Description: Crustose, thin and firmly attached by the whole undersurface to rock. Very dark red. Surface smooth but with sunken conceptacles just visible with hand lens.

Habitat: Common. Epilithic from the upper littoral; into the sublittoral.

Distribution: Widespread in the British Isles. Europe: Mediterranean, Portugal, Atlantic coasts of Spain and France, Netherlands, Baltic Sea, Norway, Faroes, Spitzbergen and Iceland. Greenland. Atlantic coast of North America: Canada, Maine, New Hampshire, Massachusetts, Connecticut and Long Island, New Jersey, Delaware, Maryland and Virginia. Further afield: Jamaica and Canary Islands. Possibly world-wide.

Similar Species: Almost identical to Hildenbrandia crouaniorum and the freshwater species Hildenbrandia rivularis distinguished only by the manor of division of the tetraspores.

Key Identification Features:

• Very small conceptacles in thin crustose thallus.

Distribution Map from NBN: Hildenbrandia rubra at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Hildenbrandia rubra at iNaturalist World Species Observations database.

WoRMS: Hildenbrandia rubra at World Register of Marine Species. Accepted name: Hildenbrandia rubra (Sommerfelt) Meneghini, 1841. AphiaID: 145712.

Classification: Biota; Plantae; Biliphyta; Rhodophyta; Eurhodophytina; Florideophyceae; Hildenbrandiophycidae; Hildenbrandiales; Hildenbrandiaceae; Hildenbrandia