New England and Manhattan are the two most popular varieties, and despite the numerous recipes for both kinds of clam chowder, you can easily tell the difference by looking and by tasting.
New England Clam Chowder
New England Clam Chowder is cream-based. In addition to clams, the soup often contains potatoes as a thickener and is commonly seasoned with fresh thyme, salt and pepper.
Manhattan Clam Chowder
Manhattan Clam Chowder is a water-based soup with tomatoes added to the broth. In addition to clams and tomatoes, common ingredients include onion and celery, and the soup is often seasoned with salt, pepper and parsley.
When the French settled the Canadian Maritimes between the 16th and 18th centuries, they made soups out of the local seafood, according to "The Oxford Companion to Food."
In "50 Chowders: One Pot Meals--Clam, Corn & Beyond" Jasper White writes that in 1894 Charles Ranhoffer, the chef of New York's Delmonico's Restaurant, published a recipe for a tomato-based clam chowder in his cookbook "The Epicurean."