Can someone identify this plant?
As @dd3 stated, it's a spiny (or prickly) sow thistle. It's an annual common in most of the US.

The leaf itself does not have a stem, and if you break the central stalk, it should be hollow and there should be a milky exudate. The plant spreads by fluffy seeds produced from a small dandelion-like flower.

If you pick it while young, it won't hurt (as much); if you prevent it from flowering, it should not spread, although unsprouted seeds can sprout still for a few years (it can come in on the wind as well.)



Prickly Sowthistle