I tried replying earlier, but a user error occurred (clicking X on the wrong tab) and I didn't want to type it all out again. In the meantime I took a couple of pictures. What I found surprised me and now I am glad I didn't get that reply made.
I had forgot to mention the leaf size in my original post. The largest ones are 1/2 inch long.
Here are today's pictures.
Underside of the leaves
The stem. Now this is what surprised me... I can see thorns/prickles. They are very soft because I still could not feel them when I rubbed my fingers along the stem.
We now have a red raspberry bush, we got it this spring and it already bore fruit. Would any seeds from the berries germinate already? The undersides of the raspberry are almost white. I cannot remember their texture though. I am learning that in some cases seedlings often do not resemble the mature plant at all, so this could be a raspberry.
