Description: Thallus is a tuft of mostly unbranched, pigmented, uniseriate filaments growing on Fucus, up to 0.7 cm (0.28 in) tall. Large, elongate unilocular sporangia commonly occur on colorless branched basal filaments, but these can be seen only with a microscope. Habitat: This species can co-occur with Pylaiella littoralis, which is usually much longer and is always branched.