I thought of Winged Elm right away too, porkpal. I'm sure that's what the tree is, and those vertical extensions on the trunk and branches are the natural way the bark grows. They are really neat trees.
But there is some rusty fungus on the undersides of the leaves. If this is what's worrying you, it's probably not anything serious. The trees will lose their leaves in September or October, and to keep from carrying the rust over to next spring, just be sure to rake up and remove the leaves. Don't compost them or the fungus will hang around in your yard and infect the leaves again next year.
If you want to slow down the spread right away, just remove any leaves you can reach that have a lot of it. Bag them up and put in the trash - again, if you compost them or use as mulch, the fungus will fly around some more. Also when you're watering, try to always water in the mornings, so that the leaves will dry out during the day. Leaving water on the leaves at night encourages fungal growth and spread. It's better for the plants to water in the morning anyway. They get a good drink before the heat of the day sets in, and less water evaporates in the cooler air, too.
