O S T E L S I A
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.
copyright 1999 sarah oehm
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