Monterey Bay Aquarium Research Institute
Marine Botany

Enteromorpha: now Ulva

See Eur. J. Phycol. (August 2003) 38: 277-294. Linnaeus was right all along: Ulva and Enteromorpha are not distinct species.

When Enteromorpha first begins growing, it forms a single row of cells, this structure is monosiphonous. Soon after the monosiphonous filament is formed, longitudinal division of cells creates a two layered filament. Eventually, after more cell division the two cell layers separate to form a tube, forming the adult morphology.

The thallus of Enteromorpha is tubular with the wall of the tube a single cell layer thick. The thallus can be branched or unbranched, and there is a wide variety of forms within the genus. Enteromorpha is attached to the substrate by a disc-like holdfast. The holdfast is formed by the basal cell dividing into three or four holdfast cells which elongate and undergo further division.

The cells in Enteromorpha can vary in size and shape from species to species, and sometimes they will form regular linear series in a frond, while other times there is an irregular arrangement of the cells. Each cell contains a single chloroplast, varying in size depending on the size of the cell.

There is a variety of differences in the morphology of Enteromorpha, some of which are illustrated in the following photographs:

A single thallus of Enteromorpha. Note how the tube becomes more compressed at the top of the frond. To see a larger image, click on the image or click here.

Three separate thalli, all of these are of the species E. intestinalis. To see a larger image, click the image, or click here.

Another example of the spiral shape of the thallus in some species.

Enteromorpha growing on a rock in the intertidal zone in Stillwater Cove, at Pebble Beach, CA

More Enteromorpha, also in Stillwater Cove at Pebble Beach, CA.

A view of partially submerged Enteromorpha in Stillwater Cove at Pebble Beach, CA. This is some of the same Enteromorpha that was used to take pictures in the lab and under the microscope.

A different species of Enteromorpha, this picture was taken by Judith Connor at Elkhorn Slough. This is most likely E. prolifera, which is widespread in Elkhorn Slough and other sheltered habitats.

More E. prolifera, this picture was also taken by Judith Connor at Elkhorn Slough. The white algae in this picture is also Enteromorpha, it is just drying out, and turning white as it does so.

Last updated: Jun. 16, 2009