Question
My husband brought me a seed pod from a tree that he had never seen before and was quite fascinated by.  I know I've seen them before but never knew what the name was.  We live in MO, near St. Louis.  The seed pod looks like a huge overgrown string bean.  It was approx 18 inches long, green and growing in clusters/clumps.  I have no idea the leaves or bark.  This was either lay May or early June.

Answer
Sounds like northern catalpa, Catalpa speciosa.  Leaf: Whorled (or opposite, when whorled one of the three leaves is often smaller), cordate, 5 to 12 inches long, pinnately veined, entire margins, overall soft and flexible feeling, light green to green above and soft pubescence on the underside.
Flower: Monoecious; very showy, white (yellow and purple spots on insides), 5 fuzzed petals form an overall bell shape, 1 inch long; appear in open, branched, upright terminal cluster (8 to 12 inches long) in late spring.
Fruit: Long (10 to 18 inches) bean-like, hanging capsules, round in cross section, very stiff; each capsule contains numerous flattened seeds with 2-papery, fringed wings; the seeds mature in autumn, but the capsule may remain attached over winter.
Twig: Stout, green, and later reddish brown in color, numerous lighter lenticels; terminal bud is absent, lateral buds are small and covered with red-brown scales; leaf scars very unique elliptical or round sunken saucers, light in color.
Bark: Gray to reddish brown, separated into irregular shallow fissures and scaly ridges.
Form: A medium sized tree to 80 feet with spreading, crooked branches and an irregular crown. The bole may be straight but is generally crooked.  


Here is a web link to pictures of this tree. http://www.cas.vanderbilt.edu/bioimages/species/casp8.htm