Rockweed

This is a small tufted brown alga. The fronds are rarely more than 4 mm wide narrow and grow up to thirty centimetres long. They do not include airbladders as in some other species of Fucus. The fronds are fairly rigid and cartilaginous, partially flattened, and olive green to yellowish green in colour. The plant is branched and has a basal discoid holdfast. The midrib is conspicuous and near the holdfast the stalk is narrowed because of the thickening of the midrib and the erosion of the margins. The apices of the frond are rounded and the swollen receptacles at the tips are yellowish and up to six centimetres long. Two sub-species have been recorded from Great Britain and Ireland: F. distichus ssp. anceps and F. distichus ssp. edentates, each with a distinctive form. The brown colour is due to the xanthophyll, fucoxanthin which masks the colour of the other pigments, beta-carotene, chlorophyll a and c and other xanthophylls. Fucus distichus has a high content of phlorotannins which may protect larger plants from grazing by periwinkles though young plants are susceptible.

In Great Britain, rockweed is found on northern coasts of Scotland and the north and west coasts of Ireland where it is found on rock faces and in rock pools in the upper littoral zone. It also occurs on the eastern coast of North America and on the west coast from Alaska to California.