I’ve talked about Flat or Spiral Wrack (Fucus spiralis Linnaeus) before but wasn’t able to show a good photograph of one of its defining features. Getting close-ups of details on the seashore is sometimes impossible – without lying full-length face-down in wet seaweed. So the last time I was on the beach I collected a few fronds of Flat Wrack, from the extensive beds of Fucoids that covered the flat rock platform on the eastern shore of Chapmans Pool, and took them home to get the photographs that I wanted in comfort.
The pictures above and below illustrate the way that the swollen granular reproductive bodies at the ends of the fronds in this species have a unique flat border – like a seam – around the edge. You can see this border both flat-on and edge-on in the photographs. In other characteristics Flat or Spiral Wrack could be mistaken for another species of Fucoid brown seaweed but it is the only one with this particular characteristic.
The rock platform on the eastern edge of Chapmans Pool in June was covered in an olive green carpet of short Fucoid seaweeds including, Toothed Wrack, Bladder Wrack, and Flat or Spiral Wrack.
You have to look closely to see that the seaweed bed is composed of all the different types of weed, growing together, and overlapping each other in a complex natural mosaic pattern.
In the picture below you can see the round pea-shaped air bladders that occur in Bladder Wrack. There are fronds like this on the left side of the picture. The golden yellow-green reproductive bodies on the forked tips of the Flat Wrack are quite distinct elsewhere in the photograph. Both seaweeds have a central midrib along the fronds.
Previously, Flat or Spiral Wrack was discussed in the earlier post Three brown seaweeds: Furbelows, Sea Belt & Spiral Wrack from Studland Bay in spring.
Revision of a post first published 5 June 2010
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