Bladder on the Wrack, er... Rock - Fucus distichus

This Mystery Organism is Fucus distichus, the rockweed, or bladder wrack. Fucus is one of the most common genera of brown algae. Species of Fucus are found on seashores throughout the temperate northern hemisphere, where they commonly occupy areas of the middle to high intertidal zones.

The name ¥bladder wrack refers to the lobbed bladders found on many of the fronds. These serve as flotation for the fronds, but more importantly, they are are the regions of the organism where sexual reproduction takes place. The bladder itself is called a receptacle. Scattered over its surface are ¥conceptacles the dark spots seen in this back-lit photograph. Unlike many other algae, the dominant phase of rockweed is diploid, and the conceptacles represent sexual organs where meiosis produces gametes. In some species of Fucus, both eggs and sperm are produced in the same receptacle (the plant is thus bisexual) whereas in others, eggs and sperm are produced on separate plants.

For a program that outlines aspects of micro- and macro- algae, see our video, Branches on the Tree of Life: Algae. For a treatment of the evolution of eukaryotes that outlines new perspectives on the relation of the different algae groups see our program: The Domains of Life.