Rich,
When I get areas with plant stains, they are either from a water stain or a mold stain. The mold stain is darker and less rustlike. If you’re talking about water stain I use our regular 101 with a big shot of orange deodorizer in it. Let this dwell for 10 minutes or more and flush out with our cleaner and Upholstery Mate (repeat if necessary). Buff or dry the area as much as possible after this procedure. I get water stain out better than 95% of the time.
If you are dealing with mold stain, I have not found a good way to remove that. Also, sometimes plants are in wicker baskets. These create a wood stain, and we both know that we don’t have much success with wood stains.