. 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. BIDENS L. Bdr 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 llowers. (Latin, bidens, two-toothed.) 



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

 n)ature 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 with a strong rib on either face) 6. 

 h. Kays small or wanting' c. 

 c. Inner achenes less than 2 mm. broad. 



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

 3— i ram. long ; leaves simple. 

 Inner achenes 1 cm. or more long ; awns 6-8 mm. long , . 1. .5. bidenioides. 

 Inner achenes 7-9 mm. long; awns 8-i.5 mm. long . . . 2. £. Eatoni. 

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

 1-1.5 mm. long ; achenes 5.5-S.5 mm. long ; awns 1.5-2.5 mm. 



long; leaves ternately compound 3. B. discoidea. 



c. Inner achenes 2 mm. or more broad d. 

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

 achenes S-IU mm. long, 2-3 mm. broad, retrorsely barbed, 

 the 3 (rarelj- i or 4) awns unequal, at most 6 mm. long . . &. B. comosa. 

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

 awns 2. 

 Outer involucre of 5-S leafy bracts ; inner bracts oblong, 



equaling the disk ; achenes 2-3.3 mm. broad . . . i. B. frondosa. 

 Outer involucre of 10-10 leafy bracts ; inner bracts ovate-trian- 

 gular, shorter than the disk ; achenes 3.3-4 mm. broad . 5, B. 'culgata. 

 b. Ea}'s conspicuously exceeding the disk e. 



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

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



Inner achenes 3-4.5 mm. long 11. ^. coronata. 



Inner achenes .5-7 mm. long 12,. B, trichosperm<i, 



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

 scarious margins. 

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



than the inner 13. 5. aristosa. 



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



than the inner 14. ^. involucrata. 



e. Leaves simple or slightl}- divided ; achenes obovate, 3-4.5 mm, long, 



•with short teeth 11. .B. coronata, 



a. Achenes angled or terete g. 

 g. Achenes distinctly angled ; terrestrial or marsh plants h. 

 h. Leaves pinnate. 



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



1.2-1.8 cm. long, about 1 mm. broad 10. 5. hipinnaia. 



Hea<is hemispherical, many-flowered ; achenes cuneate, 3-4 angled, 



4-6 mm. long . " (7) ^. connata, v. pintiaia. 



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



cuneate or obovate. 

 " Leaves petioled or with conspicuously narrowed bases ; fruiting 



heads erect * 1. B, connata. 



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 %. B. cerntta. 



Outer bracts subequal, rarely exceeding the disk ; raj's 2-4 times 

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



sessile, but rarely connate 9. B. la&vis. 



g. Achenes terete, truncate at botli ends, with the ;3-6 ver}' long awns 



smooth below: aquatic, with tlic iinmorsed leaves finely divided . 15. B. Beckii. 



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

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

 cm. long ; the outer involucre of 4-5 bracts ; rays usually wanting ; achenes 



