Why are there no tree ferns now? How are mosses different from algae? What are rhizoids? Why can’t you call them roots?

Answer 1: tree ferns existed when the planet was with the warmest climate. After a drought they could not adapt, but gymnosperms could.
2 answer: The structure and level of development. Namely: algae is a solid thallus with rhizoids, and mosses are a higher plant with leaves, etc. Mosses are exceptionally multicellular, but algae are not.
Answer 3: Risoids are special organs that help algae to attach to rocks, the bottom.
Answer 4: Rhizoids only help to catch on the surface. They don’t help collect minerals or anything like that.