I,too, have only had store artichokes. ..donno why !
I wanna know too.

Hmm, this question has been floating unanswered for a while. I'm not an artichoke expert, but maybe I can begin an answer. Yes, there are different types. Two main types are the Green Globe type and the other is the Imperial Star type. They do have distinctive, but slight differences in shape. I'm not sure about the heart size being related to type, though. It could be, or it could just be natural variation in the plants. Artichokes don't seem to have undergone the same intensive breeding as some other vegetables, or maybe they just don't lend themselves very well to standardization. When you buy artichoke seed, there is great variation in whether the seeds germinate and if they do, how they grow. And another thought is that maybe the ones with bigger hearts just had better fertility and water during growth.

So, I don't know the answer to your whole question, but there's a bit of what I do know and a couple of guesses. Cheers!

Thank you. Maybe if I email a seed company they'd know. If they do I'll post the answer.