502 COMPOSITE. 



toothed, sagittately clasping at base, with acute lohes; lower leaves 

 petioled; uppermost sessile and commonly lanceolate; heads about f 

 in. broad when expanded; acbenes longitudinally ribbed and ti'ans- 

 versely rugose. 



Naturalized European weed: old fields and waste places, flowering 

 at all seasons. 



2. S. asper L. Prickly Sow-thistle. Very similar to the 

 preceding, but the leaves sometimes undivided and commonly clasp- 

 ing by an auricled base, the auricles rounded; acbenes fiat, margined 

 with a narrow wing and marked on each side with 3 longitudinal 

 ribs; intervals between the ribs smooth, but the ribs as well as the 

 marginal wing rugulose or serrulate; peduncles conspicuously hirsute 

 with spreading gland-tipped hairs. 



Naturulized European weed: with the preceding but apparently 

 not so com-mon. There are hybrid-like intermediates. 



Tribe 2. Cynareae. Thistle Tribe. 



17. CENTAUREA L. Star Thistle. 

 Erect or diffuse usually rigid annual or biennial herbs with alter- 

 nate leaves which are not prickly, and medium-sized heads. Involu- 

 cre 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 persistent. Flowers yellow or 

 purple, all tubular, the marginal much larger and neutral. Acheres 

 notched just above the base, indicating the oblique or lateral attach- 

 ment. 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 stem; achenes light gray. 

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



1. C. Melitensis. 

 Plants diffuse, branching from the base; spines J^ to 1 in. long . . 



2. C. solstitialis. 

 Flowers purple; leaves not decurrent; acbenes brown. 



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

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



1. C. Melitensis L. Napa Thistle. Tocalote. Erect com- 

 monly much-branched annual, 1 to 2 ft. high, with a roughish 

 induraent, the stems winged by the decurrent leaves; lowest leaves 

 pinnatifld, the uppernarrow and mostly entire; heads mostly terminal 

 and solitary, or 2 or 3 together, J 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 

 middle row long, the outer and inner very short. 



Abundant everywhere in agricultural lands and pastured hills. 

 Probably first introduced at Napa and diffused over the state in seed 



frain, hence commonly known as Napa Thistle. May-June, or the 

 ead plants persisting through the autumn into early winter, the 



