This section is from the book "Who's Who Among The Wild Flowers", by W. I. Beecroft. Also available from Amazon: A Field Guide to Edible Wild Plants.
Tall Lettuce: Wild Opium: Horse-weed. Lactuca canadensis.
Composite Family. June - Sept.
Found in roadsides, borders of fields, thickets, moist soil. Canada to Georgia, west to Arkansas.
Pale-yellow, numerous, small, in loose, spreading cluster terminating stem, 4 - 10 feet high.
Lower leaves deeply toothed, often 1 foot long, narrowed toward the base; upper leaves lance-shaped, toothless.

Wild Lettuce.
 
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