Picture of a M. pyrifera showing the typical growth

Macrocystis pyrifera is a perennial kelp and has an alternation of generations; one being hapliod (1n) and the other diploid (2n).  The reproductive sori are located closer to the holdfast of the kelp.  In the sporangium the sori occur and the zoospores are released to settle on the bottom and develop into gametophytes.  There are a “male” and a “female” which are called antheridia and oogonia.  The fertilization of the two would give a zygote, which will grow into a sporophyte.