Postelsia
Encyclopedia
Postelsia, also known as the sea palm (not to be confused with the southern sea palm) or palm seaweed, is a genus of kelp
. There is only one species, Postelsia palmaeformis. It is 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. Postelsia is a partially protected species in California
.
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. The sea palm has been used by several textbooks, such as the Campbell - Reece Biology textbook, as an example of multicellular protist
s, 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.
- one for its diploid, monoicous
sporophyte
stage, which is the dominant portion of the life cycle, and one for its smaller, haploid, dioecious
gametophyte
stage. Like all seaweeds, the sporophyte stage of Postelsia consists of a thallus, which is made up of a stem-like stipe
topped with possibly over 100 leaf-like blade
s, and rests on a root-like holdfast
. The holdfast anchors the organism to the rocks it lives on. The sea palm has no vascular
system; the stipe is only for support of the organism and holds the fronds up over other organisms so they can receive more light. The stipe is merely a firm, hollow tube, able to withstand the open air of low tide conditions as well as the crashing waves of high tide. The blades are grooved, with the 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 pigment
s chlorophyll
a, chlorophyll c, fucoxanthin
, and carotene
s in photosynthesis
. Their cell wall
s are composed of alginate. They use laminarin
and mannitol
for storage.
, and is an annual species. The diploid sporophyte produces, through meiosis
, haploid spore
s, which drip down through the grooves in the blades onto the substrate, which may be mussel
s, barnacle
s, 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.
Postelsia are green in color as juveniles, and change to a golden brown as they age, reaching a height of 50 to 75 centimeters.
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 Postelsias 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.
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.
, from as far north as Vancouver Island
, to the southern central coast of California. They live in the middle to upper intertidal zones in very wavy areas. High wave action may increase nutrient availability and moves the blades of the thallus, allowing more sunlight to reach the organism so that it can photosynthesize. In addition, the constant wave action removes competitors, such as the mussel
species Mytilus californianus. 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. 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.
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When Postelsia release their spores, they tend to fall within a few meters of the parent sporophyte, for two reasons. The first is that though spores are flagellated and can swim, they are often released at low tide and are deposited directly to the substrate below. Secondly, Postelsia gametophytes need to be close to each other in order for fertilization to occur. As such, sea palms tend to live very close to each other in large aggregations. Some juvenile sporophytes will grow on competing organisms, like mussels or barnacle
s, and rip them from the rocks when the waves come, gripping them with holdfasts of incredible strength.
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.
The blades, and less often, the stipes, 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. 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. 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.
Though some Postelsia harvesters claim their methods of gathering are sustainable, there is no scientific evidence to support these claims. An experiment done to try to prove or disprove such sustainability yielded results stating that recovery from collection depended greatly on the season of collection.
Kelp
Kelps are large seaweeds belonging to the brown algae in the order Laminariales. There are about 30 different genera....
. There is only one species, Postelsia palmaeformis. It is found along the western coast of North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, on rocky shores with constant waves. It is one of the few algae
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
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. Postelsia is a partially protected species in California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
.
History
Franz Josef Ruprecht
Franz Josef Ruprecht was an Austrian-born physician and botanist active in Russia, where he was known as Frants Ivanovič Ruprekt . He grew up, studied, and graduated as Doctor of Medicine in 1836 in Prague...
(1814–1870) in 1852 from a specimen found near Bodega Bay
Bodega Bay
Bodega Bay is a shallow, rocky inlet of the Pacific Ocean on the coast of northern California in the United States. It is approximately across and is located approximately northwest of San Francisco and west of Santa Rosa...
in California. Ruprecht, an Austro-Hungarian who became curator of botany at the Academy of Sciences in St. Petersburg in 1839, studied seaweed
Seaweed
Seaweed is a loose, colloquial term encompassing macroscopic, multicellular, benthic marine algae. The term includes some members of the red, brown and green algae...
specimens collected by botanist Ilya Vosnesensky, and published a paper describing one seagrass
Seagrass
Seagrasses are flowering plants from one of four plant families , all in the order Alismatales , which grow in marine, fully saline environments.-Ecology:...
and five seaweeds, one of which was Postelsia. The sea palm has been used by several textbooks, such as the Campbell - Reece Biology textbook, as an example of multicellular protist
Protist
Protists are a diverse group of eukaryotic microorganisms. Historically, protists were treated as the kingdom Protista, which includes mostly unicellular organisms that do not fit into the other kingdoms, but this group is contested in modern taxonomy...
s, 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
Alexander Philipov Postels
Alexander Filipov Postels , was a Russian naturalist, mineralogist and artist.Postels studied at St.Petersburg University and in 1826 lectured there on inorganic chemistry....
, an Estonian-born geologist and artist who worked with Ruprecht, while the specific name describes the alga's similarity in appearance to true palms.
Morphology
Postelsia has two distinct morphologiesMorphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
- one for its diploid, monoicous
Monoicous
Monoicous is a botanical term used to describe plants which bear both sperm and eggs on the same gametophyte. Dioicous is the complementary term describing species in which gametophytes produce only sperm or eggs but never both. The terms are used largely but not exclusively in the context of...
sporophyte
Sporophyte
All land plants, and some algae, have life cycles in which a haploid gametophyte generation alternates with a diploid sporophyte, the generation of a plant or algae that has a double set of chromosomes. A multicellular sporophyte generation or phase is present in the life cycle of all land plants...
stage, which is the dominant portion of the life cycle, and one for its smaller, haploid, dioecious
Dioecious
Dioecy is the property of a group of biological organisms that have males and females, but not members that have organs of both sexes at the same time. I.e., those whose individual members can usually produce only one type of gamete; each individual organism is thus distinctly female or male...
gametophyte
Gametophyte
A gametophyte is the haploid, multicellular phase of plants and algae that undergo alternation of generations, with each of its cells containing only a single set of chromosomes....
stage. Like all seaweeds, the sporophyte stage of Postelsia consists of a thallus, which is made up of a stem-like stipe
Stipe (botany)
In botany, a stipe is a stalk that supports some other structure. The precise meaning is different depending on which taxonomic group is being described....
topped with possibly over 100 leaf-like blade
Blade
A blade is that portion of a tool, weapon, or machine with a cutting edge and/or a pointed tip that is designed to cut and/or puncture, stab, slash, chop, slice, thrust, or scrape animate or inanimate surfaces or materials...
s, and rests on a root-like holdfast
Holdfast
A holdfast is a root-like structure that anchors aquatic sessile organisms, such as seaweed, other sessile algae, stalked crinoids, benthic cnidarians, and sponges, to the substrate. ...
. The holdfast anchors the organism to the rocks it lives on. The sea palm has no vascular
Vascular tissue
Vascular tissue is a complex conducting tissue, formed of more than one cell type, found in vascular plants. The primary components of vascular tissue are the xylem and phloem. These two tissues transport fluid and nutrients internally. There are also two meristems associated with vascular tissue:...
system; the stipe is only for support of the organism and holds the fronds up over other organisms so they can receive more light. The stipe is merely a firm, hollow tube, able to withstand the open air of low tide conditions as well as the crashing waves of high tide. The blades are grooved, with the sporangia
Sporangium
A sporangium is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. All plants, fungi, and many other lineages form sporangia at some point in their life cycle...
held within these grooves. The gametophyte stage is microscopic, consisting of only a few cells. The gametophytes produce sperm
Sperm
The term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...
and eggs
Ovum
An ovum is a haploid female reproductive cell or gamete. Both animals and embryophytes have ova. The term ovule is used for the young ovum of an animal, as well as the plant structure that carries the female gametophyte and egg cell and develops into a seed after fertilization...
to create new sporophytes.
Like all phaeophytes, sea palms use the pigment
Pigment
A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...
s chlorophyll
Chlorophyll
Chlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...
a, chlorophyll c, fucoxanthin
Fucoxanthin
Fucoxanthin is a xanthophyll, with formula C42H58O6. It is found as an accessory pigment in the chloroplasts of brown algae and most other heterokonts, giving them a brown or olive-green color...
, and carotene
Carotene
The term carotene is used for several related unsaturated hydrocarbon substances having the formula C40Hx, which are synthesized by plants but cannot be made by animals. Carotene is an orange photosynthetic pigment important for photosynthesis. Carotenes are all coloured to the human eye...
s in photosynthesis
Photosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
. Their cell wall
Cell wall
The cell wall is the tough, usually flexible but sometimes fairly rigid layer that surrounds some types of cells. It is located outside the cell membrane and provides these cells with structural support and protection, and also acts as a filtering mechanism. A major function of the cell wall is to...
s are composed of alginate. They use laminarin
Laminarin
The molecule laminarin is a storage glucan found in brown algae. It is used as a carbohydrate food reserve in the same way that chrysolaminarin is used by phytoplankton. It is created by photosynthesis and is made up of β-glucan with β-linkages. It is a linear polysaccharide, with a β:β ratio...
and mannitol
Mannitol
Mannitol is a white, crystalline organic compound with the formula . This polyol is used as an osmotic diuretic agent and a weak renal vasodilator...
for storage.
Life cycle & growth
Like most brown algae, Postelsia goes through alternation of generationsAlternation of generations
Alternation of generations is a term primarily used in describing the life cycle of plants . A multicellular sporophyte, which is diploid with 2N paired chromosomes , alternates with a multicellular gametophyte, which is haploid with N unpaired chromosomes...
, and is an annual species. The diploid sporophyte produces, through meiosis
Meiosis
Meiosis is a special type of cell division necessary for sexual reproduction. The cells produced by meiosis are gametes or spores. The animals' gametes are called sperm and egg cells....
, haploid spore
Spore
In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...
s, which drip down through the grooves in the blades onto the substrate, which may be mussel
Mussel
The common name mussel is used for members of several families of clams or bivalvia mollusca, from saltwater and freshwater habitats. These groups have in common a shell whose outline is elongated and asymmetrical compared with other edible clams, which are often more or less rounded or oval.The...
s, barnacle
Barnacle
A barnacle is a type of arthropod belonging to infraclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in erosive settings. They are sessile suspension feeders, and have...
s, or bare rock. These spores develop, through mitosis
Mitosis
Mitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets, in two separate nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two cells containing roughly...
, 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
Zygote
A zygote , or zygocyte, is the initial cell formed when two gamete cells are joined by means of sexual reproduction. In multicellular organisms, it is the earliest developmental stage of the embryo...
, which develops into a new sporophyte.
Postelsia are green in color as juveniles, and change to a golden brown as they age, reaching a height of 50 to 75 centimeters.
As a Postelsia alga grows, it's stipe thickens in the same manner as a tree
Tree
A tree is a perennial woody plant. It is most often defined as a woody plant that has many secondary branches supported clear of the ground on a single main stem or trunk with clear apical dominance. A minimum height specification at maturity is cited by some authors, varying from 3 m to...
's trunk. The cells beneath the epidermis
Epidermis (botany)
The epidermis is a single-layered group of cells that covers plants' leaves, flowers, roots and stems. It forms a boundary between the plant and the external environment. The epidermis serves several functions, it protects against water loss, regulates gas exchange, secretes metabolic compounds,...
, called the meristoderm, divide rapidly to form rings of growth, again, like a tree. However, the greater flexibility of Postelsias 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.
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.
Habitat
Sea palms are found on the rocky shores of western North AmericaNorth America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, from as far north as Vancouver Island
Vancouver Island
Vancouver Island is a large island in British Columbia, Canada. It is one of several North American locations named after George Vancouver, the British Royal Navy officer who explored the Pacific Northwest coast of North America between 1791 and 1794...
, to the southern central coast of California. They live in the middle to upper intertidal zones in very wavy areas. High wave action may increase nutrient availability and moves the blades of the thallus, allowing more sunlight to reach the organism so that it can photosynthesize. In addition, the constant wave action removes competitors, such as the mussel
Mussel
The common name mussel is used for members of several families of clams or bivalvia mollusca, from saltwater and freshwater habitats. These groups have in common a shell whose outline is elongated and asymmetrical compared with other edible clams, which are often more or less rounded or oval.The...
species Mytilus californianus. 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. Alternatively, it is thought that the mussels may prevent the growth of competing algae such as Corallina
Corallina
Corallina is a genus of red seaweeds with hard, abrasive calcareous skeletons in the family Corallinaceae. They are stiff, branched plants with articulations.-Species:*Corallina armata J.D.Hooker & Harvey, 1847...
or Halosaccion, allowing Postelsia to grow freely after wave action removes the mussels.
Barnacle
A barnacle is a type of arthropod belonging to infraclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in erosive settings. They are sessile suspension feeders, and have...
s, and rip them from the rocks when the waves come, gripping them with holdfasts of incredible strength.
Epiphytes
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 epiphyticEpiphyte
An epiphyte is a plant that grows upon another plant non-parasitically or sometimes upon some other object , derives its moisture and nutrients from the air and rain and sometimes from debris accumulating around it, and is found in the temperate zone and in the...
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.
Edibility
Meristem
A meristem is the tissue in most plants consisting of undifferentiated cells , found in zones of the plant where growth can take place....
, 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. 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
Royalties
Royalties are usage-based payments made by one party to another for the right to ongoing use of an asset, sometimes an intellectual property...
to the State of California (US$24 per wet ton of algae harvested), and submit a monthly harvest log.
Though some Postelsia harvesters claim their methods of gathering are sustainable, there is no scientific evidence to support these claims. An experiment done to try to prove or disprove such sustainability yielded results stating that recovery from collection depended greatly on the season of collection.