Looks like we have a little spelling inconsistency here.

AMG lists 39 recordings of "Polk Salad Annie," notably by Tony Joe White (the writer) and Elvis Presley

...and only 2 recordings of "Poke Salad Annie"

However, poke salad is made from pokeweed, Phytolacca americana, and every scholarly botanical web site I can find (such as the ones at the University of Florida and Purdue University School of Veterinary Medicine) spells it that way.

(Click here for another nice photo of pokeweed. And, say, it doesn't look much like turnip greens, does it?)

On Google,
"poke salad" -annie gets 742 hits;
"polk salad" -annie gets 414 hits;
"poke weed" gets 830 hits;
"polk weed" gets 29 hits;
pokeweed gets 7,990 hits;
polkweed gets 50 hits.

But I see the poke/polk controversy was already discussed in both of the threads that Spaw linked to.