Postelsia palmaeformis
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''Postelsia palmaeformis'', also known as the sea palm (not to be confused with the
southern sea palm ''Eisenia arborea'', or the southern sea palm (not to be confused with the sea palm), is a dominant species of kelp that is found on the western Pacific coast of North America, from Vancouver Island, Canada south to Mexico's Isla Magdalena and ...
) or palm seaweed, is a species of
kelp Kelps are large brown algae seaweeds that make up the order Laminariales. There are about 30 different genera. Despite its appearance, kelp is not a plant - it is a heterokont, a completely unrelated group of organisms. Kelp grows in "underwa ...
and classified within
brown algae Brown algae (singular: alga), comprising the class Phaeophyceae, are a large group of multicellular algae, including many seaweeds located in colder waters within the Northern Hemisphere. Brown algae are the major seaweeds of the temperate and p ...
. It is the only known species in the genus Postelsia. The sea palm 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 due to the species' sensitivity to overharvesting.


History

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 Seagrasses are the only flowering plants which grow in marine environments. There are about 60 species of fully marine seagrasses which belong to four families (Posidoniaceae, Zosteraceae, Hydrocharitaceae and Cymodoceaceae), all in the or ...
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 A protist () is any eukaryotic organism (that is, an organism whose cells contain a cell nucleus) that is not an animal, plant, or fungus. While it is likely that protists share a common ancestor (the last eukaryotic common ancestor), the exc ...
s, as well as an example of the class Phaeophyceae.


Etymology

The generic name, ''Postelsia'' honors
Alexander Philipov Postels Alexander Filippovich Postels (russian: Александр Филиппович Постельс; 24 August 1801 Dorpat – 28 June 1871 Vyborg), was a Baltic German of Russian citizenship naturalist, mineralogist and artist. Postels studied at ...
, an Estonian-born geologist and artist who worked with Ruprecht, while the specific name, ''palmaeformis'', describes the alga's superficial similarity in appearance to true
palm Palm most commonly refers to: * Palm of the hand, the central region of the front of the hand * Palm plants, of family Arecaceae **List of Arecaceae genera * Several other plants known as "palm" Palm or Palms may also refer to: Music * Palm (ba ...
s.


Fossil record

Fossils from Monte Bolca, a
lagerstätte A Lagerstätte (, from ''Lager'' 'storage, lair' '' Stätte'' 'place'; plural ''Lagerstätten'') is a sedimentary deposit that exhibits extraordinary fossils with exceptional preservation—sometimes including preserved soft tissues. These f ...
near
Verona Verona ( , ; vec, Verona or ) is a city on the Adige River in Veneto, Italy, with 258,031 inhabitants. It is one of the seven provincial capitals of the region. It is the largest city municipality in the region and the second largest in nor ...
, were originally named ''
Zoophycos ''Zoophycos'' is a somewhat cosmopolitan ichnogenus thought to be produced by moving and feeding polychaete worms. Appearance ''Zoophycos'' occurs in two forms, one planar, and one which resembles a corkscrew. In the latter helicoidal form, ...
caput-medusae'' and previously thought to be
trace fossil A trace fossil, also known as an ichnofossil (; from el, ἴχνος ''ikhnos'' "trace, track"), is a fossil record of biological activity but not the preserved remains of the plant or animal itself. Trace fossils contrast with body fossils, ...
s, but were later found to be plants instead and given the name Algarum by French zoologist Henri Milne-Edwards in 1866. The type specimen collected by Italian
paleobotanist Paleobotany, which is also spelled as palaeobotany, is the branch of botany dealing with the recovery and identification of plant remains from geological contexts, and their use for the biological reconstruction of past environments (paleogeogr ...
Abramo Bartolommeo Massalongo Abramo Bartolommeo Massalongo (13 May 1824 – 25 May 1860) was an Italian paleobotanist and lichenologist. He was born in Tregnago in the Province of Verona and took a great interest in botany as a young man. Massalongo joined the faculty of me ...
before 1855 is at the Natural History Museum of
Verona Verona ( , ; vec, Verona or ) is a city on the Adige River in Veneto, Italy, with 258,031 inhabitants. It is one of the seven provincial capitals of the region. It is the largest city municipality in the region and the second largest in nor ...
and was preserved in a
lithographic limestone Lithographic limestone is hard limestone that is sufficiently fine-grained, homogeneous and defect free to be used for lithography. Geologists use the term "lithographic texture" to refer to a grain size under 1/250 mm. The term "sublith ...
upper and lower slab. When Italian botanist Achille Forti (1878–1937) worked on the specimens in 1926, they were reinterpreted as close relatives of ''Postelsia'', now known to be a
brown algae Brown algae (singular: alga), comprising the class Phaeophyceae, are a large group of multicellular algae, including many seaweeds located in colder waters within the Northern Hemisphere. Brown algae are the major seaweeds of the temperate and p ...
, which had lived in the
coastal waters The coast, also known as the coastline or seashore, is defined as the area where land meets the ocean, or as a line that forms the boundary between the land and the coastline. The Earth has around of coastline. Coasts are important zones in n ...
of the Eocene sea. Forti renamed the species ''Postelsiopsis caput-medusae'' commemorating the fossils' extreme similarity to the extant ''Postelsia palmaeformis''. 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 to . In life, the fronds would have hung vertically whenever the plant was submerged during high tide, and would have flopped over the stipe when the plant was exposed during low tide in a habitus similar to that of the living sea palm. Other specimens from this deposit collected and described by Massalongo in 1855 were actually trace fossils, and they remain assigned to ''Zoophycos''; only the specimens of ''Z. caput-medusae'' have been assigned to ''Postelsiopsis'', as those are fossils of the original plant, and not trace fossils.


Morphology

''Postelsia'' has two distinct morphologies: one for its diploid,
monoicous Monoicy () is a sexual system in haploid plants (mainly bryophytes) where both sperm and eggs are produced on the same gametophyte, in contrast with dioicy, where each gametophyte produces only sperm or eggs but never both.Crandall-Stotler, B.J ...
sporophyte stage, which is the dominant portion of the life cycle, and one for its smaller, haploid, dioecious
gametophyte A gametophyte () is one of the two alternating multicellular phases in the life cycles of plants and algae. It is a haploid multicellular organism that develops from a haploid spore that has one set of chromosomes. The gametophyte is the ...
stage. Like all seaweeds, the sporophyte stage of ''Postelsia'' consists of a
thallus Thallus (plural: thalli), from Latinized Greek (), meaning "a green shoot" or "twig", is the vegetative tissue of some organisms in diverse groups such as algae, fungi, some liverworts, lichens, and the Myxogastria. Many of these organisms ...
, which is made up of a stem-like stipe topped with possibly over 100 leaf-like
blade A blade is the portion of a tool, weapon, or machine with an edge that is designed to puncture, chop, slice or scrape surfaces or materials. Blades are typically made from materials that are harder than those they are to be used on. Histor ...
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 The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away f ...
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 A sporangium (; from Late Latin, ) is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. Virtually all plants, fungi, and many other lineages form sporangia at some point in their life cyc ...
held within these grooves. The gametophyte stage is microscopic, consisting of only a few cells. The gametophytes produce sperm and
eggs Humans and human ancestors have scavenged and eaten animal eggs for millions of years. Humans in Southeast Asia had domesticated chickens and harvested their eggs for food by 1,500 BCE. The most widely consumed eggs are those of fowl, especial ...
to create new sporophytes. Like all phaeophytes, sea palms use the
pigment A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compou ...
s chlorophyll ''a'', chlorophyll ''c'',
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. Fucoxanthin absorbs light primarily in the blue-green ...
, and carotenes in
photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...
. Their cell walls are composed of
alginate Alginic acid, also called algin, is a naturally occurring, edible polysaccharide found in brown algae. It is hydrophilic and forms a viscous gum when hydrated. With metals such as sodium and calcium, its salts are known as alginates. Its colour ...
. They use
laminarin The molecule laminarin (also known as laminaran) is a storage glucan (a polysaccharide of glucose) found in brown algae. It is used as a carbohydrate food reserve in the same way that chrysolaminarin is used by phytoplankton, especially in diato ...
and
mannitol Mannitol is a type of sugar alcohol used as a sweetener and medication. It is used as a low calorie sweetener as it is poorly absorbed by the intestines. As a medication, it is used to decrease pressure in the eyes, as in glaucoma, and to lo ...
for storage.


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 Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately r ...
, 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 gametophytes create sperm and eggs, respectively. The sperm of the male reaches the female egg and fertilizes, resulting in a diploid
zygote A zygote (, ) is a eukaryotic cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individual organism. In multicell ...
, 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 . As a ''Postelsia'' alga grows, its stipe thickens in the same manner as a
tree In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are ...
'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'' 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 America, from as far north as
Vancouver Island Vancouver Island is an island in the northeastern Pacific Ocean and part of the Canadian province of British Columbia. The island is in length, in width at its widest point, and in total area, while are of land. The island is the largest by ...
, to the southern central coast of California. They live in the middle to upper
intertidal The intertidal zone, also known as the foreshore, is the area above water level at low tide and underwater at high tide (in other words, the area within the tidal range). This area can include several types of habitats with various species ...
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 California mussel. 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'' is a genus of red seaweeds with hard, abrasive calcareous skeletons in the family Corallinaceae. They are stiff, branched plants with articulations. Species # '' Corallina aberrans'' (Yendo) K.R.Hind & G.W.Saunders # '' Coralli ...
'' or '' Halosaccion'', allowing ''Postelsia'' to grow freely after wave action removes the mussels. When ''Postelsia'' release their
spores In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, ...
, 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 barnacles, 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
epiphytic An epiphyte is an organism that grows on the surface of a plant and derives its moisture and nutrients from the air, rain, water (in marine environments) or from debris accumulating around it. The plants on which epiphytes grow are called phoroph ...
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

The blades (and less often, the stipes) of ''Postelsia'' are sometimes used in certain dishes, usually in California. ''Postelsia'' is a protected species, however, and harvesting it is illegal throughout much of its range, as clipping the blades too low, below the
meristem The meristem is a type of tissue found in plants. It consists of undifferentiated cells (meristematic cells) capable of cell division. Cells in the meristem can develop into all the other tissues and organs that occur in plants. These cells conti ...
, 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 Overexploitation, also called overharvesting, refers to harvesting a renewable resource to the point of diminishing returns. Continued overexploitation can lead to the destruction of the resource, as it will be unable to replenish. The term ap ...
at some points. It is illegal to harvest ''Postelsia'' in British Columbia, Washington and Oregon. In California, ''Postelsia'' is a partially protected species: recreational harvesting is illegal, but regulated, licensed commercial harvesting is legal. Between 2000 and 2001, an estimated 2 to 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 $100 license, pay a royalty to the State of California ($24 per wet ton of algae harvested), and submit a monthly harvest log. 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.


See also

* Algae *
Brown algae Brown algae (singular: alga), comprising the class Phaeophyceae, are a large group of multicellular algae, including many seaweeds located in colder waters within the Northern Hemisphere. Brown algae are the major seaweeds of the temperate and p ...


References


External links


''Postelsia palmaeformis'' Ruprecht
at AlgaeBase {{Taxonbar, from1=Q18379875, from2=Q3399824 Laminariaceae Flora of the Pacific Marine biota of North America Flora of the West Coast of the United States Flora of California Edible algae Edible seaweeds Laminariales genera Monotypic brown algae genera Flora without expected TNC conservation status