Laminaria has a life history with a heteromorphic alternation of generation. The diploid thallus (top) forms unilocular sporangia in regions called sori on the blades. They are called unilocular meiosporangia (or unilocular zoosporangia). The zoospores produce haploid filamentous male or female gametophytes (center) that form gametangia of two types: the smaller male gametangia produce small biflagellate cells that function as sperm, and the female gametangia release large, nonmotile cells that function as eggs. The zygote germinates and forms the typical sporophyte kelp.

from: http://biodidac.bio.uottawa.ca/Thumbnails/showimage.cfm?File_name=PHAE002B&File_type=GIF