What is this plant producing blacks seeds in a calyx like a Physalis but isn't one?

Question

I found seeds on the street on a windy day in February and believed it to be a physalis. Having sown them and seeing the seedlings now, I'm sure it isn't what I expected, but what is it?

I was thinking in the first place that is a Physalis peruviana because the seeds were inside a papery, light brown calyx. The seeds were black with the size of a pea (4mm in diameter). Later on I saw real physalis seeds and cracked one of my seeds open to see whether there are smaller once inside or not. Not the case.

I planted them 6 week ago. I'm now confronted with one plant per seed. Produced leaves are brown-reddish in the beginning and then turn green and resemble oak-leaves in some way . The stem makes me guess that will become a wooden plant - a tree or a shrub.

Here a picture of the seedling:

Answer 1

Well, it is asking the question which makes me find the answer, recently. It is, most likely, a Koelreuteria paniculata, also known as goldenrain tree.

I didn't remember, but now I do: there were several black seeds inside the seed pot - as described by wikipedia, 3 of them. The images there fit exactly to what I found on the street. However, I'm not in Asia. I need to check where the tree(s) is - in Paris, France.

It was my assumption about tree or shrub, which made me search for it in a different way.