Rhodophyceans

Rhodophyceans, commonly known as red algae, are a large division of eukaryotic algae. They are predominantly multicellular, although some species are unicellular or colonial. A defining characteristic of rhodophyceans is the presence of phycoerythrins, pigments that give them their characteristic red or purplish hues, although some species can appear green, brown, or even black due to variations in pigment composition and accessory pigments. These pigments are crucial for photosynthesis, enabling them to absorb light wavelengths that penetrate deeper into water.

Rhodophyceans are found in a wide range of aquatic environments, from shallow coastal waters to the deep sea, and are also present in freshwater habitats. They are particularly abundant in marine ecosystems, where they play vital ecological roles, such as providing habitat, contributing to reef formation (coralline algae), and serving as a food source for many organisms. Their life cycles are often complex, involving alternation of generations. Economically, some rhodophyceans are harvested for food, such as nori, and for their carrageenan and agar, which are used as gelling agents in various industries.