The Plant and Fungi Kingdoms evolve on land so closely together in time that we are unclear which of the two came first. The Fungal Fusion hypothesis opts for neither, suggesting a joint venture. It proposes that fungi and landward photosynthetic algal symbionts joined together to evolve the capability to survive dryness. Was it just a joint venture or did it go further?
Perhaps land plants arose through both a somatic (body) and a permanent fusion of fungi with algae. This symbiogenesis is much like the "horizontal" gene transfer which bacteria practice.
Life on land poses far different demands than did life in the sea. Life forms develop "hypersea"— the movement of sea water onto land, but inside organisms.