Stems and leaves sure remind me of Ulmus (Elm) too. Not sure if it is one of these but I found two Elms listed at the Arbor Day Foundation Website: http://www.arborday.org/trees/...
My neighbor has a huge Chinese Elm in his backyard and the seedlings are constantly popping up all over my yard and in my containers, it's considered an invasive in some areas: http://www.na.fs.fed.us/fhp/in...
~ I'm an old gal who still loves playing in the dirt!
~ Playing in the dirt is my therapy ... and I'm in therapy a lot!