Ulvaria blyttii

Dark sea lettuce

Authority: (Areschoug) K.L.Vinogradova

A young thallus starts out as a sac and then splits into a blade expanding to least 30 cm (12 in) in diameter. The blade is a bright green, one cell layer thick (up to 72 μm), and almost opaque. When dried, the thallus can turn dark brown to almost black due to the presence of dopamine in cells.

Habitat

This species is found in the low intertidal and subtidal on protected and semi-protected coasts and is frequently found on pebble or cobble substrates.