This is a "volunteer"; I'm wondering if it's a little mountain ash tree starting up. We live in the countryside and I don't actually see any mountain ash near by. It has 5jagged leaflets on each stem.
Pic isn't quite clear enough - are the leaves alternate or opposite? If opposite, not sure, it doesn't look quite right for an ash seedling, perhaps an elder; if alternate, it could be a rowan.
I don't know what you mean by "alternate or opposite". Also, I realize, there are 7 leaflets on the newer branches, not 5. Is it common for them to have fewer on the first ones?
Opposite means two leaves coming off the main stem together, opposite each other on the stem. Alternate means one leaf on one side of the stem, then a gap before the next leaf on the other side, and so on. Yes; seedlings of plants with pinnate leaves commonly have fewer leaflets on the first few leaves.
