Description: Thallus filamentous, ecorticate, erect and delicate. Attached by aprostrate axes and grows to 5 cms long with branches in opposite pairs, quite densely tufted. Gland cells abundant.

Habitat: Uncommon. Generally epiphytic from midl-littoral to 10 m depth.

Distribution: Recorded from sites scattered around the British Isles. Europe: Mediterranean, Black Sea, Netherlands and Sweden. Atlantic coast of North America: Canada, Maine, New Hampshire, Massachusetts, Rhode Island, Connecticut, New Jersey, Virginia and North Carolina. Further afield: Canary Islands and Morocco. Recently introduced to South Australia.

Similar Species: Antithanmion densum and Antithamnion villosum are similar having opposite branchlets.

Key Identification Features:

• Each pair of opposite branches are at right angles to the next pair. The gland cells on the final branchlets are abundant.

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

iNaturalist: Antithamnion cruciatum at iNaturalist World Species Observations database.

WoRMS: Antithamnion cruciatum at World Register of Marine Species. Accepted name: Antithamnion cruciatum (C.Agardh) Nägeli, 1847. AphiaID: 144509.

Classification: Biota; Plantae; Biliphyta; Rhodophyta; Eurhodophytina; Florideophyceae; Rhodymeniophycidae; Ceramiales; Ceramiaceae; Ceramioideae; Antithamnieae; Antithamnion