I can normally figure these out on my on but this one has me stumped. In one of our plots in northwest Nebraska. Looks like a chicory or a dandellion of some sort. I know I've seen it before but can't think of what it is. Never been in this plot before. Plot was planted in rye from a local source and arrowleaf clover.
I'm going to say wild lettuce (Lactuca serriola). It could also be the native version (Lactuca Canadensis). I can't tell them apart when they are that small.
Check out the link below and click on the little picture on the right side to enlarge it.