Aglaothamnion tenuissimum is a red seaweed growing in delicate, finely branched tufts, 30-80 cm tall. It often grows on seagrasses (Zostera spp. or other seaweeds. It is widely distributed in the North Atlantic In 1978, it was discovered in San Francisco Bay, where it is established. Populations in Brazil and Australia are considered cryptogenic.
Image Credit: Natural History Museum, London via the Creative Commons (CC BY 4.0) license