Desmarestia Morphology
Monterey Bay Aquarium Research Institute
Marine Botany


Morphology and Cellular Morphology

Index Taxonomy Life History Morphology Antarctica Acknowledgements

six seaweed pressings

Here are six photographs (click on the photos for a larger image) I took of seaweed pressings stored in the Gilbert M. Smith Herbarium at the Hopkins Marine Station. There are many pressings of Desmarestia species from Northern California in this herbarium. There are also a few specimens of Desmarestia from places such as La Jolla, California, Alaska, and even Woods Hole, Massachusetts. As shown above, there is substantial diversity of form in Desmarestia sporophytes. Gametophytes are microscopic (see Life History). These are the six species that occur in Northern California and Oregon. There is a seventh species not pictured above that has only been reported from Carmel, Monterey County called Desmarestia kurilensis which looks like D. viridis but its lower axis is cylindrical rather than flattened. There are over 40 species of Desmarestia that can be found all over the world and most of these are endemic to their location. If you want to be in the place that has the greatest diversity of Desmarestia, like I do, then you should go to Antarctica.
The photograph on the far right is Desmarestia ligulata of the variety ligulata and was collected by Freya Sommer at the end of February 2005 at the commercial wharf of Monterey and I made the pressing. Though you can't see it in the photo, there is a small snail and a hydroid that were living on the specimen that got pressed onto the sheet. Freya also saw some Desmarestia ligulata of the variety firma at this location. I went looking for Desmarestia at Breakwater Cove, Hopkins Beach, and the beach off of Coral street but the only time that I saw Desmarestia this winter was at Pebble Beach. I collected some of the Desmarestia ligulata I saw growing on a rock about 10 feet under water, but by the time I got it back to the lab about an hour later it was in bad shape. It had lost its dark olive brown color and was bright green and it was also falling apart. Many Desmarestia species have sulfuric acid in their cell vacuoles. If the alga is exposed to air, high temperature, or is physically damaged the sulfuric acid will destroy the algal tissues. Though the primary function of concentrating acid is unknown, work by Pelletreau and Muller-Parker shows that the sulfuric acid deters grazing of Desmarestia by sea urchins.

drawing of opposit branching and alternate branching

This drawing shows the two different forms of branching of the thallus of Desmarestia species (thallus is the term for a plant body that lacks differential tissue like roots and leaves). Branching of the thallus may either be opposite (shown on the left side of the drawing) as it is in Desmarestia ligulata var. ligulata, or branching may be alternating (shown on the right side of the drawing) as it is in Desmarestia latifrons. The construction of the thallus is pseudoparenchymatous, meaning the tissue is composed of branched filaments that resembles parenchyma – tissue formed by cell division in more than one plane.

What do we do when we find a specimen in the field? Section it! Go to Cellular Morphology to look under the microscope.

Index Taxonomy Life History Morphology Antarctica Acknowledgements

© 2005 Ashley Maloney

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