Species description: Gametangial phase is bright to dark red and feathery with many branches, to 20 cms in length. It has a soft, delicate texture. Branches spirally in pairs of unequal length. Some branches form reflexed hooks by which it attaches itself to other algae. The tetrasporangial phase Trailliella is brownish-red, monosiphonous, irregularly branched with the appearance of a cotton wool-like tuft, and although only a few cms long is readily identified by the small colourless cell at the upper end, and set to the side, of each cell.

Habitat: Gametangial phase usually attached to other algae in the sublittoral or occasionally low littoral, in rockpools. Tetrasporangial phase usually epiphytic in lower littoral and sublittoral to 8 m.

Distribution: Widely recorded on all coasts around Northern Ireland. First reported on from south coast of Britain in 1893 and reported from: England, except on the east coast, Ireland, Scotland, Wales, Isle of Man and the Channel Islands. Europe: Mediterranean, Atlantic coasts of Spain and France, Netherlands (drift), Helgoland, Baltic Sea, Norway, the Faroes and Iceland. Atlantic coast of North America: Canada, Maine, New Hampshire, Massachusetts, Connecticut, Long Island and Virginia, Canary Islands, South Africa and Japan.

Similar Species: Could potentially be confused with Bonnemaisonia asparagoides but it does not have the reflexed hooks. The tetrasporangial phase could be very easily confused with the tetrasporangial phase of Asparagopsis armata and these require microscopic examination to distinguish between them.

Key Identification Features:

• Gametangial phase shows some branches forming reflexed hooks.
• Tetrasporangial phase shows colourless cells at the upper end of each cell.

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

iNaturalist: Bonnemaisonia hamifera at iNaturalist World Species Observations database.

WoRMS: Bonnemaisonia hamifera at World Register of Marine Species. Accepted name: Bonnemaisonia hamifera Hariot, 1891. AphiaID: 144442.

Classification: Biota; Plantae; Biliphyta; Rhodophyta; Eurhodophytina; Florideophyceae; Rhodymeniophycidae; Bonnemaisoniales; Bonnemaisoniaceae; Bonnemaisonia