Description: Thallus is a branched blade, reddish brown (almost black) to yellowish brown, tough, reaching 15 cm (6 in) tall; branching dichotomous to irregular. This perennial species arises from a Petrocelis-like base; female thalli have distinct bumps (papillae), like a rough washcloth. Habitat: One of our most common seaweeds, growing on rocks from the high to mid intertidal of semi-protected to semi-exposed habitats. Similar taxa: Mastocarpus spp., including unnamed low intertidal and tidepool species, and M. jardinii.