Odd, I'd never heard of Swietenia mahagoni until now. The reference book I mostly use (Tropical Timbers of the World) doesn't have it listed. Another reference says that Swietenia macrophylla is sometimes called Cuban mahogany, and it does grow in Cuba. A search on the net found it though, so Nick and Terence are right.
I just looked it up in my books. Two (The Wood Book and Woods of the World) don't list it, and one (Cabinetmaking Timbers, published 1933) does. Odd.