From Jay:
The foliage purchase menu is already sorted by habitat. Those that cannot be in exhibits will be at the end. Aquatic will be immediately before those. Those that can be in any exhibit will be immediately before Aquatic, with "Many" as the habitat. For foliage made for a specific habitat, ZT's and some user foliage will have a specific background on the purchase menu icon to match the habitat.
As for adding to the purchase menu filters for personal use, "My Favorites" is reserved for that. The "Combined Menu Filter Names" download topic mentions that and how to use it.