Watching the experts constantly renaming groups and changing categories will give you some sense of how hard it is to place the thousands of orchids into groupings that make sense. It's often not too difficult to tell that a plant is a cattleya by looking at the plant itself. In general cattleyas are sympodial orchids with thick creeping rhizomes (almost like a vine) sending up stems, from the leading point of the rhizome, that swell into water storing psuedobulbs and narrow again where the leaf attaches. They generally protect the buds with a papery sheath. Many of the flowers look like, what we think of as, classic cattleyas but it's not always possible to tell from the flower if it's in the cattleya alliance or not. I think the rhizomes and the pseudobulbs are the best indicators of the alliance but, then again, there are always exceptions.