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Title: Postelsia  
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Subject: Peer review/Postelsia/archive1, Laminariaceae, Peer review/March 2007, Monotypic brown algae genera, Laminariales genera
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Sea palm
Postelsia palmaeformis growing in its native habitat at low tide
Scientific classification
Kingdom: Chromalveolata
Phylum: Heterokontophyta
Class: Phaeophyceae
Order: Laminariales
Family: Laminariaceae
Genus: Postelsia
Species: P. palmaeformis
Binomial name
Postelsia palmaeformis
Ruprecht 1852

Postelsia, also known as the sea palm (not to be confused with the southern sea palm) or palm seaweed, is a genus of kelp and classified within brown algae. There is only one species, Postelsia palmaeformis, found along the western coast of North America, on rocky shores with constant waves. It is one of the few algae that can survive and remain erect out of the water; in fact it spends most of its life cycle exposed to the air. It is an annual, and edible, though harvesting of the alga is discouraged.


  • History 1
  • Fossil record 2
  • Morphology 3
  • Life cycle and growth 4
  • Habitat 5
  • Epiphytes 6
  • Edibility 7
  • See also 8
  • References 9


One of Ruprecht's original drawings.

The sea palm was known by the natives of California by the name of Kakgunu-chale before any Europeans entered the region. Postelsia was first scientifically described by Franz Josef Ruprecht (1814–1870) in 1852 from a specimen found near Bodega Bay in California. Ruprecht, an Austro-Hungarian who became curator of botany at the Academy of Sciences in St. Petersburg in 1839, studied seaweed specimens collected by botanist Ilya Vosnesensky, and published a paper describing one seagrass and five seaweeds, one of which was Postelsia.[1] The sea palm has been used by several textbooks, such as the Campbell - Reece Biology textbook, as an example of multicellular protists, as well as an example of the class Phaeophyceae.

The binomial name of the sea palm, Postelsia palmaeformis, represents two things. The generic name honors Alexander Philipov Postels, an Estonian-born geologist and artist who worked with Ruprecht, while the specific name describes the alga's similarity in appearance to true palms.[1]

Fossil record

One of the more interesting puzzles in ichnotaxonomy, pertains to fossils from Monte Bolca a lagerstätte near Verona, which were originally named Zoophycos caput-medusae, and previously thought to be trace fossils, but were found to be plants instead and given the name Algarum by French zoologist Henri Milne-Edwards in 1866.[2] The type specimen collected by Italian paleobotanist Abramo Bartolommeo Massalongo before 1855 is at the Natural History Museum of Verona and was preserved in a lithographic limestone upper and lower slab.[2]

When Italian botanist Achille Forti (28 November 1878 Verona -11 February 1937 Verona) worked on the specimens in 1926, they were reinterpreted as close relatives of Postelsia, now known to be a brown algae, which had lived in the coastal waters of the Eocene sea.[2] Forti renamed the species Postelsia caput-medusae putting it in the genus Postelsia, which now has only one species, Postelsia palmaeformis.[2] The appearance of the plant fossil is a holdfast on the bottom, with a stem-like stipe between there and the fronds which are about 5 centimetres (2.0 in) to 10 centimetres (3.9 in).[2] In life, the fronds would have hung vertically when the tide is in but flop over the stipe when exposed by low tide.[2]

Curiously, other specimens from this deposit collected and described by Massalongo in 1855 were actually trace fossils, only this one specimen was Postelsia.[2]


Postelsia has two distinct sporangia held within these grooves. The gametophyte stage is microscopic, consisting of only a few cells. The gametophytes produce sperm and eggs to create new sporophytes.

Like all phaeophytes, sea palms use the pigments chlorophyll a, chlorophyll c, fucoxanthin, and carotenes in photosynthesis. Their cell walls are composed of alginate. They use laminarin and mannitol for storage.[5]

Life cycle and growth

Like most brown algae, Postelsia goes through alternation of generations, and is an annual species. The diploid sporophyte produces, through meiosis, haploid spores, which drip down through the grooves in the blades onto the substrate, which may be mussels, barnacles, or bare rock. These spores develop, through mitosis, into small, multicellular haploid gametophytes, male and female. The male and female gametphytes create sperm and eggs, respectively. The sperm of the male reaches the female egg and fertilizes, resulting in a diploid zygote, which develops into a new sporophyte.[5]

Postelsia are green in color as juveniles, and change to a golden brown as they age, reaching a height of 50 to 75 centimeters.[4]

As a Postelsia alga grows, it's stipe thickens in the same manner as a tree's trunk. The cells beneath the epidermis, called the meristoderm, divide rapidly to form rings of growth, again, like a tree. However, the greater flexibility of Postelsia's stipe over that of a woody tree makes for some distinct differences. Postelsia must be thicker than a tree of equal height in order to support itself. However, the stipe is very much more suited to the coastal habitat, as it allows the seaweed to bend with the constant wave action. Such an environment would cause the inflexible, woody tree to break.[6]

The blades of the new sporophyte grow from one or two initial blades by splitting. A tear forms in the middle of the blade at its base, which then continues along the entire length of the blade until it is split in two.[5]


Sea palms are found on the rocky shores of western California mussel.[7] Recent studies have shown that Postelsia grows in greater numbers when such competition exists - a control group with no competition produced fewer offspring than an experimental group with mussels; from this it is thought that the mussels provide protection for the developing gametophytes.[8] Alternatively, it is thought that the mussels may prevent the growth of competing algae such as Corallina or Halosaccion, allowing Postelsia to grow freely after wave action removes the mussels.[9]

The California mussel (Mytilus californianus), Postelsia's chief animal competitor.
When Postelsia release their barnacles, and rip them from the rocks when the waves come, gripping them with holdfasts of incredible strength.[5]


Two other, smaller brown algae, of the family Ectocarpaceae, Ectocarpus commensalis and Pylaiella gardneri, as well as the two red algae Microcladia borealis and Porphyra gardneri, are epiphytic on Postelsia. Pylaiella gardneri is an obligate epiphyte to Postelsia. As with all epiphytes, these algae are not harmful to Postelsia, and merely use the larger alga as a substrate to grow upon.[3]


Postelsia palmaeformis at low tide at California tide pools

The blades, and less often, the stipes,[10] of Postelsia are sometimes used in certain dishes, usually in California. In fact, it is considered to be very tasty by the Chinese community of San Francisco.[10] However, because Postelsia is a protected species, this is discouraged, as clipping the blades too low, below the meristem, prevents reproduction. Postelsia can regenerate blades cut above the meristem, but removing the blades can limit a sporophyte's ability to produce spores and contribute to subsequent populations. Postelsia has also been in danger of overharvesting at some points. It is illegal to harvest Postelsia in British Columbia, Washington and Oregon. Postelsia is a partially protected species in California.[5] In California, recreational harvesting is illegal, but commercial harvesting of the sea palm is legal. Between 2000 and 2001, it is estimated that between 2 and 3 tons of Postelsia were harvested in California. The blades are eaten raw or are dried, and dried blades sell for up to US$45 per pound. Commercial harvesters of Postelsia must purchase a US$100 license, pay a royalty to the State of California (US$24 per wet ton of algae harvested), and submit a monthly harvest log.[7][11]

An experiment done to try to prove or disprove the claims of Postelsia harvesters that their gathering methods are sustainable yielded results stating that recovery from collection depended greatly on the season of collection.[12]

See also


  1. ^ a b Silva, Paul C. Dickey, Kathleen. Miller, Kathy Ann. "Special Issue: Seaweeds." Fremontia - A Journal of the California Native Plant Society, Jan 2004. Vol. 32, No. 1. The California Native Plant Society. 28 Feb 2007.
  2. ^ a b c d e f g William Miller, III (13 October 2011). Trace Fossils: Concepts, Problems, Prospects. Elsevier. pp. 224–226.  
  3. ^ a b DeCew's Guide to the Seaweeds of British Columbia, Washington, Oregon, and Northern California, Center for Phycological Documentation, University Herbarium, University of California, Berkeley, 2002. 13 July 2007
  4. ^ a b Rupr."Postelsia palmaeformis", Multi-Agency Rocky Intertidal Network (MARINe). 2004. 16 July 2007
  5. ^ a b c d e Oehm, Sarah, "The Brown Alga, Sea Palm Postelsia.", Monterey Bay Aquarium Research Institute. 1999. Monterey Bay Aquarium Research Institute, retrieved 6 February 2013.
  6. ^ Ennos, A. Ronald, Elizabeth Sheffield "Plant Life". Blackwell Science Ltd. 2000. 13 July 2007.
  7. ^ a b Miller, Kathy Ann, revised by John O’Brien, 3. SEA PALM, Annual Status of the Fisheries Report, California Fish and Wildlife Department, 2002 revised, retrieved 6 February 2013.
  8. ^ Blanchette, Carol Anne, Postelsia palmaeformisSeasonal patterns of disturbance influence recruitment of the sea palm, , Department of Zoology, Oregon State University, 1995, retrieved 6 February 2013.
  9. ^ Paine, R.T., Postelsia palmaeformisHabitat Suitability and Local Population Persistence of the Sea Palm , Ecology, Vol. 69, No. 6. 1998. 6 February 2013.
  10. ^ a b Sea Food Foraging Recipes., Adventure Sports Unlimited, 2001, retrieved 6 February 2013
  11. ^ Miller, Kathy Ann, "Sea Palm." Annual Status of the Fisheries Report 2001, California Department of Fish and Wildlife, retrieved 6 February 2013.
  12. ^ Thompson, Sarah Ann, Karina J. Nielsen, Carol A. Blanchette, Brennan Brockbank, Heather R. Knoll. Postelsia palmaeformisEffects of commercial collection on growth and reproductive output of , Sonoma State University, University of California, Santa Barbara, 13 July 2007
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