 The leaf is very coarsely toothed, the teeth are curved and gland tipped, and the petiole is flat; they are dark green in the summer and turn yellow in the fall (but many cottonwoods in dry locations drop their leaves early from the combination of drought and leaf rust, making their fall color dull or absent).Due to the flat stem of the leaf, the leaf has the tendency to shake from even the slightest breeze.This is one of the identifying characteristics.