All seedlings will grow at different rates, this I understand, but have you ever seen a seedling with such TINY leaves? Normally I would think they would keep growing, but they are already completely open and they've been this size for several days now - our current temps are in the upper 60s with 50s overnight. (Ignore the label please, it's wrong and I haven't changed it yet; this is a seedling from Seiryu, collected 2014, as are the two beside it in the second picture.)
Hi Andrea, I get a few seedlings that do this. Sad to say that they usually die, and when I check the root is undeveloped. I put it down to "failure to thrive", which is just a catch all for "failed". Of course there are some seedlings with very small leaves, so maybe you have one of those. I had a batch from "Lima Gold" (from Ed Shinn's garden that he very kindly sent me) with many small leaved seedlings. I've given most away but kept a couple, after 6 years they are perhaps 30cm high, leaves are <1cm. They're neat little maples though not worth naming I don't think. Glad you're getting some nice weather! cheers, -E