COMPOSITAE (COMPOSITE FAMILY) 551 



the angles more or less corky. B. chrysanthemoides; it has passed also as 

 B. cernua L. Common in wet ground throughout our range. 



2. Bidens comosa (Gray) Wieg. Bull. Torr. Bot. Club 24: 436. 1897. Stem 

 stout, 3-8 dm. high: leaves elliptic-lanceolate, serrate, acute, attenuate into 

 a margined petiole, or the upper sessile: peduncles short and stout: outer 

 bracts of the involucre 6-8, often 2-5 times the length of the disk, erect: rays 

 wanting: disk-corollas funnelform, pale yellow, 4-lobed: achenes large and 

 flat, 8-10 mm. long, 3 mm. wide, brown or olive, the 3 long awns retrosely 

 barbed. In damp soil; Maine to Colorado and Louisiana. 



3. Bidens frondosa L. Sp. 832. 1753. Stem slender, bushy-branched, 

 nearly glabrous, 3-8 dm. high: leaf-blades pinnately 3-divided or rarely 5- 

 divided, the segments lanceolate, serrate, with sharp spreading teeth, acumi- 

 nate: heads not large; outer bracts of the involucre 6-8, subequal, spatulate, 

 sparsely ciliate, usually exceeding the disk: rays usually present, golden- 

 yellow, the ligules equaling the disk, the ovaries hairy and with 2 short re- 

 trorsely barbed awns: disk-corollas orange, 5-lobed: achenes black, about 6 

 mm. long and 3 mm. wide, cuneate, flattish; barbs on the 2 awns either erect 

 or reflexed. Common eastward and extending into our range. 



4. Bidens vulgata Greene, 1. c. 72. Stem tall, branched, nearly glabrous: 

 leaf-blades commonly 5-divided, the segments lanceolate, acute, serrate: 

 heads large, 15-25 mm. wide; outer bracts of the involucre 8-16, unequal, 

 usually longer than the disk, ciliate, with narrowed tips: rays pale yellow, 

 the ligules equaling the disk, the ovaries awnless; disk-corollas funnelform, 

 pale, 4-5-1 obed: achenes 7-9 mm. long, very flat, brown or olive, the 2 long 

 awns and the upper part of the achene-margins retrorsely barbed. Closely 

 allied to the preceding, more frequent as a weed and the more common form 

 in our range. 



5. Bidens tenuisecta Gray, PI. Fendl. 86. 1848. Stems 3-6 dm. high, 

 branched from the base, sparsely hirsute or glabrous: leaves 2-3-ternately or 

 pinnately dissected into narrow linear lobes: heads on naked rather long and 

 stout peduncles, many-flowered, 8-12 mm. high in flower: achenes glabrous, 

 2-awned; inner 10 mm. long, with tapering summit; outermost 6 mm. long, 

 stouter and with broad summit and usually short awns: rays yellow, mostly 

 surpassing the disk. Along water courses; Colorado, New Mexico, and 

 Arizona. 



6. Bidens bipinnata L. Sp. PI. 832. 1753. Stem glabrous, 4-angled, 

 branched, slender, 3-10 dm. high: primary leaf-segments thin, deltoid, the 

 ultimate one lanceolate, incised or lobed: outer involucral bracts 7-10, linear, 

 shorter than the acute inner ones: rays few, the ligules yellowish-white, about 

 equaling the disk, mostly entire: achenes spindle-shaped, in fruit much longer 

 than the involucre, the outer slightly shorter; awns 3-4, yellow, retrorsely 

 barbed. (B. Bigelovii Gray, as to our range at least.) Damp soil and waste 

 grounds; a common and disagreeable weed, widely dispersed ; usually known 

 as SPANISH NEEDLES. 



58. THELESPERMA Less. 



Smooth and glabrous perennials, with opposite usually finely dissected 

 leaves, pedunculate heads, and the rays golden-yellow (if present). Bracts 

 of the inner involucre united into a cup; outer of shorter and narrow bracts, 

 connate at base with the inner. Chaff of the flat receptacle white-scarious. 

 Rays about 8, cuneate-obovate. Disk-corollas with long and slender tube, 

 and abrupt campanula te or cylindrical throat. Anthers wholly exserted. 

 Achenes slightly obcompressed or terete, narrowly oblong to linear, margin- 

 less, beakless; the abrupt summit crowned with a pair of persistent and 

 stout awns or scales, or sometimes pappus wanting. 



Heads rayless (discoid) 1. T. gracile. 



Heads radiate. 



Leaves linear; plant perennial. 



Leafy throughout ; pappus evident 2. T. ambiguum. 



