Original construction was all teak. It's availability has absolutely plummeted and as such price has skyrocketed, and it's tough to tell if you're getting the South American version or the African version during purchase. Most new teak now is from plantations and is young wood which means it's mostly light colored, wide grained, weaker sapwood from mid-sized trees that are encouraged to grow at the fastest rate possible. It has the same weather resistance, but it structurally and aesthetically deficient compared to old-growth or heartwood. It's REAL hard to fine heartwood in anything other than salvaged timbers nowadays (which command an absolute fortune unless they're beyond salvation). Teak by it's simple biology contains a very weather resistant oil which made it ideal for marine uses b/c it won't rot. It discolors, but a little sanding can bring back ALL the original luster, and it's typically left un-varnished; teak oil is the only treatment used in most marine applications. Mahogany has nowhere near the overall weather resistance, but is significantly cheaper and, with a nice sanding and finish coat, is absolutely GORGEOUS. Generally, teak was always used for exterior flooring and trim work, and mahogany was always used for interior finish carpentry or cabinetry b/c it's much easier to cut/shape. My father has been a woodworker his whole life so that's where I get most of my relatively limited knowledge, but our member Palmetto does custom work for our members and can probably give you some more GREAT info.
My two cents - if you can find REAL teak, and have the ability to have it machined, it's the ONLY way to go for the exterior trim...but be prepared to fork over your first-born. Mahogany, Ipe, African teak, and a few others make quality substitutes if availability or price are your limiting factors.
