Type Locality: “in Confervis maris occidentalis” (Linnaeus, 1755)
Ochrophyta: Phaeophyceae: Ectocarpales: Chordariaceae: Leathesia marina
Leathesia difformis has a distinct appearance compared to most brown algae, and is quickly identifiable by its unique sac-like appearance. Typically referred to as the “Sea Cauliflower”, the yellowish skin, hollow body, and amorphous outward protrusion from its point of contact (seen in Figure 1) with its substrate sets it apart from most species found in the intertidal area (e.g. the specimen seen here and Figure two).
Leathesia marina is a species that is commonly found located along landmasses in the Atlantic and Pacific oceans. It has been found and noted most commonly along the coasts of Ireland and Spain. The species is annual, meaning it has a year-long life cycle that typically feature growth stages in the spring and/or summer, and typically resides on rocks or other algae in the high to low intertidal zones (areas exposed by the changes in tide), though it is somewhat rare in the higher part of the intertidal zone. It has also been documented several times in the area around San Juan since 1904, starting on the Island in July 1904, and continuing with findings at Turn Rock in 1916, Brown Island in 1921, Vancouver Island in 1939, Dallas Beach in 1961, Eagle Cove in 2013, and others.
The specimens prepared for this page have been pressed, dried, and preserved in the herbarium (repository for plant specimens) located in Friday Harbor Laboratories. The alternate IDs entered in PHYKOS are JLS 154 and JLS 161.
The members of Leathesia marina have been noted to maintain a yellowish-brown thallus of up to 10-12 cm in diameter, with mature specimens noted to maintain a somewhat spherical appearance with a hollow center. The thallus of the species contains 7-10 plurilocular sporangia, each of which has been measured to be around 30-45 µm long and 4-6 µm wide (Smith, 1944 & Albott and Hollenberg, 1976). The texture of the thallus is typically quite slippery, and is easily broken when bent, as opposed to many other members of the Phaeophycaeae.
Species of the Leathesia genus undergo a two-phase heteromorphic life cycle that involves the alternation of generations between two separate multicellular life stages. The two stages are called the sporophyte and gametophyte generations. During the sporophyte generation (the morphology of which can be observed here), multicellular haploid spores are produced via meiosis, which is how the alga spreads to different areas where it can maintain itself (Graham et al, 2009). After the spores have found a place to grow, they grow via mitosis into a multicellular haploid gametophyte generation, which is the form in which the species is typically seen in its habitat. At maturity in the gametophyte generation, the gametophytes will produce flagellate gametes that will mate to produce a diploid zygote, which will grow via mitosis into another sporophyte, starting the cycle anew(Graham et al, 2009).
Abbott, Isabella A. and Hollenberg, George J. 1976. Marine Algae of California. Stanford University Press, Stanford, California.
Graham, Linda E. and James M. and Wilcox, Lee W. 2009. Algae: Second Edition. Pearson Benjamin Cummings, San Francisco.
Smith, Gilbert M. 1944. Marine Algae. Stanford University Press, Stanford.
Molecular data: http://www.ncbi.nlm.nih.gov/nuccore/?term=Leathesia
John Luke Schaefer is an undergraduate at the University of Washington.