Can they go together in the same plot? Will one choke the other out over time? I thought the contrasting yellow/purple flowers would look good and am thinking about ordering them. Just wondered if anybody had any experience ...

in my zone, they go dormant during the winter. that said, they are consistently perennial. just don't make the mistake of thinking that they need no water -- they need SOME. i've seen very effective plantings of them in hard to water areas, like islands in parking lots. home depot sells trays of 9 plants for $12. those nine plants could easily cover a large (say, 20x20) area in a season. they are very easy to propagate. i've forgotten the name of the kind woman who gave me a garbage bag full of cuttings at a trade last year in orlando. but nearly all the cuttings took root. i used them as a green manure crop in an area that now is a veg garden. i still get sprouts coming up, even after i dumped dozens of bags of leaves and compost in the area on top. i've seen them at ECHO as a groundcover under fruit trees. it looked smashing... Here is a link that might be useful: perennial peanut @ echo

Where's your sense of adventure. Go ahead and pull over the side of the road, where it's safe to do so of course, and take a clump of it and propagate it.

I never thought of this, but my wife asked would someone who is allergic to peanuts have the same reaction to Perennial Peanut, since they are related.