Desmarestia ligulata


One gloomy foggy April day in Still Water Cove, Monterey, CA a desmarestia ligulata was found in the drift on the beach.


I am in the class ‘Marine botany’ in Moss Landing Marine Labs, and this day we had our last field trip. This species of brown seaweed is commonly called flattened acid leaf because it contains sulfuric acid and its pH is between 0.8 and 1.8 . This range of pH is as low as human gastric juices, and it is so low that when urchins eat this seaweed, their teeth dissolve.

One of the mysteries of the universe is therefore; why do the urchins eat this seaweed, when their teeth dissolve? I do not think there is any scientific answers to this question yet, so I chose to believe it might be because it is so beautiful looking.


I think it looks very much like a frond that can be found in the forest, but the species is commonly found in low intertidal and subtidal regions from Alaska to Mexico and it can exceed 1 m (3 ft) in length. This species is an annual, and it is monoecious, which means that the female and the male structures are in the same individual. I took a picture of its hairs with the foldscope, and it shows the cells and growth quite clearly. This plant possesses apical growth, which is the same as can be seen in pinetrees. The growth is promoted by the apical meristem region of the thalli (plant).


The species has a low light threshold, which means that when light abundance decreases in the ocean, this plant often pops up. Light abundance can decrease as a consequence of excess nutrients in coastal environments – and therefore this seaweed is often a indicator of disturbance.

Therese Meyer

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