Mosses: A plant that has no flowers and grows as small leafy stems in patches like cushions clinging to rocks, bark, or the damp ground.
Lichen: A plant-like organism made up of algae and fungus growing together. The algae produces food from the sun via photosynthesis, while the fungus absorbs moisture and provides the protective framework structure for the algae.
Algae: Any of a large group of simple plants and plant-like organisms (like seaweed) that usually grow in water and produce chlorophyll like plants, but do not produce seeds.
Fungus: Member of the kingdom of living things (as mushrooms, molds, and rusts) that have no chlorophyll and must live in or on plants, animals, or decaying material.
Definitions From: Merriam-Webster Dictionary.