Good Morning John, 

Thank you for contacting the U of M Extension Service. 

Please click on the following link from the U of M about catalpa trees: https://campustrees.umn.edu/catalpa

Here is another link to the USDA Plant Database about Northern Catalpa: https://plants.usda.gov/plant-profile/CASP8

If you scroll down, you can download a fact sheet about the tree and a plant guide. 

This information states: 

Twigs in winter have a unique identifying characteristic. They have sunken leaf scars which resemble suction cups. Their whorled arrangement of 3 scars per node is another trait easily identified.

The above should give you all the information you want about catalpa. 

Good Luck!