Callaloo? Calaloo? Calalloo? Those L's seem to travel about and multiply at will, but the signified does not. Callaloo is a leafy green vegetable commonly used in Caribbean cooking and also a Caribbean stew made with the leaves.
Callaloo are the leaves of any variety of taro plant and are also called dasheen leaves; though one source (www.foodsubs.com) says that the leaves of taro, like the roots, contain the toxin calcium oxalate and so must be cooked for 45 minutes before it can be eaten, no other sources mention this, and since I've never cooked with callaloo I can't confirm this. Any kind of bitter green can be substituted for callaloo: spinach, chard, collard greens, sorrel, etc. Callaloo leaves are apparently much larger than these other greens - over a foot long, says that same source - so must be chopped before being used.
The stew or soup is a kind of gumbo, a melange of ingredients and flavours prepared in different ways throughout the Caribbean islands. The greens are the core of the recipe, and other common additions are okra as a thickening agent, tomatoes, crabmeat or lobster, and bacon or ham. The stew is liberally seasoned with garlic, scallions, thyme, and scotch bonnet peppers, which are really hot, so the stew is very spicy and sometimes called pepperpot. It all sounds great, but I've never eaten or cooked this, so I can't give you a recipe. The one above seems a fairly standard, from what I've seen, except for the ackees and lack of meat.
www.b-v-i.com/Cooking/Callaloo/default.htm has a good general description of the dish, and advocates experimenting, which is where I'd start if I was going to make this.