Some type of brassica. I'd guess broccoli.

If it's broccoli keep an eye on the center swirl of new leafs, a tiny forming head should peek out soon. It is a bit late for broccoli so it might indeed be collards.

Collards would be my guess just from the photo but that depends on the variety too as they have several different appearances. A taste of the leaves should give you the answer assuming you know what each tastes like.

Dave

Just judging from the growth pattern I'd also say it's collards. Broccoli could be a possibility as well, but depends on whether it forms a head or not I suppose.