It is common to mistake the soft, green mats of moss for the colorful, crusty patches of lichen, as both often grow side-by-side on trees and rocks. Despite their visual similarity, the two organisms are fundamentally different life forms belonging to separate biological kingdoms. Moss is an independent, simple plant that photosynthesizes and grows alone. Lichen is a complex composite entity, a partnership resulting in a unique structure unlike either of its individual components.
Defining Moss
Moss is a non-vascular plant belonging to the division Bryophyta. It lacks the specialized tissues (xylem and phloem) that transport water and nutrients in larger plants. These tiny plants do not have true roots, stems, or leaves, but instead have simple, leaf-like structures and stem-like parts. Mosses anchor themselves to a substrate with thread-like structures called rhizoids, which function mainly for attachment rather than absorbing water and minerals.
The inability to efficiently transport water limits the moss’s size, forcing it to grow low to the ground in dense clumps or mats to conserve moisture. Moss absorbs water directly through its entire surface, much like a sponge, and relies on the surrounding environment for hydration. The green tissues are made of photosynthetic cells, allowing the moss to independently produce its own food using sunlight. Mosses represent the gametophyte generation, which is the dominant and longer-lived stage of the plant’s life cycle.
Defining Lichen
Lichen is a composite life form resulting from a symbiotic association between two or more partners. The bulk of the structure is formed by a fungus, known as the mycobiont. Within the protective layers of the fungus lives a photosynthetic partner, the photobiont, which is usually either a green alga or cyanobacterium.
The partnership is a highly organized structure where fungal filaments, called hyphae, create the body, or thallus, of the lichen. This fungal structure provides shelter, protection from the elements, and gathers moisture and minerals from the air and rain. The photobiont performs photosynthesis and produces carbohydrates, which it then shares with the fungus. This arrangement allows the lichen to colonize harsh, nutrient-poor environments where neither partner could survive independently. The unique physical form of the lichen—which can be crust-like (crustose), leaf-like (foliose), or shrubby (fruticose)—emerges only from this composite relationship.
Key Biological Differences
The fundamental difference between the two organisms lies in their classification and internal structure. Moss is classified in the Plant Kingdom as an independent, multicellular, non-vascular plant. Lichen, by contrast, is a composite entity where the dominant partner is a fungus, placing the organism in the Fungi Kingdom.
Their internal workings also contrast sharply. Moss is a single organism that obtains all resources independently through its own photosynthetic cells and surface absorption. Lichen is a functional miniature ecosystem, relying on a symbiotic sharing of resources where the fungus provides structure and protection, and the alga provides nutrition through transferred carbohydrates. This structural difference is visible under a microscope, revealing organized plant cells in moss, but layered fungal hyphae encasing scattered algal cells in lichen.