Lichens are pioneer organisms that can colonize bare rock surfaces, often forming the first biological layer in an ecosystem and initiating soil formation. Mosses, particularly species of Sphagnum, can also grow on sterile substrates like rocks or sand, retaining moisture and contributing to substrate development. Ferns typically require more developed soil for their root systems, and mushrooms, being fungi, are saprophytic or parasitic and usually grow on decaying organic matter or soil, not directly on sterile surfaces without any preceding biological colonization.