The pumpkin isn't a vegetable. Not only is it a fruit, botanically, it's actually a berry. But it's the only berry that has a hard outer shell. Pumpkins belong to the same family as cucumbers, melons, spaghetti squash, and gourds. The true big orange pumpkin (Cucurbita pepo) needs a long growing season but no early-summer heat, so it won't grow everywhere in the US. That's the reason three other species - technically winter squash but big and orange - are grown as pumpkins. One of the oldest pumpkins in North and South America is called the Cheese pumpkinbecause it resembles a wheel of cheese. There's a white pumpkin named Lumina, and a blue, drum-shaped one known as Queensland.
Source: 'The Perfect Pumpkin,' by Gail Damerow