i don't know, this strange plant appeared in one of my pots - possibly it was a dormant seed in the peat moss - any ideas
I think it would depend on the origin of your peat moss, if it is in fact from actual sphagnum peat, if it came in a sealed package, or from a huge pile open to a plant nursery, or was shipped in from another continent (actually likely). I don't know that there is any way for you to know for certain where it originated. So let's assume that it was a seed from something in your area, perhaps from the nursery, or from random blowing seeds. Not square stems, so not a mint. Not especially pretty so it either has herbal interest, great flowers, or is a common weed. How aromatic are the leaves? Pinch a bit of a lower fading leaf and sniff. Lantana camara comes to mind, but I'm thinking the leaves look a bit too soft for that.
The peat moss comes from the Baltic - it is a sealed package (around 50 kg) - I do not use local nursery peat moss. The leaves are not soft.
I considered Urtica dioica initially, since I have experienced it first hand, so to speak. Also the other hand and my left shin where I knelt down to get a closer look at it. Only time I've seen it here in thirty years, although we have other stinging plants. This doesn't look like my childhood memory of it, but then I have been wrong about it before. "Hmm, what's this? It looks like stinging nettle, but it can't be. Better roll in it to be sure..." Lantana camara has these little tiny almost thornlike structures on the stem and I think sometimes under the leaves that are surprising and could scratch you if you grab and pull forcefully. I don't see them on the pics, not even #3. Those rough hairs on the stem in that pic would just be a bit rough if it is a Lantana sp.
