There are a ton of different species of mahogany. I would use Merantti. It's a little harder than the normal African Mahogany. I put it in my 1200sf deck and it has held up well for the past 3 years. Do not use a film forming finish like poly or teak "finish". Use a pigmented penetrating oil. You want something that you can lay over the previous finish and not have to strip. I use ReddiSeal.