Helianthus 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 : 141

45. Helianthus L. 2

Stout annual or perennial herbs. Leaves simple, the lower opposite, the others usually alternate. Capitula large. Involucral bracts imbricate, in 2 to several rows, herbaceous. Receptacle flat or slightly convex, with scales which partly enclose the achenes. Outer florets ligulate, sterile, yellow. Inner florets hermaphrodite; corolla shortly 5-lobed. Achenes somewhat compressed and angled; pappus of 2 deciduous setae and rarely some small scales.

Some species and hybrids, in addition to those described below, occur as escapes from cultivation, and may be in process of becoming naturalized. The commonest of these are the annuals H. debilis Nutt. , Trans. Amer. Philos. Soc. nov. ser., 7: 367 (1841) and H. petiolaris Nutt. , Jour. Acad. Nat. Sei. Philad. 2:115 (1821) and the perennials H. decapetalus L., Sp. Pl. 905 (1753), H. rigidus (Cass.) Desf. , Cat. Pl. Horti Paris, ed. 3, 184 (1829), H. strumosus L., Sp. Pl. 905 (1753), and H. annuus x decapetalus .

Literature: C. B. Heiser, Mem. Torrey Bot. Club 22(3): 1-218 (1969).

1 Annual; receptacle flat or nearly so 1. annuus

1 Perennial; receptacle convex

2Involucral bracts at least as long as the diameter of the disc, narrow, ±patent; upper leaves not much smaller than lower; rhizomes tuberous 2. tuberosus

2Involucral bracts shorter than the diameter of the disc, wide, appressed; upper leaves usually much smaller than lower; rhizomes not tuberous 3. x laetiflorus