German Alga of the Year 2026: Trebouxia – a hidden powerhouse in lichens and a specialist for extreme habitats

The Phycology Section of the German Botanical Society (DBG) has chosen the green alga Trebouxia as Alga of the Year 2026. This brings into focus a group of organisms that has played a central role in the colonization of Earth for millions of years—usually unnoticed, hidden within the diverse bodies of lichens. Trebouxia is the most common photobiont partner of lichen-forming fungi and thus a key driver of entire ecosystems. Dr. Patrick Jung, an algal and lichen researcher at the University of Applied Sciences Kaiserslautern, investigates how algae such as Trebouxia manage to grow in some of the most extreme locations on our planet and, in doing so, fulfill important functions for their environment and the emergence of ecosystems.

No lichens without algae

Lichens are survival specialists: they grow where many other life forms fail—on bare rock, in Arctic tundra, at high elevations, or in arid desert regions. The basis for this remarkable resilience is a symbiosis of fungi, a green alga or cyanobacterium, and additional microorganisms such as bacteria. While the fungal partner provides the protective framework of the lichen, an alga sits inside as the “green powerhouse” of the community. Trebouxia cells contain a chloroplast and perform photosynthesis. The sugars and other energy-rich compounds produced in this way serve as nutrients for all partners in the lichen association.

The unicellular genus Trebouxia is among the most common photobionts worldwide—that is, photosynthetically active partners of lichen-forming fungi. Without Trebouxia, many of the roughly 30,000 known lichen species would not exist. This great diversity is no coincidence: the alga is physiologically unusually flexible. It can survive long periods of drought, is surprisingly tolerant of intense UV radiation and temperature fluctuations, and can repeatedly adjust its activity to changing environmental conditions.

Trebouxia points to environmental pollution

From the outside, lichens often appear unremarkable, but inside Trebouxia is highly active. This invisible performance is more significant than one might initially assume—not only for the lichen itself, but also for us. The genus Trebouxia shows species-specific responses to heavy metals, allowing conclusions to be drawn about patterns of environmental contamination. In addition, its genetic variants are studied in order to detect climatic shifts. Above all, the alga plays an important role in measurements of air quality, because lichens are very sensitive to air pollutants such as nitrogen oxides, and many air-purity monitoring programs are based on the presence of certain lichen species with Trebouxia as their photobiont. By supplying these species with energy, the alga becomes a quiet partner in modern environmental surveillance.

Important pioneering work in extreme habitats

Trebouxia does not occur only under the protection of the lichen symbiosis. Even at extreme sites, free-living Trebouxia cells have been discovered—on rock surfaces, in the dust of fine biological soil crusts, or in ice-free polar microhabitats. The fact that a unicellular green alga can persist both in association with fungi and alone under the harshest conditions makes it an exciting model organism. Researchers have recently sequenced the genome of Trebouxia to better understand this. For questions in stress biology and symbiosis research, scientists are investigating how Trebouxia protects its photosynthetic apparatus when water is lacking or sunlight is particularly intense. Among other findings, they have identified a particularly strong enrichment of stress pigments from the xanthophyll cycle, robust repair processes of photosynthetic proteins, and unusual storage compounds such as sugar alcohols that are typical for many Trebouxia species and help them become active again even after prolonged desiccation.

The patron of this year’s alga, Patrick Jung, has been dedicated for years to the extremophilic properties of Trebouxia. His work shows how this alga enables the survival and occurrence of lichens in especially hostile regions and what contribution it makes there to carbon cycling. Lichens—and thus Trebouxia—play, for example, an important role in the formation of new soils. On bare rock they slowly release minerals needed for growth, and the first fine humus layers develop. In many regions of the world, Trebouxia is therefore indirectly involved in the formation of the soil that later provides plant roots with anchorage and nutrients. In polar regions, Trebouxia and its fungal partners can account for a substantial proportion of annual primary production—that is, the biomass that forms the foundation for further food chains. These insights cast the tiny alga, as a pioneer colonizer, in a new light: it operates where few organisms are active and thereby supports not only its symbiotic partners but also other organisms as a food resource.

An important model organism for science

Trebouxia also offers exciting research prospects for the future. Some of its protective mechanisms against radiation or desiccation could inspire biotechnological applications—for example, materials that must tolerate extreme conditions. In addition, the alga is increasingly used to explore how life might function on other planets or moons. Its ability to survive for many months in a dried-out state makes it a candidate for experiments on the long-term stability of photosynthetic cells beyond Earth.

By choosing Trebouxia as Alga of the Year 2026, the Phycology Section of the DBG highlights how significant microscopic organisms can be. Trebouxia shows that even cells invisible to the naked eye can drive fundamental processes on our planet—from photosynthesis and soil formation to the colonization of extreme habitats. The award honors an alga that is often overlooked, yet belongs worldwide to the unseen forces that shape landscapes and enable life in extraordinary regions.