On first examination I just presumed they were weeds that had taken up residence in the pots, yet due to the concentration and similarity of each seedling it got me wondering. So I decided to ask the opinions of the other WeeTrees forum members and post my pics. The resounding response I got was they could be Japanese Maple but its far too early to tell as most seedlings look similar at first. So I left them growing for a few more weeks to see what happened and to my joy the second pairs of leaves emerged and were unmistakably Japanese Maple. The seedlings have now been transplanted into individual pots and are doing very well.
An interesting point that can be seen is in the variation of leaf type between the seedlings, some have more dissected leaves than others. Although all seeds were from one mother plant, each seed has the chance to develop into a completely new form of that variety, so seeds can offer an exciting variety. I think the thing I learnt most from this was that nature will do what it wants, it will grow whenever and where ever it wants to and very rarely where you think or want it to. I may have been quick to dismiss the seeds after the first season but I gave them more time and have been rewarded for that. So I now have 12 seedlings which I will keep a record of and update their development on here.