Oedogonium is a genus of filamentous, free-living green algae. It was first described in 1820 by Johann Heinrich Friedrich Link, and later given its name by German scientist K. E. Hirn.
The morphology of Oedogonium is unique, with an interior and exterior that function differently from one another and change throughout its life cycle. These algae reside in freshwater ecosystems in both hemispheres and are both benthic and planktonic in nature.Mrozińska T. 1958. Kilka nowych dla Polski i interesujących gatunków z rodzaju Oedogonium. Fragm. Flor. Geobot. Volume 4, 1,2: 247-259.Mrozińska-Webb T. 1976. A study on epiphytic alga of the order Oedogoniales on the basis of materials from Southern Poland. Fragm. Flor. Geobot. Volume 22, 1,2:147-227.Mrozińska T. 1981. Some species of Oedogonium New to Poland. Supplement to “Flora Polska, Oedogoniales, Chlorophyta”. Fragm. Flor. Geobot. Volume 27, 4: 677-680.Mrozińska T. 1984. Flora Polski: Zielenice (Chlorophyta) Edogoniowce (Oedogoniales), PWN, WarszawaKraków. They form algal patches on the water's surface and so interact closely with a multitude of other algae.Khanum, A. 1982: An ecological study of freshwater algal mats. Botany. Bull. Academia Sinica. Issue 1, 23:89-104. These filamentous cells' life cycles include both sexual and asexual reproduction, depending on the life cycle stage.
Although quite common, Oedogonium is difficult to identify to species since key definitive markers are only present during reproduction, which is an uncommon life stage among this genus.David, M.J. 2003: Freshwater Algae of North America. Ecology and Classification; Aquatic Ecology. Volume 1, 311-352. Oedogonium has been found to be important in the fixation of heavy metals in freshwater ecosystems.Gupta, V.K. and Rastogi, A. 2008: Biosorption of lead(II) from aqueous solutions by non-living algal biomass Oedogonium sp. and Nostoc sp.—A comparative study. Journal of Hazardous Materials. Volume 64, 2:170-178.Gupta, V.K. and Rastogi, A. 2009: Biosorption of hexavalent chromium by raw and acid-treated green alga Oedogonium hatei from aqueous solutions. Journal of Hazardous Materials. Volume 163, 1:396-402.
Etymology First named Oedogoniaceen (in German), the name Oedogoniales is derived from the Latin oedos (meaning swelling or tumor) and gonos (meaning offspring or seed). This name describes the morphology that Hirn witnessed during Oedogonium sexual and asexual reproduction and later described in his publication, “Monographie und iconographie der Oedogoniaceen."Hirn, K.E. 1900: Monographie und iconographie der Oedogoniaceen. Acta Societatis Scientiarum Fennicae 27. Volume 1, 24:1-394.
Discovery
Oedogonium species were first reported in the late 19th century by Hilse (1860),Hilse, W. 1860: Beitraege zur Algen – und Diatomeen-Kunde Schlesiens, insbesondere Strehlens. Jahresber. Schles. Ges vaterl. Cult. 38:75-86. Gołowin (1964),Gołowin, S. 1964: Glony torfowisk Chlebowo (pow. Oborniki, woj. poznańskie). Fragm. Florist. Geobot. Volume 10, 1:121-169. Kirchner (1878),Kirchner, O. 1878: Kryptogamenflora von Schlesien. Jahresber. Schles. Ges. Vaterl. Cult. 2,1:3-284. Kozłowski (1895)Kozłowski, W. 1895: Przyczynek do flory wodorostów okolic Warszawy. Pamiętn. Fizjogr. 13:63-73. and Gutwiński (1897).Gutwiński, R. 1897: Wykaz glonów zebranych z okolic Wadowic-Makowa. Spraw. Komis. Fizjogr. AU 32:97-217. Mrozińska was the first to examine the genus in terms of morphology, ecology and distribution and described more than 400 species, mainly from southern Poland.
In 1900, Hirn wrote a monograph concerning his finding of a new taxon, to which he gave the name Oedogoniaceen. Hirn's monograph now serves as the starting point of nomenclature for the family Oedogoniaceae, an exception to Linnaeus' Species plantarum as a starting point for other algae.
In 1991, a paper by Mrozińska presented a new taxonomic classification of the genus Oedogonium, and a proposed division into two sections: I. Monospermatozoideae and II. Dispermatozoideae. These sections were based on the different number of spermatozoids the antheridial (male sex organ containing) cell expresses. This classification is not widely accepted.
Morphology Exterior Cells of the genus Oedogonium are narrow and cylindrical in shape. The algal body consists of green, un-branched, multi-cellular filaments, arranged end to end. Every cell of the filamentous algal body (called the thallus) is similar in shape apart from the apical cell (the uppermost) and the holdfast cell (the lowermost). The apical cell is wider and rounded at its tip relative to the other cells of the thallus. The holdfast cell produces elongated growths from both unattached sides which aid in firmly attaching the filament to a substrate.Guiry, M.D., Guiry, G.M. 2008: AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org; searched on 13 February 2019. The holdfast is also the only colorless cell of the filament.
All other cells in the filament exist as green structures very similar in nature, with only some cells having caps. The number of caps per cell illustrates the number of times that cell has divided. Every cell of the filament has a cell wall consisting of three layers – the innermost is made of cellulose, the middle of pectose, and the outermost is made of chitin, all three of which provide rigidity and protection. Most cells are attached to the substrate by the holdfast and are vegetative cells, although some are free-floating.
Species of Oedogonium are divided into two major groups based on distribution of the sex organs: macrandous and nannandrous species. Macrandous species have a male sex organ (the antheridia) and female sex organ (the oogonia) produced on filaments of normal size. This group is further subdivided into macrandous monoecious and macrandous dioecious. In macrandous monoecious species, the antheridia and oogonia are always found on the same filament. In macrandous dioecious species, the antheridia and oogonia are produced on different filaments. Although filaments bearing antheridia and oogonia are morphologically similar, they differ physiologically. In nannandrous species, filaments producing antheridia and oogonia show morphological distinction. The antheridia, which are much smaller than the oogonia, are called dwarf males. Nannandrous species are always dioecious, i.e., antheridia and oogonia are always produced on different filaments. Small male filaments are likely to be attached to a female filament, near an oogonium.
Interior The protoplasm of Oedogonium is contained by a plasma membrane, and consists of a single nucleus, reticulate chloroplasts, cytoplasm and a central vacuole. Cell sap (contained by the central vacuole) is made up of inorganic compounds, excretions and secretions. Between the innermost cell wall and the central vacuole is a thin layer known as the protoplast. The single nucleus is large, oval shaped, and sits in the centre of the cell, usually touching the membrane and internal to the chloroplast. This large nucleus contains 1-2 nucleoli and elongated chromosomes. The reticulate, parietal chloroplast extends over the whole interior of the cell, enveloping the protoplast. Whether these networked strands are narrow or broad varies between species, but with most species these reticula are parallel to the long axis of the cell. At the strand junctions are pyrenoids, covered in starch plates. Cells of Oedogonium also contain Golgi bodies, mitochondria, and endoplasmic reticulum.
Habitat and ecology Oedogonium resides in freshwater ecosystems and prefers stagnant waters, such as small ponds, pools, roadside ditches, marshes, lakes, and reservoirs. It grows over a large pH range (7.3-9.6) and displays a wide tolerance to variation in nutrient type and amount in water. Cells are either fastened to substrate at the bottom of the water system, or free-floating within. When free-floating they form polyalgal patches (mats) on the water's surface to establish a relatively static habitat, created by interweaving multiple different algal filaments suspended in a gelatinous matrix. This matrix is a result of secretions by free floating thalli.
Oedogonium filaments typically appear during the warmer months, appearing at the end of June (northern hemisphere), and throughout July and August are found prevalent in polyalgal mats.Messyasz, B., Pikosz, M., Schroeder, G., Łęska, B. & Fabrowska, J. 2015: Identification and Ecology of Macroalgae Species Existing in Poland. Chapter 2, In: S.K. Kim & K. Chojnacka (eds.). Marine Algae Extracts: Processes, Products and Application. Mats formed by Oedogonium are multi-species, associated with Spirogyra, Rhizoclonium, and Cladophora. Together these species use holdfast cells to grip one another in order to photosynthesize, forming an algal bloom.
Life cycle Asexual reproduction Oedogonium can reproduce asexually by fragmentation of their filaments, germination of aplanospores and akinetes, and through zoospores. In fragmentation, the filament splits apart and each fragment reproduces to form a fully functioning thallus. Splitting can occur more than once at the same position of the filament. The splitting of fragmentation may or may not be intentional – it can occur due to natural damage by the environment or predators.
Asexual reproduction via zoospore is also very common and occurs in vegetative (benthic) cells. Vegetative cells produce zoosporangia – the enclosure in which spores are formed – which give rise to the zoospores. Each zoospore has a small hyaline anterior region, and at the base of this region is a ring of flagella (~150). Once emerged from the zoosporangium, a zoospore is still enveloped by a fragile vesicle, from which it is soon discharged. Following dispersal, the zoospore experiences a short period of motility in which it searches for a substrate. When attached to a substrate, the ring of flagella is lost, and the zoospore begins dividing to form a new filament.
Germination of aplanospores and akinetes is uncommon but possible. An aplanospore is non-motile and formed within a vegetative cell, the wall of which is distinct from that of the parent cell. Under certain unfavorable conditions, aplanospores will secrete thick walls around them and store abundant food reserves. An akinete spore is large, non-motile, and thick walled, the wall of which is fused to that of the parent cell. Akinetes thick cell walls are enriched in food materials. Both aplanospores and akinetes are able to withstand unfavorable habitual conditions (cold, winter months or nutrient poor waters) and remain dormant under these conditions. With the onset of favorable conditions (such as warm winter months), they can germinate to form a new individual.
Sexual reproduction Sexual reproduction in Oedogonium is oogamous; and can be monoecious or dioecious. Species may either be macrandrous (lacking dwarf males) or nannandrous (possessing dwarf males). Dwarf males are small, short, antheridium-producing filaments attached near the oogonia (female sex organ). These dwarf males are derived from repeated cell division of multi-flagellate androspores. When an oogonial mother cell divides, it forms a swollen oogonium bound by a supporting cell. Oogonial cells may exist in a series along the filament, and so division may also occur in a series; resulting in each oogonium containing a single egg. Production of an egg causes swelling of the cell wall.