Life History

Generally, the life cycles of brown algae are complicated to say the least.  This alga is no different in that it has heteromorphic life stages, one of which being the microscopic, filamentous gametophyte which has not been depicted visually in the literature.  The structure that is commonly observed in the field is the sporophyte thallus.  Immature thalli exhibit no dark bumps on the surface, but once they mature, the darker bumps that are produced are reproductive structures called sori.  These structures are approximately 1 mm in diameter and are produced fairly evenly over the entire structure of the plant.  Club-shaped sterile hairs composed of 6-14 cells called paraphyses, line the outside of each sorus.  Located in the interior of the sorus are unangia, unilocular reproductive structures that produce large numbers of zoospores via meiosis.  These motile spores can then disperse away from the parent plant to settle and grow on suitable substrate for the filamentous, microscopic gametophyte.  The gametophyte, once mature, bears plurangia, plurilocular reproductive structures that produces gametes via mitosis.  These gametes fuse together during fertilization to form the sporophyte once again. This life cycle is illustrated below. (Abbott, 1976)