Probably not Zizia aurea seedlings

After putting my stratified native seeds under the grow lights, I was thrilled to see a lush crop of seedings of Zizia aurea (golden Alexanders, zizia d'oré) springing up in only a couple of days. Now that they are getting true leaves, however, they look suspiciously to me like Oxalis (wood sorrel, oxalide). I discovered a nifty resource, Central Region Seedling ID Guide for Native Prairie Plants (PDF), published by USDA, which seems to confirm that these are not Zizia aurea.

I'm going to keep them around a bit longer; maybe they'll look different with age, or maybe more seedlings will come up later? I'm not expecting much though. What a disappointment.