Bidens L.

Herbs, erect or diffuse, glabrous or hairy, rarely shrubby. Stems tetragonous, branched, mostly pubescent, striate or sulcate. Leaves opposite, simple or compound or bipinnatisect, entire, toothed. Heads homo or heterogamous, discoid or radiate, solitary or in corymbose-panicles. usually pedunculate. Involucre campanulate, biseriate, shortly connate at the base; outer involucral bracts herbaceous or leafy; inner membranous, with scarious margins. Receptacle flat or convex. Ray florets white or yellow, sterile or absent. Disc florets yellow, fertile, 5-lobed. Anthers often black. Style branches flattened, apically pilose with a short, narrow appendage. Achenes black or brown, narrowly fusiform or linear, tetragonous, truncate and erostrate at the apex. Pappus of 2 - 4 stiff, smooth or retrorsely barbed bristles.

Distributed throughout the world; ca 230 species l0 in India.

Literature. SHERFF. E.E. (1916 & 1928). Studies in the genus Bidens III. Bot. Gaz. 61: 495-506. 1916; VIII. 85: 1-29; IX. 86: 435-447. SHERFF, E.E. (1937). The genus Bidens in Field. Mus. Nal. Hist. Bot. Ser. 16: 1-709

KEY TO THE SPECIES

1a. Leaves simple

2

b. Leaves pinnately lobed

5

2a. Leaves petiolate; pappus awns 3

4. Bidens comosa

b. Leaves sessile; pappus awns 2-4

3

3a. Pappus awns equal, retrorsely barbed

3. Bidens cernua

b. Pappus awns unequal, smooth

4

4a. Leaves up to 1 cm long, entire; margins of achenes smooth

6. Bidens minima

b. Leaves up to 10 cm long, serrate; margins of achenes retroserrate

9. Bidens tetraspinosa

5a. Leaves ternate or imparipinnate or pinnatipartite

6

b. Leaves deeply pinnatisect

9

6a. Outer involucral bracts leafy, 10-40 mm long; achenes cuneate with retrorse setae along the margins

10. Bidens tripartita

b. Outer involucral bracts linear or narrowly spathulate, 3-8 mm long; achenes linear, glabrous or more or less hispid in the upper part

7

7a. Leaves 3-5 partite or undivided; outer involucral bracts narrowly spathulate

7. Bidens pilosa

b. Leaves pinnate or bipinnate; outer involucral bracts linear or linear-lanceolate

8

8a. Leaves pinnate; leaflets deltoid-ovate; heads 5-8 mm accross

2. Bidens biternata

b. Leaves bipinnate; leaflets lanceolate; heads 3-5 mm accross

1. Bidens bipinnata

9a. Tall herbs, 50-100 cm high; achenes, 10-20 mm long, with linear, ascending-strigoae beak

8. Bidens sulphurea

b. Small herbs, 15-25 cm; achenes 5-9 mm long, without a beak

5. Bidens humilis

List of Lower Taxa