The red alga Bonnemaisonia hamifera has two very distinct life phases, which were once considered to be separate species. The sexually reproducing form, the gametophyte is more conspicuous, up to 200 mm tall, consisting of red, finely branched fronds, bearing conspicuous curved hooks. The asexually reproducing tetrasporangophyte grows as fine, irregularly branched filaments, 10-25 mm long. The tetrasporophyte was once known as Trailliella intricata, and occurs year-round, while the gametophyte only occurs in the warmer seasons. Bonnemaisonia hamifera is native to the Northwest Pacific, and was first recorded in England in 1893, and in North America in 1928. In the Atlantic it occurs from Newfoundland to Chesapeake Bay, and from Norway to Morocco. and throughout the Mediterranean and Black Seas. It is also established in the Azores, Argentina, and New Zealand. As a fast-growing epiphyte, which produces noxious antifeeding compounds, it has some impacts on seaweed communities, including effects on host plants and on grazing fauna.