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Postelsia palmaeformis - Sea palm

Geographic range:
Hope Island, British Columbia to San Luis Obispo County, California

Key features:
Brown, short, thick and round stipe (often to 30 cm tall) topped with dozens of blades that hang downwards, often to the rocky reef itself.

Similar species:

exposed rocky shore
Postelsia palmaeformis - Sea palm image


Primary common name:
Sea Palm
  ITIS code:
Synonymous name(s):
General grouping:
Brown seaweed/algae

Geographic Range
Range description:
Postelsia palmaeformis is found from Hope Island, British Columbia to San Luis Obispo County, California.
Northern latitude extent:
  Southern latitude extent:
East longitude extent:
  West longitude extent:

Intertidal Height
Lowest intertidal height:
0 meters OR -2 feet
  Highest intertidal height:
0 meters OR -1 feet
Intertidal height notes:
Postelsia palmaeformis is usually found in the low intertidal, but in some areas can exist into the mid intertidal.

Subtidal Depth Range
Minimum depth:
0 meters OR 0 feet
  Maximum depth:
0 meters OR 0 feet
Subtidal depth notes:
Not found subtidally.

exposed rocky shore
Habitat notes:
Postelsia palmaeformis is abundant in exposed rocky habitats from the mid to low intertidal. This kelp forms dense stands during the summer in areas that are pounded by surf. Postelsia palmaeformis can also grow in clumps in beds of the California mussel Mytilus californianus.

Relative abundance:
It can be locally abundant, but is relatively rare in central California.

Species Description
General description:
Postelsia palmaeformis is an annual kelp that resembles miniature palm trees. Palmaeformis literally means: having the shape of a palm tree. This brown algae will form dense stands during the summer in rocky habitats pounded by surf.
Distinctive features:
Postelsia palmaeformis has a small, stout, and densely branched holdfast that supports a hollow cylindrical stipe. The top of the stipe has numerous branches, each of which carries a single, narrow, dropping blade. A single individual can have up to one hundred blades or more, each up to 25 cm long. Additional blades can be produced through the splitting of pre-existing blades. These blades are covered with longitudinal grooves that contain sporangia.
Postelsia palmaeformis grows up to 60 cm tall.

Natural History
General natural history:
The tough and flexible stipe of Postelsia palmaeformis is extremely resistant to wave shock. Postelsia palmaeformis provides protection for other species enabling them to survive in an environment otherwise too rigorous on account of surf. Postelsia palmaeformis will often settle onto other algal and animals species, it is particularly abundant in patches within beds of Mytilus californianus. By settling onto and among other species, Postelsia palmaeformis increases the probability of both being ripped from the substratum and overgrowing and smothering other species. The end result is a clear substratum for the use of sporophytes of their own species.
Postelsia palmaeformis is considered a delicacy. The stipe and the blades can be pickled, steamed or eaten fresh. In California Postelsia palmaeformis is protected and unlicensed harvesting is prohibited due to its popularity as an edible.

Feeding behavior
Feeding behavior(s):
Feeding behavior notes:
April - May  
Spores of Postelsia palmaeformis develop in grooves on both sides of the blades in late spring. They are released during low tide, dripping down onto nearby rocks and adhering quickly. Therefore, most dispersal is limited to distances of 1 to 5 meters. Long-distance probably only occurs as a result of floating individuals that have been ripped off the substratum. Within a clump of Postelsia palmaeformis, the individuals are siblings.
Dayton, P. 1973. Dispersion, dispersal, and persistence of the annual intertidal alga, Postelsia palmaeformis Ruprecht. Ecology 54: 433-438.

Mondragon, J. 2003. Seaweeds of the Pacific Coast: common marine algae from Alaska to Baja California. Sea Challengers, Monterey, CA. 97 p.

O\'Clair, R.M. 2000. North Pacific Seaweeds. Plant Press, Auke Bay, Alaska. 162 p.

Ricketts, E. F., J. Calvin, and J.W. Hedgpeth. 1985. Between Pacific tides. Stanford University Press, Stanford, CA. 652 p.

Data supplied by SIMoN Sanctuary Integrated Monitoring Network
Anthopleura xanthogrammica - Giant green anemone

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