Hildenbrandia rubra (Sommerfelt) Meneghini
Description: Rose-red or brownish-red crusts, 0.2-0.5 mm thick, of indefinite extent, closely adherent to substrate, without rhizoids; without surface markings.
Habitat: On rocks and stones at all tidal levels, often in splash zone in caves, and subtidal, widely distributed, extemely abundant, particularly in upper shore where it appears to be very tolerant to extremes of temperature, light and salinity.
Similar species: Difficult to distinguish from the closely-related Hildenbrandia prototypus Nardo (not included here), with which it frequently occurs.
Key characteristics: Thin, extensive crust with irregular outlines; only red crust that grows on rock in the upper half of the shore.