Organisms that rely on light energy to fix carbon, and thus participate in primary production, are referred to as photoautotrophs.
Photoautotrophs exists across the tree of life. Many bacterial taxa are known to be photoautotrophic such as cyanobacteria and some Pseudomonadota (formerly proteobacteria). Eukaryotic organisms gained the ability to participate in photosynthesis through the development of plastids derived from endosymbiotic relationships. Archaeplastida, which includes red algae, green algae, and plants, have evolved chloroplasts originating from an ancient endosymbiotic relationship with an Alphaproteobacteria. The productivity of plants, while being photoautotrophs, is also dependent on factors such as salinity and abiotic stressors from the surrounding environment. The rest of the eukaryotic photoautotrophic organisms are within the SAR clade (Comprising Stramenopila, Alveolata, and Rhizaria). Organisms in the SAR clade that developed plastids did so through a secondary or a tertiary endosymbiotic relationships with green algae and/or red algae. The SAR clade includes many aquatic and marine primary producers such as Kelp, Diatoms, and Dinoflagellates.