, or terminal; involucral spines very stout, % to 1 

 in. long; flowers purple; achenes brownish, over 1 line long, destitute of 

 pappus. 



Naturalized in bu! a lew places: San Mateo; Vacaville eastward towards 

 Main Prairie. Keeping to uncultivated land. Aug.-Sept. 



4. C. salmantica L. Escobilla. Boughish-hispidulous, the stems nearly 

 glabrous; leaves sinuately divided into triangular lobes below the large terminal 

 ovate or oblong-lanceolate lobe, not decurrenl ; beads on long slender peduncles, 

 under 1 in. high; involucral bracts ovate, obtuse, not spine-tipped, the inner- 





