I recommend Sapele.

It looks almost identical to mahogany, but it's less expensive.

In my experience, mahogany and related woods are pretty soft when unfinished. A good varnish is what makes the surface durable. Traditional varnish impregnates the porous surface of the wood with resins, which polymerize into a hard film. Additional coats build on the surface, thickening the film into a protective shell.

I would argue that the finish is more important than the choice of wood, for the value you want to achieve in this particular application.

Here is a link that might be useful: Sapele images.

"In my experience, mahogany and related woods are pretty soft when unfinished"

You've clearly never tried to cut mahogany. It's like trying to cut a rock.

I have stained alder trim in my house. I don't have any issue with the hardiness of it. It still looks great.

Thanks guys. That sapele does look nice! Joe, do you have any of the alder where it gets a lot of contact with people and their things? I like how my current trim can be hit hard with a remote control truck and still be the same. (I still do not approve of that, of course!)

I don't know much about mahogany and have only dealt with veneers prior to this place, but the particular stuff used in this house is really hard. I think it has been shellacked, both literally and figuratively.

I wish they had used it on the floor. Now THAT would be fabulous!

Let me clarify my experience for the less educated commenters.

In my experience, many different species of wood are sold with the word "Mahogany" in the name.

The "true mahogany" comes from genus Swietenia, and has about 3 species that are sold as "Honduran Mahogany" Janka hardness is about 800. That is not a very hard wood. Cherry, Oak, Walnut, and Maple are all harder than true mahogany.

Trees of the Khaya and Afzelia genus are sold as "African Mahogany" This is the same hardness as true mahogany, pretty soft.

There is a common Eucalyptus sold by the name of "Red Mahogany" This is much harder at over 2,000 Janka. But it is not Mahogany or even related to it in any way.

Myroxylon is sold by the name "Santos Mahogany" This is also very hard, over 2,000 Janka. Again, this is not Mahogany.

Then there is this awful junk sold by the various names "meranti" "luan", and "philippine mahogany". It is the hardness of Balsa wood.

I have a good deal of experience making things out of all the above mentioned kinds of wood. I've also done plenty of finish work with Alder (Janka 590) and Sapele (Janka 1510). I recommend Sapele for your application.

The common application where I would use Alder is for a rustic kind of finish. It looks good with a distressed or antiqued kind of finish. I do not think Alder is a good choice for your project.

While I have alder as trim in my house, and it wears great, it doesn't look at all like mahogany. I wouldn't restrict it to a rustic look though. I agree with others that sapele would be a better choice.