Heliopsis helianthoides
A plant that does indeed resemble Helianthus. My pictures are from Indiana, where it is a common plant in low, wet areas. I haven't yet seen it in the southwest, though it does occur here.
A pseudanthium near Griffy Lake on the north side of Bloomington, IN, 8/11/03.
Plant habit near Griffy Lake, 8/11/03.
A cauline leaf near Griffy Lake, 8/11/03.
A ligulate flower near Griffy Lake, 8/11/03. This genus has fertile ligulate flowers, whereas Helianthus does not.