FHL Marine Botany  ::::::::::::::::::::::::::::::   Taxonomy | Habitat | Morphology | Life History | Ecology | Biochemistry




Fig 5. Fucus distichus overlaying a dense mat of barnacles photographed during low tide at Cattle Point, Friday Harbor. Notice the prominent percurrent midrib, flattened thallus and swollen receptacles


Longitudinal cross section of F. distichus thallus showing the three distinct dermal layers. Rule 120 µm


Multiple medullary elements running parallel to the thallus; note the cup-like joints characteristic of the sieve elements. Rule 50 µm


Longitudinal cross section of F. distichus thallus showing medullary element with sieve plate. Rule 50 µm



General Morphology

F. distichus demonstrates dichotomous branching in one plane with a narrow stalk that terminates in a discoid or irregularly shaped holdfast (3).  The thallus is flattened with an evident percurrent midrib extending from the most distal portion down to the holdfast (2).  The flattened wings of the thallus often bear randomly scattered sterile conceptacles, while the most distal portion of the thallus is markedly swollen during fertility (3).  The swollen portion of the thallus or receptacle harbors the conceptacles, which are the small bumps covering the receptacle in figure 5. Swelling is a result of abundant mucilage production by the conceptacles (1). The conceptacles produce the reproductive female oogonia and male antheridia (3).








Dermal Tissue

The cellular organization of F. distichus is analogous to other algae in the order Fucales.  My longitudinal cross section displays three distinct dermal layers.  The outermost epidermis is tightly packed and green in color due to the chlorophyll in the endogenous chloroplasts.  The cortex is comprised of irregularly shaped packed cells with increased interstitial space.  The most internalized layer is the medulla, which exhibits a high volume of interstitial space and very loosely packed elongated cells (1). 








Sieve Elements

Fucus distichus is able to translocate organic material via a mechanism similar to that exhibited by the order Laminariales (1).  The medullary elements have terminal sieve plates, which form a continuous system of cytoplasm for the longitudinal and transverse translocation of organic matter (1).
























  1. Vijayaraghavan, M.R. et al.  Brown Algae: Structure, ultrastructure and reproduction.  APH Publishing Corp 1998.

  2. Lee, R.E.  Phycology: 2nd Edition.  Cambridge University Press 1980, 1989.

  3. Fritsch, F.E.  The Structure and Reproduction of the Algae.  Cambridge University Press 1959.