The Munching of the Green!

It's Saint Patrick's Day, a holiday that will be celebrated in many cities around the world where there's a considerable number of Irish. In Belgrade there's an Irish Pub, and I've heard they've planned festivities for the beer-drinking crowd, though few Serbs know who Saint Patrick was. Spring still hasn't shown us much green, so I decided to go out and buy myself some. Pictured above are two kinds of greens I like a lot. The long, thin ones are called zelje (ZELL-yeh) and are often used to wrap around seasoned meat and rice, then covered with a broth and baked. Serve with thick yogurt! The smaller leaves will actually grow much larger (not these; I ate them), and are usually cooked/steamed and served with sour cream and garlic. They're called blitve (BLEET-veh). I think they're called collards in English, and I honestly don't know what zelje are. I've Googled, but nothing looks quite right. Help?