algae common on temperate glaciers and perennial snow; its red color sometimes prompts people to call it watermelon snow.

The red algae (Rhodophyta, , from Greek: (rhodon) = rose + (phyton) = plant, thus red plant) are a large group of mostly multicellular, marine algae, including many notable seaweeds. Most of the coralline algae, which secrete calcium carbonate and play a major role in building coral reefs, belong here. Red algae such as dulse and nori are a traditional part of European and Asian cuisine and are used to make other products like agar, carrageenans and other food additives.