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Ascophyllum nodosum

"Knotted wrack"

The body of this brown alga is three-dimensional. Its color may be dark green, olive, or slightly yellow espically at the tips of the branches. The thallus has no midrib, but it does have a central axis with irregularly occuring side branches. The tips of the side branches will often be swollen (receptacles) and covered with small dots (conceptacles). You can determine the age of one of these organisms by counting the number of air vesicles along the main axis: one air vesicle per year.