Algae ( or ; singular alga , Latin for "seaweed") 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 distinct organs found in land plants. The largest and most complex marine forms are called seaweeds.
Though the prokaryotic cyanobacteria (commonly referred to as blue-green algae) were traditionally included as "algae" in older textbooks, many modern sources regard this as outdated as they are now considered to be bacteria. The term algae is now restricted to eukaryotic organisms. All true algae therefore have a nucleus enclosed within a membrane and plastids bound in one or more membranes. Algae constitute a paraphyletic and polyphyletic group, as they do not include all the descendants of the last universal ancestor nor do they all descend from a common algal ancestor, although their plastids seem to have a single origin. Diatoms are also examples of algae.
Algae are found in the fossil record dating back to approximately 3 billion years in the Precambrian. They exhibit a wide range of reproductive strategies, from simple, asexual cell division to complex forms of sexual reproduction.
Algae lack the various structures that characterize land plants, such as phyllids (leaves) and rhizoids in nonvascular plants, or leaves, roots, and other organs that are found in tracheophytes (vascular plants). Many are photoautotrophic, although some groups contain members that are mixotrophic, deriving energy both from photosynthesis and uptake of organic carbon either by osmotrophy, myzotrophy, or phagotrophy. Some unicellular species rely entirely on external energy sources and have limited or no photosynthetic apparatus.
Nearly all algae have photosynthetic machinery ultimately derived from the Cyanobacteria, and so produce oxygen as a by-product of photosynthesis, unlike other photosynthetic bacteria such as purple and green sulfur bacteria. Fossilized filamentous algae from the Vindhya basin have been dated back to 1.6 to 1.7 billion years ago.
The ancient Greek word for seaweed was φῦκος (fūkos or phykos), which could mean either the seaweed, probably Red Algae, or a red dye derived from it. The Latinization, fūcus, meant primarily the cosmetic rouge. The etymology is uncertain, but a strong candidate has long been some word related to the Biblical פוך (pūk), "paint" (if not that word itself), a cosmetic eye-shadow used by the ancient Egyptians and other inhabitants of the eastern Mediterranean. It could be any color: black, red, green, blue.
Accordingly the modern study of marine and freshwater algae is called either phycology or algology. The name Fucus appears in a number of taxa. The singular form is alga.
By modern definitions Algae are Eukaryotes and conduct photosynthesis within membrane-bound organelles called chloroplasts. Chloroplasts contain circular DNA and are similar in structure to Cyanobacteria, presumably representing reduced cyanobacterial endosymbionts. The exact nature of the chloroplasts is different among the different lines of Algae, reflecting different endosymbiotic events. The table below describes the composition of the three major groups of Algae. Their lineage relationships are shown in the figure in the upper right. Many of these groups contain some members that are no longer photosynthetic. Some retain plastids, but not chloroplasts, while others have lost plastids entirely. The singular form is alga.
Phylogeny based on plastid. not nucleocytoplasmic genealogy:
|2= |2=Chlorarachniophytes }} }} }} }} }}
! Supergroup affiliation !! Members !! Endosymbiont !! Summary | ||||||||||||||
Primoplantae/Archaeplastida | * Chlorophyta | * Rhodophyta | * Glaucophyta | Cyanobacteria | These Algae have primary chloroplasts, i.e. the chloroplasts are surrounded by two membranes and probably developed through a single endosymbiotic event. The chloroplasts of Red Algae have chlorophylls a and c (often), and phycobilins, while those of Green Algae have chloroplasts with chlorophyll a and b. Higher plants are pigmented similarly to Green Algae and probably developed from them, and thus Chlorophyta is a sister taxon to the plants; sometimes they are grouped as Viridiplantae. | |||||||||
Excavata and Rhizaria | * Chlorarachniophytes | * Euglenids | Green Algae | These groups have green chloroplasts containing chlorophylls a and b. Their chloroplasts are surrounded by four and three membranes, respectively, and were probably retained from ingested Green Algae. |
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Chlorarachniophytes, which belong to the phylum Cercozoa, contain a small nucleomorph, which is a relict of the algae's cell nucleus>nucleus. |
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Euglenids, which belong to the phylum Euglenozoa, live primarily in freshwater and have chloroplasts with only three membranes. It has been suggested that the endosymbiotic Green Algae were acquired through myzocytosis rather than phagocytosis. | ||||||
Chromista and Alveolata | * Heterokonts | * Haptophyta | * Cryptomonads | * Dinoflagellates | Red Algae | These groups have chloroplasts containing chlorophylls a and c, and phycobilins.The shape varies from plant to plant. they may be of discoid, plate-like, reticulate, cup-shaped, spiral or ribbon shaped. They have one or more pyrenoids to preserve protein and starch. The latter chlorophyll type is not known from any prokaryotes or primary chloroplasts, but genetic similarities with the Red Algae suggest a relationship there. |
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In the first three of these groups (Chromista), the chloroplast has four membranes, retaining a nucleomorph in Cryptomonads, and they likely share a common pigmented ancestor, although other evidence casts doubt on whether the Heterokonts, Haptophyta, and Cryptomonads are in fact more closely related to each other than to other groups. |
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dinoflagellate chloroplast has three membranes, but there is considerable diversity in chloroplasts within the group, and it appears there were a number of endosymbiotic events. The Apicomplexa, a group of closely related parasites, also have plastids called apicoplasts. Apicoplasts are not photosynthetic but appear to have a common origin with Dinoflagellates>Dinoflagellate chloroplasts. |
W.H.Harvey (1811—1866) was the first to divide the Algae into four divisions based on their pigmentation. This is the first use of a biochemical criterion in plant systematics. Harvey's four divisions are: Red Algae (Rhodophyta), Brown Algae (Heteromontophyta), Green Algae (Chlorophyta) and Diatomaceae.
Most of the simpler algae are unicellular flagellates or amoeboids, but colonial and non-motile forms have developed independently among several of the groups. Some of the more common organizational levels, more than one of which may occur in the life cycle of a species, are
In three lines even higher levels of organization have been reached, with full tissue differentiation. These are the brown algae,—some of which may reach 50 m in length (kelps)—the red algae, and the green algae. The most complex forms are found among the green algae (see Charales and Charophyta), in a lineage that eventually led to the higher land plants. The point where these non-algal plants begin and algae stop is usually taken to be the presence of reproductive organs with protective cell layers, a characteristic not found in the other alga groups.
Algae of the Dinoflagellate phylum are often endosymbionts in the cells of marine invertebrates, where they accelerate host-cell metabolism by generating immediately available sugar and oxygen through photosynthesis using incident light and the carbon dioxide produced in the host. Endosymbiont algae in the Stony Corals are described by the term zooxanthellae, with the host Stony Corals called on that account hermatypic corals, which although not a taxon are not in healthy condition without their endosymbionts. Zooxanthellae belong almost entirely to the genus Symbiodinium. The loss of Symbiodinium from the host is known as coral bleaching, a condition which unless corrected leads to the deterioration and loss of the reef.
The Algal Collection of the U.S. National Herbarium (located in the National Museum of Natural History) consists of approximately 320,500 dried specimens, which, although not exhaustive (no exhaustive collection exists), gives an idea of the order of magnitude of the number of algal species (that number remains unknown). Estimates vary widely. For example, according to one standard textbook, in the British Isles the UK Biodiversity Steering Group Report estimated there to be 20000 algal species in the UK. Another checklist reports only about 5000 species. Regarding the difference of about 15000 species, the text concludes: "It will require many detailed field surveys before it is possible to provide a reliable estimate of the total number of species ...."
Regional and group estimates have been made as well: 5000—5500 species of Red Algae worldwide, "some 1300 in Australian Seas," 400 seaweed species for the western coastline of South Africa, 669 marine species from California (U.S.A.), 642 in the check-list of Britain and Ireland, and so on, but lacking any scientific basis or reliable sources, these numbers have no more credibility than the British ones mentioned above. Most estimates also omit the microscopic Algae, such as the phytoplankta, entirely.
The spores of fresh-water Algae are dispersed mainly by running water and wind, as well as by living carriers. The bodies of water into which they are transported are chemically selective. Marine spores are spread by currents. Ocean water is temperature selective, resulting in phytogeographic zones, regions and provinces.
To some degree the distribution of Algae is subject to floristic discontinuities caused by geographical features, such as Antarctica, long distances of ocean or general land masses. It is therefore possible to identify species occurring by locality, such as "Pacific Algae" or "North Sea Algae". When they occur out of their localities, it is usually possible to hypothesize a transport mechanism, such as the hulls of ships. For example, Ulva reticulata and Ulva fasciata travelled from the mainland to Hawaii in this manner.
Mapping is possible for select species only: "there are many valid examples of confined distribution patterns." For example, Clathromorphum is an arctic genus and is not mapped far south of there. On the other hand, scientists regard the overall data as insufficient due to the "difficulties of undertaking such studies."
The various sorts of algae play significant roles in aquatic ecology. Microscopic forms that live suspended in the water column (phytoplankton) provide the food base for most marine food chains. In very high densities (algal blooms) these algae may discolor the water and outcompete, poison, or asphyxiate other life forms.
Algae are variously sensitive to different factors, which has made them useful as biological indicators in the Ballantine Scale and its modification.
To be competitive and independent from fluctuating support from (local) policy on the long run, biofuels should equal or beat the cost level of fossil fuels. Here, algae based fuels hold great promise, directly related to the potential to produce more biomass per unit area in a year than any other form of biomass. The break-even point for algae-based biofuels should be within reach in about ten to fifteen years.
This kind of ore they often gather and lay on great heapes, where it heteth and rotteth, and will have a strong and loathsome smell; when being so rotten they cast on the land, as they do their muck, and thereof springeth good corn, especially barley ... After spring-tydes or great rigs of the sea, they fetch it in sacks on horse backes, and carie the same three, four, or five miles, and cast it on the lande, which doth very much better the ground for corn and grass.
Today Algae are used by humans in many ways; for example, as fertilizers, soil conditioners and livestock feed. Aquatic and microscopic species are cultured in clear tanks or ponds and are either harvested or used to treat effluents pumped through the ponds. Algaculture on a large scale is an important type of aquaculture in some places. Maerl is commonly used as a soil conditioner.
Algae are national foods of many nations: The People's Republic of China consumes more than 70 species, including fat choy, a cyanobacterium considered a vegetable; Japan, over 20 species; Ireland, dulse; Chile, cochayuyo. Laver is used to make "laver bread" in Wales where it is known as bara lawr; in Korea, gim; in Japan, nori and aonori. It is also used along the west coast of North America from California to British Columbia, in Hawaii and by the Māori of New Zealand. Sea lettuce and badderlocks are a salad ingredient in Scotland, Ireland, Greenland and Iceland.
thumb|243px|Dulse, a food.The oils from some Algae have high levels of unsaturated fatty acids. For example, Parietochloris incisa is very high in arachidonic acid, where it reaches up to 47% of the triglyceride pool. Some varieties of Algae favored by vegetarianism and veganism contain the long-chain, essential omega-3 fatty acids, Docosahexaenoic acid (DHA) and Eicosapentaenoic acid (EPA), in addition to vitamin B12. The vitamin B12 in algae is not biologically active. Fish oil contains the omega-3 fatty acids, but the original source is algae (microalgae in particular), which are eaten by marine life such as copepods and are passed up the food chain. Algae has emerged in recent years as a popular source of omega-3 fatty acids for vegetarians who cannot get long-chain EPA and DHA from other vegetarian sources such as flaxseed oil, which only contains the short-chain Alpha-Linolenic acid (ALA).
Agricultural Research Service scientists found that 60-90% of nitrogen runoff and 70-100% of phosphorus runoff can be captured from manure effluents using an algal turf scrubber (ATS). Scientists developed the ATS, which are shallow, 100-foot raceways of nylon netting where algae colonies can form, and studied its efficacy for three years. They found that algae can readily be used to reduce the nutrient runoff from agricultural fields and increase the quality of water flowing into rivers, streams, and oceans. The enriched algae itself also can be used as a fertilizer. Researchers collected and dried the nutrient-rich algae from the ATS and studied its potential as an organic fertilizer. They found that cucumber and corn seedlings grew just as well using ATS organic fertilizer as they did with commercial fertilizers.
;Australia
;New Zealand
;Europe
;Arctic
;Greenland
;Faroe Islands .
;Canary Islands
;Morocco
;South Africa
;North America
af:Alg ar:طحالب az:Yosunlar bn:শৈবাল zh-min-nan:Chó-lūi be:Водарасці be-x-old:Водарасьці bs:Alge bg:Водорасли ca:Alga cs:Řasy da:Alge de:Alge et:Vetikad el:Φύκη myv:Ведьбарсей es:Alga eo:Algo eu:Alga fa:جلبک fr:Algue ga:Algaí gv:Algey gl:Alga ko:조류 (수생 생물) hi:शैवाल hr:Alge io:Algo id:Alga is:Þörungar it:Alga he:אצות jv:Ganggang ka:წყალმცენარეები kk:Балдыр sw:Algae ht:Alg la:Alga lv:Aļģes lt:Dumbliai hu:Alga mk:Алги ml:ആൽഗ ms:Alga nl:Algen ja:藻類 no:Alge nn:Alge pl:Glony pt:Alga ro:Algă qu:Laqu ru:Водоросли sah:Ньалбах scn:Àlica simple:Algae sk:Riasa (vodný organizmus) sl:Alge sr:Алге sh:Alge fi:Levä sv:Alger ta:பாசி tt:Суүсемнәр te:శైవలాలు th:สาหร่าย tr:Su yosunları udm:Вубуртчин uk:Водорості ur:طحالب vi:Tảo zh-yue:藻 zh:藻類
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