Now that it's Fall you'll probably see this thing in flower shops -it's marketed as 'Pumpkin on a Stick" It's not a pumpkin at all nor is it closely related, it's Solanum aethiopicum, also known as the Ethiopian nightshade. Is it invasive? Is it poisonous? Where did it come from?
It is not on the USDA's invasive plant list, it is not listed as poisonous and is widely eaten in Africa where it is native, but always use caution with anything in the genus Solanum (for some real unnecessary alarm read here about a poisoning involving a different Solanum species). That being said it can be grown from seed and can get 8 feet tall. It takes 70+ days to fruit so you should plant it in the first week of August to get fruit by Halloween.