Helianthus annus 
f. lenticularis

Showy Sunflower

Receptacle Flat or Slightly Convex
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

receptacle flat or nearly so

disk purple or dark brown

scales between disk florets not very hairy

 

Helianthus Characteristics

receptacle flat or convex, not conic or columnar

receptacle with chaffy scales between the florets

flower heads with both tubular and ray florets

rays conspicuous

ray florets yellow