Sunflowers (Helianthus)

Groups:

..... group:..........
receptacle flat (annual) Group I
receptacle convex or low-conic (perennial): .....
lvs very narrow Group II
lvs wider:  
involucre bracts imbricate, broad, firm, appressed, rounded to sharply acute Group III
involucre bracts narrow, seldom much imbricate, some or all w/ loose, acuminate or attenuate tip; disk yellow: .....
stem hairy below as well as in the infl Group IV
stem essentially glabrous below the infl, often also glaucous .....
heads small, the disk mostly 0.5-1.5cm wide, rays 5-10 Group V

heads larger, the disk 1.5-3.5cm, rays 10-25

 .....
petiole short (seldom much as 1cm or none) Group VI
petiole longer, commonly 1-4cm on well-developed lvs Group VII

Group I

..... stem hairy; narrow lvs stem hairy, wide lvs
central receptacular bracts inconspicuously short-hairy; invol bracts chiefly ovate or ovate-oblong, abruptly contracted above ...... common sunflower (1.annuus) weed in disturbed sites, esp in moist wet ground; throughout
central receptacular bracts white-bearded at the tip; invol bracts narrower, tapering plain sunflower (2.petiolaris) prairies, plains & waste pls, esp in sandy soil; Great Plains and occ. adventive eastward .....

Group II

narrow-lvd sunflower (21. angustifolius) swamps & moist places; L.I. south

Group III

.... stem glabrous; narrower lvs stem glabrous; wider lvs
disk red-purple (15. H. x laetiflorus) roadsides & other disturbed sites; an escape scattered in e & mw US .....
disk yellow ..... stiff sunflower (14.pauciflorus) prairies & roadsides, occ.eastward

Group IV

..... stem hairy, narrow lvs stem hairy, wide lvs
heads large; petiole short or sessile tall s.f. (17.giganteus) OT; stem often purple; swamps & other moist places; NB to SC & GA ashy s.f. (10.mollis) us. Ozarkian
heads large; petiole long .... Jerusalem artichoke (16.tuberosus) OT; moist soil & waste places nearly throughout the e US

Group V

small wood sunflower (8. microcephalus) OT; woods & brushlands; NJ s.

Group VI

..... stem hairy; narrow lvs stem hairy; wide lvs
..... tall sunflower (17.giganteus) OT; stem often purple; lvs tapering to a narrow base; swamps & other moist places; ME and NB to n SC & n GA divaricate sunflower (3.divaricatus) lvs widest anear the truncate or broadly rounded base; abundant in dry woods & other open places; MA to FL

Group VII

..... stem glabrous; narrow lvs stem glabrous; wide lvs
21)lower lf surface pale, more or less glaucous, only sparsely or not at all hairy pale-leaved sunflower (5.strumosus) stem often with whitish bloom; OT; woods & open places; ME to FL pale-leaved sunflower (5.strumosus)
21) green and generally hairy, not glaucous ..... .....
22) upper surface of lvs us distinctly scabrous; lower surface rather coarsely long-hair (1mm or longer) tall sunflower (17.giganteus) stem often purple; swamps & other moist places; ME to SC & GA .....
22) us scarcely scabrous, the short hairs tending to be more or less appressed; lower surface more finely & shortly hairy than in #17, most or all of the hairs well under 1mm sawtooth sunflower (18.grosseserratus) bottomlands, damp prairies, & other moist places; ME to GA & TX .....
23) invol bracts very loose, evidently surpassing the disk; lvs thin, gen strongly serrate ..... thin-leaved sunflower (6.decapetalus) lvs thin, sharply toothed; OT; woods & along streams; ME to GA
23) invol bracts only moderately loose, sl or not at all surpassing the disk; lvs fairly firm, inconspicuously serrulate or subentire ..... pale-leaved sunflower (5.strumosus)