As landlubbers, we often let ourselves think that if salty seawater is undrinkable for us, it could be even worse for plants. However, certain types of angiosperms have found ways to not only thrive on marine environments but specialize on them. These are the mangroves and four families of alismataleans collectively called "seagrasses".
But what about the other major groups of plants--the conifers, the ginkgoes, the ferns, the cycads, the liverworts, the mosses, the clubmosses? In an alternate Earth, could any of them have what it takes to adapt for saltwater life and grow into marine forests as complex if not more so than the kelp forests of back home?