Pacific rockweed
| Fucus distichus | |
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| Scientific classification | |
| (unranked): | SAR |
| Superphylum: | Heterokonta |
| Class: | Phaeophyceae |
| Order: | Fucales |
| Family: | Fucaceae |
| Genus: | Fucus |
| Species: | F. distichus |
| Binomial name | |
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Fucus distichus L. |
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| Synonyms | |
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Fucus distichus or rockweed is a species of brown alga in the family Fucaceae to be found in the intertidal zones of rocky seashores in the Northern Hemisphere, mostly in rock pools.
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.
This is a small tufted brown alga. The fronds are 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.
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.
Like other brown algae, there is an alternation of haploid and diploid generations. The haploid thalli form isogamous, anisogamous or oogamous gametes and the diploid thalli form zoospores by meiosis. Reproduction is seasonal, and receptacles start being formed in late autumn in response to short days. The gametes are of both sexes and when released, ova can survive and disperse for several days. It is thought that self-fertilisation often occurs in this species and once a zygote is formed it can only be dispersed over a limited distance. The plant dies back after reproducing and gets washed from its rock substrate by waves during the following winter.
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Wikipedia