When you say "portrait lens" to a photographer, usually they're talking about so-called 'longer' lenses. That is, lenses whose focal length is generally in the 85-130mm range (on 35mm cameras at least). You'll read about how longer lenses flatten perspective and are generally more flattering to the subject. On the other end of the spectrum they'll say that wide angle lenses are not to be used for portraiture because they distort or at least exaggerate people's features. Making big noses bigger and that kind of thing.
The thing is, most of this is either misleading or wrong. It's really all a matter of distances, not focal length which causes these effects. Focal length comes into play because it effects your field of view, that's the amount of the scene left to right you capture with it, usually represented by an angle.
So for our discussion, let's imagine that your 5 feet from a friend of yours. To really visualize it, go get a friend and a decent range wide to telephoto zoom lens and try it. Being 5 feet away from them, your perspective of them is about as normal as can be. They're 3 dimensional without looking distorted. If you had a 50mm lens on your camera and took a picture, you'd get pretty much what you're seeing right now. That's why they call 50mm lenses 'normal'. It would probably be a pretty boring waist to head portrait.
Now if you wanted a photo of just their head and shoulders you have two options, either you can zoom your camera up to 85mm or so, or you can 'zoom with your feet' and get closer with the 50mm focal length. If you did both of these you'd see that they look different from each other. But that's not because of the focal length, but rather because you got closer with the 50mm to get the same framing. In fact, if you took your original waist up shot from the last paragraph and cropped it to the same framing as the zoomed in 85mm shot you'd see that they're identical.
So if you want take a head and shoulders shot zoomed out to 28mm or so, you'll notice that you have to get REALLY close to the subject to fill the frame. It's this closeness that causes the distortion of close-up wide-angle portraits. You can even see this without a camera; Just cover one eye and get a few inches from your friend's face, it'll look distorted, just like the 28mm lens.
Ok Bill, so what's your point? Well it's just that any lens can be a portrait lens where the person looks normal and not distorted. It really just depends on how much of their surroundings that you want to include in the picture. Go back to 5 feet away from your friend, look through your camera and zoom in and out and see how the framing changes. Maybe the wood paneling behind and that flower pot next to them are really interesting elements in the composition. If so, maybe shooting wide-angle works, or maybe it's all distracting and so you zoom in and shoot something tighter. Maybe somewhere in between. The point is that it's not about one focal length being 'better' for portraits. They all can be, it's really up to you.
Personally I love more environmental wide-angle portraits. I like seeing and working with the space the subject is in. I think it makes portraits more interesting. You can tell this by looking at my work as well as my lens compliment. 28mm, 35mm, 50mm primes. I recently bought an 85mm traditional 'portrait' lens and when I take pictures with it I feel like it's speaking a different language than me. It obviously got potential as it's painfully sharp, and all the way open at f/1.2 the depth of field is awesomely narrow. It's just going to take a little getting used to, but working outside your comfort zone is always a good exercise. So if you like long lenses, go walk around with something wide this weekend, or the other way around. Either way you'll probably come up with something different than your norm.