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.

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Annus Characteristics
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pubescence rough

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receptacle flat or nearly so

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disk purple or dark brown

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scales between disk florets not very hairy

 

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Helianthus Characteristics
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receptacle flat or convex, not conic or columnar

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receptacle with chaffy scales between the florets

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flower heads with both tubular and ray florets

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rays conspicuous

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ray florets yellow