Lomentaria orcadensis (Harvey) F.S. Collins ex W.R. Taylor
Description: Compressed crimson frond, to 40 mm long (usually much smaller).
Frequently ovate, with flattened lateral branches distally, arising from creeping,
narrowly cylindrical stolons. Main fronds and branches with narrow bases
and blunt apices, hollow, with consticted nodes. Tetrasporgangia formed in sori. Male and cystocarpic plants not known in Britain and Ireland.
Habitat: On rock and Laminaria hyperborea holdfasts, silty lower intertidal pools and subtidal, on exposed shores. Widely distributed; probably frequent but often overlooked due to its small size.
Picturesop: Northern Ireland © Bernard Picton, Ulster Museum; bottom: Chimney Rocks, Penzance, Cornwall © David Fenwick.