JS, these things can be tricky. Much depends on time of year when the flooding occurs.

I've seen plenty of white pine and white spruce growing in sites that tended towards the wet side. But this is in northern Wisconsin, quite far removed from your situation. Nevertheless, I'd try those two and perhaps the Norway spruce. Thuja is a possibility, as 'cedar swamps' are common in my neck of the woods. Even here, though, plants grown in a nice well-drained nursery field will not necessarily like being moved into a puddle.

Though you want evergreen, I'd definitely use some Larix if it was my project, provided the site is full-sun.

+oM

There are very few conifers that will take flooding in warm climates, and the ones that do (Taxodium, Metasequoia) are deciduous. One that is evergreen and would be worth trying is Chamaecyparis thyoides (White Cypress), but it is slow-growing.

Larix, although tolerant of wet conditions in the taiga, isn't so in warmer regions, and will need good drainage in MO.

Resin

it funny you should ask because I`m looking for the same thing and I live in a similiar climate. Evergreens are more difficult in my area now due to the government reintroducing deer. They can completely anniliate young evergreens. I have totally given up on white pines for that simple reason. White cedar aren`t tolerant of my regions drought. I like bald cypress, pond cypress,and dawn redwood. So far I haven`t had much luck with larches, but I`m not one to give up. Loblolly pine does pretty well. It tolerates extremely dry soils, wet ones and even the ones where no other pine here will live because of poor clay soil. There are better pines for less troublesome sites. It also has some problems with insects. I`m getting ready to post on just where I can locate just a few. So far all I have found is where I have to buy a thousand. Where they are native they aren`t sold much anymore due to insect problems. Maybe the problems aren`t as severe here. In an extremely cold winter they do suffer from wind-burn in my region but they always seem to recover.

Resin may be correct with his Larix comments, but there are numerous bogs with American larch as dominant species as far south as SE Wisconsin-an area that certainly has hot, humid summers. But yeah, you want non-deciduous.

+oM

Black spruce.

Siberian strain of the swiss stone pine, although tends to be rather slow growing.

Pitch-loblolly pine seems to have hybrid vigor & should have good genetics for tolerance to wet soil -- Pitch pine grows in Jersey swamps. Arborvitaes in general have some tolerance too.

Norway spruce: no problems if in spring time. In our conditions (Europe, Lithuania, zone 5 and 6) it is quite common. But "periodic saturation (maybe a week or so for each overflow occurance)" - smth new and tricky. Don't think somebody have tried such environment :)

Have seen Loblolly pines growing in areas that flood periodically in north Louisisana. What I observed there was that if the tree grew up from a sapling in wet/flooding area, it would survive and thrive. IF the tree was already grown and then was subjected to periodic flooding (say shallow area of a man-made pond), the tree would almost certainly die.
Shortleaf pine will easily grow on clay, and areas that get wet, but I don't remember ever seeing it in an area that routinely floods. Same is true for eastern red cedar.
Have no experience with the rest of trees you mentioned.

Very old thread, but I think Sciadopytis verticillata is worth a mention. Some references give it good tolerance of wet soil, but most tend to give the old “moist but well drained” thing. I did read that it used to be part of the Taxodium family, which might explain its tolerance. I’d like to hear someone else’s ideas about this.