Not actually a field sketch, as I brought this one leaf in the house for closer examination.  It was evening when I got around to doing a couple drawings of the distinctive characteristic of an elm leaf. This was a dry fall leaf.   We used to climb the elms as kids in SW Nebraska. The leaves also have a very distinct feel to them; and very distinct parallel veins as well. One side of the base may have 2 or 3 more veins than the other side.