One way to identify the native catalpas
The catalpa trees have bloomed recently in Christian County, Kentucky. I don't know if the catalpa in these photos is a southern catalpa (Catalpa bigenoides) or a northern catalpa (Catalpa speciosa). The northern catalpa is sometimes called a hardy catalpa. It is found in USDA Zones 4-8, whereas the southern catalpa prefers Zones 5-9.
I might have made a guess about the identity of this catalpa if I had looked closely at its blossoms. The northern catalpa's blossom is supposed to be more thickly spotted on the inside, but how would you know without a southern catalpa blossom to compare it with?
According to tree expert William H. Lamb, writing for the American Society of American Foresters in 1912, a reliable clue to identification can be found within the catalpa bean. The long, thin pod of the catalpa (up to 18 or 20 inches in length) contains a septum or partition along which the beans are arranged. If the septum is flat and thin, the tree is a southern catalpa. If the septum is round, the tree is a northern catalpa. The advantage of this identifier is that one doesn't need to compare specimens from both catalpas.
Being able to distinguish between the two catalpas was important to foresters in 1912. Though catalpa wood is soft, it was a favored wood for railroad ties and fence posts because it is durable in contact with soil.
Northern catalpa wood was harder than southern catalpa wood, and thus superior for railroad ties, particularly as trains grew heavier. Farmers wanted to grow and harvest northern catalpas, selling the largest part of the trunk for railroad ties and smaller parts for fence posts. Some railroads even had plantations of northern catalpa.
In addition, the hardy catalpa was considered a good candidate for the treeless American prairies. Though it prefers a moist situation, the hardy catalpa can endure dry conditions and cold winters. I can vouch for this myself. Two big catalpa trees grow in the sandy, often arid. front yard of my brother's ranch in Kansas.
I'm rather fond of catalpas, but that may be because I've never had one. In favorable locations, they can be so prolific that they're considered invasive. They're also a rather messy tree, when those big leaves and pods drop.
Furthermore, the catalpas aren't even listed in the bible of wildlife value -- Martin, Zim, and Nelson's American Wildlife and Plants. When this book was published in 1951, apparently no report had been made of an animal eating any part of a catalpa tree, anywhere in the U.S., ever.