COMPOSITAE (COMPOSITE FAMILY) 839 



short-ovate or oblong, the inner connate above the middle; rays short or usually 

 none; achenes less roughened. — Neb, and Kan., southw. and westw.; adv. 

 in Mo. 



56. BtDENS L. Bur Marigold 



Heads many-flowered ; the rays when present 3-8, neutral. Involucre 

 double, the outer commonly large and foliaceous. Receptacle flattish ; chaff 

 deciduous with the fruit. Achenes flattened parallel to the bracts of the invo- 

 lucre, or slender and 4-sided (rarely terete), crowned with awns or short teeth 

 (these rarely naked). — Annual or perennial herbs, with opposite various leaves, 

 and mostly yellow flowers, (Latin, bidens, two-toothed.) 



JV. B. — In this genus the measurements of the fruit relate to the inner 

 mature achenes. The outer are often shorter and uncharacteristic. The figures 

 of the heads are on a scale of |, those of the achenes are life size. 



a. Achenes flat (or at most ^vith a sti-ong rib on either face) 6. 

 6. Eays small or wanting- c. 



0. Inner achenes less than 2 mm. broad. 



Heads cylindric or ellipsoid, much longer than broad ; disk-florets 

 8-4 mm. long; leaves simple. 

 Inner achenes 1 cm. or more long ; awns 6-8 mm. long , , \. B. bidentoides. 

 Inner achenes T-9 mm. long ; awns 8-4.5 mm. long . . . 2. B. EatoTii. 

 Heads hemispherical, nearly or quite as broad as long ; disfe-florets 

 1-1.5 mm. long; achenes 5.5-8.5 mm. long; awns 1.5-2.5 mm. 



long ; leaves ternately compound Z. B. Macoidea. 



u. Inner achenes 3 mm. or more broad d. 

 d. Leaves simple ; heads subtended by long thick entire leafy bracts ; 

 achenes 8-10 mm. long, ^-3 mm. broad, retrorsely barbed, 

 the 3 (rarely 2 or 4) awns unequal, at most 6 mm. long . . G. B. comoaa. 

 d. Leaves pinnate; achenes upwardly barbed at least at base; 

 awns 2. 

 Outer Involucre of 5-8 leafy bracts ; inner bracts oblong, 



equaling the disk; achenes 2-3.3 mm. broad . . , 4:. B. frondoaa. 

 Outer involucre of 10-16 leafy bracts ; inner bracts pvate-trian- 



gular, shorter than the disk ; achenes 8.3-4 mm. broad . 5. B. vulgata. 

 b. Rays conspicuously exceeding the disk 6. 



6, Leaves mostly pinnate ; awns (if present) upwardly barbed /. 

 /. Inner achenes 2 mm. or less broad, cuneate. 



Inner achenes 8-4.5 mm. long . .... 11. ^. coronata. 



Inner achenes 5-7 mm. long 12. ^. trickospe^na. 



f. Inner achenes more than 2 mm. broad, elllptic-obovate, with thin 

 scarious margins. 

 Outer foliaceous bracts 8-10, smooth or merely dilate, shorter 



than the inner 18. B. arisioaa. 



Outer foliaceous bracts 12-20, coarsely hispid, mostly longer 



than the inner 14. ^. involuorata. 



e. Leaves simple or slightly divided ; achenes obovate, S-4.5 mm. long, 



with short teeth , . . , 11. B. coronata. 



(A. Achenes angled or terete ff. 

 ff. Achenes distinctly angled ; terrestrial or marsh plants A. 

 /t. Leaves pinnate. ' 



Heads few-flowered, slender ; achenes linear, 4-angled, the inner 



1.2-1.8 cm. long, about 1 mm. broad 10. B. MpinTiata. 



Heads hemispherical, many-flowered ; achenes cuneate, 8-4 angled, 



4-6 ram. long i'i) B. connaia, v, pinnata. 



h. Leaves simple; heads hemispherical, many-flowered; achenes 

 cuneate or obovate. 

 Leaves petioled or with conspicuously narrowed bases; fruiting 



heads erect 7. £. cormata. 



Leaves sessile or connate ; fruiting heads mostly nodding. * 



Outer bracts unequal, mostly exceeding the disk ; rays at most 

 twice the length of the disk ; achenes dilated above ; leaves 



mostly connate 8. -ff. oernua. 



Outer bracts subequal, rarely exceeding the disk ; rays 2-4 times 

 as long as the disk ; achenes not dilated above ; leaves 



sessile, but rarely connate 9. .B. lamia. 



a Achenes terete, truncate at both ends, with the 3-6 very long awns 



smooth below ; aquatic, with the immersed leaves finely divided . 15. B. BeckU. 



1. B. bidentoides (Nutt.) Britton. Glabrous, paniculately branched, 2-8 dm. 



high; leaves lanceolate, coarsely toothed, tapering at both ends; heads 1.5-2 

 gip. long; the outer involucre of '4-5 bracts; rays usually wanting ' '- — 



