Helianthus annus 
f. lenticularis

Showy Sunflower

Upper Leaf Bottom
Regina 
02-Sep-2002

Budd's Flora keys genus Helianthus as "plants with entire, undivided leaves".  The leaves are, indeed, undivided, but many leaves of Helianthus annus are toothed.

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Annus Characteristics
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pubescence rough

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leaves commonly ovate

 

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Helianthus Characteristics
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leaves not compound

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leaves not linear