P O S T E L S I A
Postelsia's larger characteristic sporophyte stage has been shown to grow anywhere from 50 - 75 cm in height. (For a cartoon depiction of the microscopic gametophyte stage, check out Postelsia's life history!)
A hollow tube of parenchymatous tissue, the stipe appears to contain no conducting elements (no nutrient transport between holdfast and baldes occurs along its length). The primary function of the stipe is then as a support for the alga. Balanced between strength and flexibility, the stipe is extremely extensible, allowing the alga to both remain erect during low tide and withstand large wave forces without being snapped in two. As a wave crashes over the alga, the stipe bends over much like a blade of grass would in the wind, only to return to its characteristic stature once the wave has passed. It would seem that the need for such balance would be directly involved in size limitations of this alga.
Like the stipe, Postelsia's holdfast (comprised of haptera) exhibits great strength. Large and strong, it affords the palm an extremely strong connection to the substratum in order to maintain position in its harsh environment. Bare rock appears to be the best substratum for the holdfast, which has been described by some as almost burrowing into the rock to create its strong attachment.
The blades of the sea palm are grooved and often rough at the edges, having been frequently beaten by waves pounding through Postelsia's habitat. I observed development/division of the blades to be similar to what one might have seen in Macrocystis, the giant kelp. New branches are formed at the base, and their corresponding blades will divide and split down the length of the exisiting blade.
Blades are also the site of spore production and may therefore be referred to as sporophylls. Sporangia are located in the canyons of the grooves, down which spores then drip to the substratum once released. After spore release, the blade will erode. Experiments have shown that blades will regenerate if cut not too late in their lifecycle; new blades will also hold the capacity to produce spores.
sporangia in grooves of blades
copyright 1999 sarah oehm
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