Print related Information Sheets — Algae Lichens and Mosses

Algae, lichens, and mosses can all form green or gray growth on outdoor surfaces, but they are biologically different. Identifying the group explains how it obtains resources, reproduces, and responds to moisture. This is a combined introductory comparison.

Three familiar appearances represent different systems

Feature	Algae	Lichens	Mosses
Biological identity	Several evolutionary lineages, mostly photosynthetic; not one natural taxonomic group.	A fungus-centered association with photosynthetic partners and other microorganisms.	Small nonvascular land plants in the bryophyte assemblage.
Main carbon source	Photosynthesis in most familiar forms; exceptions exist.	Photosynthetic partner supplies fixed carbon.	Photosynthesis by the moss plant.
Typical body	Single cells, colonies, filaments, or large multicellular thalli.	A thallus with crust-like, leaf-like, or shrubby form.	Leafy shoots or mats anchored by rhizoids.
Reproduction	Varies widely; cell division, spores, and sexual cycles.	Fungal spores or dispersal units carrying partners together.	Spores plus fragmentation or other vegetative propagules.
Water relationship	Many are aquatic; terrestrial films also occur.	Many tolerate drying and reactivate when wet.	Surface water is important; sperm usually need a water film.

Algae are a functional label with many branches

Green algae, red algae, and brown algae are not all equally closely related. Cyanobacteria, often called blue-green algae, are bacteria rather than eukaryotic algae. An algal bloom’s color does not identify its species or establish whether toxins are present.

Aquatic algae support food webs and cycle nutrients. Excess nutrients and favorable physical conditions can produce excessive growth. Treat a suspicious water bloom as an identification and water-quality problem, not as ordinary moss.

A lichen is more than a plant on bark

The fungal partner builds much of the structure and obtains carbohydrates from algae or cyanobacteria. Lichens absorb water and substances across their surfaces. Their sensitivity to environmental conditions makes some species useful indicators, but one lichen on a tree cannot diagnose local air quality.

Lichens on bark usually use the tree as a surface rather than feeding on its living tissue. Scraping them off can injure bark without improving the tree’s health. Investigate canopy condition and site stress separately.

Mosses are plants with a distinct life cycle

A moss has no true roots, flowers, or seeds. Rhizoids anchor it. The green leafy generation produces gametes; a dependent sporophyte forms a capsule that releases spores. Mosses include species of wet habitats, exposed rock, soil, bark, and seasonally dry settings.

Moss in a lawn often reflects shade, moisture, compaction, or weak grass growth; it does not prove acidic soil. Correct the site conditions if grass is the goal, or consider whether a moss-covered surface is suitable for that place.

Observe before removing

Photograph the growth closely and in its setting. Note substrate, wetness, sun exposure, texture, and whether it has leafy shoots, a crust, or filaments. A hand lens helps. Do not collect from protected sites or apply a pesticide solely because a harmless surface growth looks unfamiliar.