Lichens as living partnerships
The lichen-forming fungus builds most of the thallus, retains water and minerals, and houses a photobiont that fixes carbon; cyanobacterial partners may also fix nitrogen. Other fungi and bacteria can be regular associates. Together they form structures and tolerances not obvious from either main partner alone.
Scope: A worldwide introduction to lichenized fungi and their photosynthetic partners. It begins with the classic fungus-plus-alga-or-cyanobacterium model, then includes associated yeasts and bacteria without implying that every detected microbe is an obligatory partner. Lichens are not plants, mosses, or a single taxonomic lineage. · Last updated
The classic partnership builds a new body
Fungal hyphae organize a crustose, leafy, or branching thallus around photosynthetic cells. A cortex can moderate light and water loss, while the photobiont contributes carbohydrates produced by photosynthesis. Lichen form is not just a fungus with algae stuck to its surface: development and physiology change in association, producing an integrated structure that neither main partner displays in the same way alone. [1][3]
Two partners are the beginning, not always the whole
Green algae are the most common principal photobionts, while cyanobacteria serve that role in a smaller fraction and can occur alongside green algae. Sequencing and microscopy also reveal bacteria, yeasts, and other fungi within thalli. Some are persistent and functional; others may be transient. Calling lichens multipartite ecosystems captures complexity but should not make every detected organism an equally necessary symbiont. [2][4]
Water controls when lichens are active
Lichens lack roots and protective water regulation like vascular plants. They absorb water and dissolved substances across the thallus, become metabolically active when hydrated, and tolerate drying by suspending much activity. This poikilohydric strategy helps many occupy exposed rock, bark, soil, and polar or desert surfaces, but species differ greatly in light, moisture, substrate, and pollution tolerance. [1][3]
Reproduction may separate or carry partners
Fungal fruiting bodies release spores containing only the fungal partner, which must encounter a compatible photobiont to rebuild a lichen. Vegetative fragments, soredia, and isidia can disperse fungal and photosynthetic cells together. The visible lichen is named taxonomically for its fungus, yet identification and ecology depend on the composite thallus. Moss growing among lichen remains a separate plant, even when their textures intermingle. [3][4]
Related guides
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Where this guide comes from
Source-checked editorial guide. Last updated . This guide teaches identification and field skills; it is not a substitute for expert verification when it matters.
- U.S. Geological Survey — Lichens in biological soil crusts ↗
- The New phytologist — How to build a lichen: from metabolite release to symbiotic interplay ↗
- Proceedings (Baylor University. Medical Center) — Evolving together: the biology of symbiosis, part 1 ↗
- Frontiers in microbiology — The Lichens' Microbiota, Still a Mystery? ↗
