My petunias got a fair amount of comment when I posted a quick snapshot of the greenhouse full of them on bloom day, so I decided to scan, Ellis Hollow-style, some of the flowers so you can see more of what they look like.
First, at top left we have Petunia integrifolia (small, magenta, no scent) and at top right P. axillaris (large, white, extremely fragrant). Below are a selection of some of their grandchildren (aka: F2 generation) many of which are fragrant though are not. This is actually the hybrid that started it all back in the 1800s -- modern petunias are derived from the hybridization of these two species, with a lot more colors added, and most of the fragrance lost.
Next: At top left P. exserta (red, unscented), and at top right, P. axillaris again and below them, their grandchildren. P. exserta is a cool species because it is the only red, hummingbird pollinated petunia -- and it is nearly extinct. It was only discovered recently, and is only known in the wild in one tiny population of only about a dozen plants. Luckily, seeds have been collected and distributed, so these unique petunia can be preserved in greenhouses and gardens around the world. I like the clear pink colors of this hybrids a lot better than the magenta tones of the first... sadly, only a very few of them are scented.
P. axillaris and P. integrifolia. As far as I know, P. exserta is not commercially available, but if you want some, shoot me an e-mail (engeizuki at gmail dot com) and I can send you some. (UPDATE 7/6/2011: I am out of seed to share with people, however, I did send some seed to Annie's Annuals, and you can buy plants from.) It is an easy, self-sowing annual for me, and the hummingbirds love it.
And, if you are intrigued by the hybrids you can create them as well! It is SUPER easy: Step one: Take P. axillaris flower. Step two: Shove it into a P. integrifolia flower. Step three: harvest your hybrid seeds. Then you get the fun of growing up all the different types and picking your favorites to save seed from for next year, creating your own, unique strain of petunias.