Helianthus annus 
f. lenticularis

Showy Sunflower

Regina 
02-Sep-2002

The cultivated sunflower (Helianthus annus var. giganteus) has flower heads 15 to 30 cm across.

I have found that neither Budd's Flora nor Flora of Alberta easily distinguishes between Helianthus and Rudbeckia (Rudbeckia hirta is Black-eyed Susan) in their keys.  However, they do note that the receptacles of Rudbeckia are more conic.

Annus Characteristics

pubescence rough

involucral bracts abruptly attenuate, with conspicuous marginal hairs

receptacle flat or nearly so

 

Helianthus Characteristics

involucre not glandular nor glutinous

involucre bracts in one or more series, but all of the same nature

receptacle flat or convex, not conic or columnar

rays conspicuous

ray florets yellow