There are a lot of species that occur in OK. You might go here

http://www.oklahomaplantdatabase.org/

and type Asclepias for you search term and then select your county to narrow it down. Which species you use will depend on your soil conditions. By clicking on some of the records you can see the habitat where the plant was collected. For example, one of the records of A. speciosa says "Disturbed roadside, level plain, compacted clay loam, grassland", which suggests medium moisture and tolerance for some clay. One for A. incarnata says "Wet pond bed and pond bank, level slope exposure, clay loam" which makes sense since that species is not tolerant of dry soil and will grow quite happily standing in water.

I've grown A. incarnata in several different areas, and it can tolerate quite a lot of drought. It may prefer moist conditions, but it has done fine in my sunny, sandy soil with rare supplemental irrigation.

Martha