The native orchids of Florida could use some help. Some of these were used medicinally by the Native Americans, although there is not a large market the way there is for goldenseal.

I think the Gumbo-Limbo tree has some potential. It is well known in Caribbean herbalism, not so well known in modern US herbalism.

Other things to consider include saw palmetto, passionflora. Cerassie is one of the most common herbs used through the Caribbean, not sure if it is a native to Florida.

If a plant is on the threatened/endangered species list, you can't 'interfere' with it in any way without a permit. This includes gathering the seed, leaves, stems, or roots. Even if you are trying to rescue and foster the plant, you need a permit to go beyond passive preservation of habitat.

If you want to give back to mother nature, add something for bees, butterflies or hummingbirds. I have a row of tea plants (Camellia sinensis, used to produce green tea/black tea). At this time of year, there is not much for the bees, but those Camellias are blooming profusely and are covered with busy bees.

I'd start by contacting groups like the Florida Native Plant Society, and looking into other resources through a Google search or via your local library.

In other areas, plants like goldenseal and ginseng have become rare or endangered in the wild because of irresponsible overcollecting, so it's important for herbal enthusiasts to help protecting remaining populations and make sure that the products we buy come from companies that avoid wild harvesting.