7.
Helianthus debilis
Nuttall, Trans. Amer. Philos. Soc., n. s. 7: 367. 1841.
Annuals or perennials
, 30—200 cm (taprooted).
Stems
decumbent to erect, glabrous, hirsute, or puberulent.
Leaves
mostly cauline; mostly alternate; petioles 1—7 cm; blades deltate-ovate, lance-ovate, or ovate, 2.5—14 × 1.8—13 cm, bases cordate to truncate or broadly cuneate, margins subentire to serrate, abaxial faces glabrate to hispid, not gland-dotted.
Heads
1—3.
Peduncles
9—50 cm.
Involucres
hemispheric, 10—22 mm diam.
Phyllaries
20—30, lanceolate, 8—17 × 1—3 mm, apices acute to long-attenuate, abaxial faces glabrous or ± hispid, not gland-dotted.
Paleae
7.5—8 mm, apices 3-toothed (middle teeth acuminate, usually glabrous or hispid, sometimes ± villous or bearded).
Ray florets
11—20; laminae 12—23 mm.
Disc florets
30+; corollas 4.5—5 mm, lobes usually reddish, sometimes yellow; anthers dark, appendages dark (style branches usually reddish, rarely yellow).
Cypselae
2.5—3.2 mm, glabrous or sparsely hairy;
pappi
of 2 lanceolate or lance-linear scales 1.2—2.5 mm.
Subspecies 5 (5 in the flora): United States (Atlantic and Gulf coasts).
C. B. Heiser (1956) placed 8 subspecies in
Helianthus debilis
; he noted that alternative taxonomic treatments might recognize these in as many as three species, or expand the single species to include
H. petiolaris
. Later, Heiser et al. (1969) separated three of the subspecies as
H. praecox
. Isozyme data (R. P. Wain 1982, 1983; L. H. Rieseberg and M. F. Doyle 1989) show that all are closely related. Documented hybridization with
H. annuus
further complicates the situation. The treatment by Heiser et al. is followed here.
Helianthus debilis
is adventive beyond the Atlantic and Gulf coasts of the United States.
