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PHYCOLOGICAL SOCIETY OF AMERICA

P O S T E L S I A

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Like most kelps, Postelsia exhibits a heteromorphic life history (alternating morphological stages) with a macroscopic sporophyte stage and a microscopic gametophyte stage. Postelsia is unusual in that it is an annual. Beginning in late spring/early summer, meiosis occurs in the sporangia, and haploid spores are released. These non-motile spores then drip down between groves in the blades, often landing fairly near the base of their "parent" sporophyte, resting on mussels, barnacles, other algae, or bare rock. Individual male and female haploid gametophytes develop from the spores soon after they settle. The microscopic filamentous gametophyte stage will survive through the remainder of the summer into winter/early spring, when mitosis will produce eggs in the oogonia and motile sperm in the antheridia and sexual reprosuction will occur. Sperm then find their way to the female gametophyte and fertilize the egg. The resulting diploid cell develops into the large characteristic sporophyte on the haploid female gametophyte. The sporophyte generally persists until winter, when increased wave force often rips the palm from its substratum.

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