Description: Thallus is a thin-walled, tan-colored sac that is flattened and tapers to a short stipe and inconspicuous disc-like (discoidal) holdfast. The thallus averages 15 cm (5.9 in) but has been observed in Alaska up to 50 cm (20 in) tall. Habitat: This annual occurs in spring, usually on mid to low intertidal cobble or pebble in areas that remain damp at low tide in protected habitats. This species is not epiphytic on other seaweeds. Similar taxa:  Colpomenia bullosa, Petalonia, Coilodesme sp.