Phycoerythrin is a red pigment found in certain algae, particularly in red algae and some cyanobacteria. It is a type of phycobiliprotein that plays a crucial role in photosynthesis by capturing light energy and transferring it to chlorophyll for energy conversion. Phycoerythrin is often used as a fluorescent marker in various biochemical assays and research applications due to its bright fluorescence and stability.