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Desmarestia aculeata (Witch's hair)
Desmarestia viridis (Stringy acid kelp or green acid kelp)
Copyright © 2007 Jan Holmes
These brown seaweeds produce and store sulfuric acid. When plants are stressed they release acid breaking down their own tissues and the tissues of other seaweeds nearby. Seaweeds that look like patchy “camouflage material” may be the victims of stressed, acid leaking Desmarestia. Many species of seaweed in our area are edible (although some are more tasty than others) but Desmarestia is one seaweed to avoid.
These two species of brown seaweed grow in the low to upper subtidal area attached to rocks with a discoid holdfast. D. aculeata is wiry and dark brown whereas D. viridis (pictured above) is more hair or string-like and olive or brownish green. They are both profusely branched and both can reach lengths over 120 cm (4 feet) but here is an easy way to tell the two apart without the aid of a hand lens or microscope. If you examine the branching pattern of a few selected branches look to see if the side branching is opposite (two side branches form a “Y” coming out of the side of a main branch at the same horizontal level) or alternate (side branches stagger up the main branch). D. aculeata has alternate branching whereas D. viridis has opposite branching (see photographs).
This
page was created by Jan Holmes on 1/7/07.
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