Phylum Rhodophyta, Class Florideophyceae, Order Gigartinales, Family Phyllophoraceae
Tetrasporophyte life history phase of Mastocarpus papillatus is a crust 2-2.5 mm thick, dark black-red to olive brown. Formerly thought to be a separate species, Petrocelis.
Abundant; crusts cover large areas of rock surfaces in high and mid-intertidal zones around bases of erect algae; protected & exposed outer coast.
Geo Range: Alaska to Baja
Synonyms: Petrocelis franciscana
Similar species: other reds (e.g. Mastocarpus jardinii, Pikea) also have crustose phases in their life histories, making field identification to species level difficult.
Image: Corallina(pink erect coralline throughout); blades of Phyllospadix scouleri (surf grass, rt side)