Coreopsis tinctoria perhaps.

That one is very common in southern Arkansas, and is usually growing in shallow water - creek flats, pond and lake margins, etc.

Here it is, but can't get the focus quite right -- clicking on the pic(s) seems to give a slightly better quality pic. That's one stem, and the stuff to the left is another of the same-type plant -- that one is ~6 ft tall: Your suggestion of Teucrium canadense for the second plant looks to be correct. Thanks. Might have to resubmit a pic of the first plant after it flowers...

when i.d.ing wildflowers it's important to know what part of the country the plant is growing in. It looks like something in Apiaceae, but a location would help nail it.