Trebouxia

Trebouxia is a genus of green algae in the class Trebouxiophyceae. It comprises numerous species that are among the most common photobionts (photosynthetic partners) in lichen symbioses, where a fungal partner, the mycobiont, provides structure and protection while Trebouxia furnishes carbohydrates through photosynthesis. In lichens, Trebouxia cells live inside the fungal thallus and contribute to the photosynthetic metabolism of the composite organism.

Morphology and ecology of Trebouxia taxa vary, but most are unicellular or form small colonies. They are typically green due to chlorophyll a and b and accessory pigments. Trebouxia species can occur as free-living algae in soil, on rocks, or in freshwater habitats, and they readily transition into a photobiont role when associated with a compatible fungal partner. Desiccation tolerance and rapid reactivation of photosynthesis are characteristic features that support their role in fluctuating environments where lichens are common.

Taxonomic diversity within Trebouxia is substantial, with multiple molecularly defined lineages. Trebouxia decolorans is a well-studied species frequently reported as a photobiont in a variety of lichen-forming fungi. Other lineages within the genus associate with different fungal partners, reflecting a range of host specificity in lichen symbioses.

Distribution is global, with Trebouxia photobionts found in temperate and tropical regions wherever lichens occur. Trebouxia has been central to research on lichen ecology and symbiotic specificity, contributing to understanding how photobiont identity influences lichen physiology, morphology, and resilience.