https://www.inaturalist.org/projects/lichens-of-florida/journal/74081-common-inat-suggested-identification-problems

If you want the best way to tell them apart, find some with emersed grown stems and take a picture of the joint on those (as it can be hard to see on submersed growth). If the auricle (the little flap at the crease of the joint) is there, then it’s regular N. officinale. But if it’s totally smooth, it’s N. floridanum!