Bidens L.

Tutin, T. G., Heywood, V. H., Burges, N. A., Moore, D. M., Valentine, D. H., Walters, S. M. & Webb, D. A., 1976, Flora Europaea. Volume 4. Plantaginaceae to Compositae (and Rubiaceae), Cambridge University Press : 139

41. Bidens L. 1

Annual or perennial herbs. Leaves opposite, entire to 2-pinnatisect. Capitula solitary, usually pedunculate. Involucral bracts in 2 rows, the outer usually herbaceous and often leaf-like, the inner membranous, often with a scarious margin. Receptacle flat or slightly convex, with scales. Ligulate florets usually absent, rarely in 1 row, sterile; tubular florets hermaphrodite. Achenes obovoid-oblong or linear, compressed or somewhat 4-angled, usually with setose margins; pappus of 2-5, usually retrorsely hispidulous or aculeate setae.

Literature: E. E. Sherff, Pubi. Field Mus. Bot. (Chicago) 16(1):

1-346; 16(2): 347-709 (1937). 1 At least the lower leaves pinnate, with petiolulate pinnae

2 Pinnae lobed almost to the midrib; achenes longer than the inner involucral bracts

3 Leaf-lobes rhombic to broadly lanceolate; pappus-bristles 2-4 mm, erecto-patent at maturity 8. bipinnata

3 Leaf-lobes mostly linear-lanceolate; pappus-bristles 1-2-5 mm, erect at maturity 9. subaltemans

2 Pinnae unlobed; achenes about equalling the inner involucral bracts, rarely longer

4 Capitula c. 20 mm in diameter; achenes oblong 6. frondosa

4 Capitula c. 10 mm in diameter; achenes fusiform 7. pilosa

1 Lower leaves simple or lobed, but lobes not petiolulate

5 Peduncles recurved just below the capitula; achenes with a convex, cartilaginous apex 5. cernua

5 Peduncles not recurved; achenes with a flat or concave, not cartilaginous apex

6Outer involucral bracts never leaf-like; ligules 10-30 mm, always present; marginal setae of achenes erect 4. aurea

6Outer involucral bracts usually leaf-like; ligules not more than 10 mm, usually absent; marginal setae of achenes deflexed

7 Capitula with 10-12 outer involucral bracts; achenes 3-4 mm, with 2 bristles 3. radiata

7 Capitula with (2-)5-8 outer involucral bracts; achenes with (2)3-5 bristles

8 Central achenes flat 1. tripartita

8 Central achenes strongly 4-angled 2. connata