Ferns can grow taller than mosses because ferns are vascular plants and mosses are non-vascular. Most plants are vascular, which means they have a system of vessels that transport water and nutrients throughout the plant. For this reason, vascular plants can grow very tall; their vascular tissue moves needed molecules, such as water, all the way to the top of the plant or tree. Mosses, by contrast, are lacking this internal transport system and therefore cannot grow to be tall. They must rely on absorbing moisture directly from their environment and so must remain low to the ground where water is accessible. Mosses must live in moist, damp environments for this reason. Ferns are also found in shady, damp areas because like mosses, they use spores as their method of reproduction. Spores travel through water to unite and reproduce
