Lichens—these cold-hardy, slow-growing, yet long-lived organisms—are often confused by people with certain species of fungi or mosses. They are composed of fungal hyphae and cells of algae, mostly green algae. Admittedly, they also contain other organisms. Unlike plants, lichens have no roots, stems, branches, or leaves. No lichen has leaves, yet the body of a lichen is conventionally referred to as a thallus.