Xenococcus
| Generic name: XENOCOCCUS Thuret in Bornet et Thuret, 1880. Notes Algol. 2: 74. | ||||||||||
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| Type species: Xenococcus schousboei Thuret 1875. | ||||||||||
| Descriptions: Komárek & Anagnostidis (1998): Cells attached to the substrate, solitary or in monolayered groups, sometimes forming blastoparenchymatous colonies or a crustose or flat thin thallus with densely arranged cells; young stages characterized usually by discontinuous groups of sessile cells, sometimes with spaces between one another. Cells more or less polarized, sometimes slightly or distinctly elongate along the vertical axis (this polarity is particularly recognizable ill solitary cells). Around cells usually firm, less frequently gelatinous sheaths. Cells in old colonies are sometimes organized into short, horizontal, irregular rows. All cells more or less the same size, at the colonial margin usually rounded or elongate. Komárek (1992): Unicellular - colonial; cells attached to the substrate in one layer, forming flat up to pseudoparenchymatic, circular or elongated in outline colonies; colonies microscopic, later composed from densely agglomerated cells. Cells more or less spherical, subspherical, oval, irregular, polygonal with rounded corners, or slightly pyriform, usually enveloped by colour- less, thin, firm or diffluent, sometimes slightly layered, tight or slightly widened mucilaginous sheaths; cell content blue-green, greyish or reddish. Geitler (1932): Thallus entweder dauernd eine festgewachsene, einschichtige blastoparenchvmatische Scheibe, oder nur in der Jugend scheibenförmig und später durch Bildung aufrechter Fäden mehr oder weniger halbkugelig oder flach krustenförmig, oder aus locker vereinigten Zellen bestehend, dann aber mit meist deutlicher Polarität der Zellen. Aufrechte Fäden, wenn vorhanden, kurz und wenigzellig, anfangs unverzweigt, frühzeitig an den Spitzen dicho- bis tetrachotom verzweigt, seitlich miteinander verwachsen und zu einem scheinbaren parenehymatischen Lager zusammenschließend. Zellen durch schnell aufeinanderfolgende Teilungen oft in Vierer- oder Achtergruppen. Sporangien, wenn vorhanden, in den Scheiben randstendig, in den aufrechten Fäden terminal. Endosporen zu vielen sukzedan gebildet; entleerung der Endosporen durch Aufreissen oder durch verschleimung der Wand. |
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| Genotype differences, molecular data: | ||||||||||
| Reproduction strategies, life cycles, cell division: Komárek & Anagnostidis (1998): Cells divide irregularly in two or more different planes, but usually perpendicular to the substrate; divided cells separate from one another or remain closed in a common sheath. Occasionally in solitary cells occurs successive baeocytic division into numerous baeocytes, which are liberated from the enveloping sheaths by their splitting or gelatinization. The baeocytes differentiate from the whole mother cell, or the cell first divides into two parts by more or less horizontal binary fission and only one (upper) part divides into baeocytes. Komárek (1992): Division of cells irregular, more or less perpendicularly to the substrate; cells do not grow into original shape before the next division. From cells arise sometimes nanocytes, which serve to the reproduction. |
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| Taxonomic position, higher hierarchy: Cyanophyceae, Chroococcales, Xenococcaceae Notes to taxonomy, misinterpretations: About 20 described species, the majority of which need revision. |
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| Ecology, ecophysiology, ecological significance: Komárek (1992): Attached to different substrates (stones, algae, water plants) in different water biotopes; several species are known from mountain streams, other ones from the sea littorals. Several species have probably the special areas of distribution. A little known genus. |
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| List of species: Xenococcus alpinus Emoto et Yoneda 1942 Xenococcus angulatus Setchell et Gardner 1937 Xenococcus bicudoi Montejano et al. 1993 Xenococcus candelariae Tavera et Komárek 1996 Xenococcus chaetomorphae Setchell et Gardner in Gardner 1918 Xenococcus cladophorae (Tilden) Setchell et Gardner 1918 Xenococcus deformans Setchell et Gardner 1924 Xenococcus elenkinii Pohribniak 1937 Xenococcus endophyticus Setchell et Gardner 1937 Xenococcus gaditanus Gonzalez-Guerrero 1947 Xenococcus gilkeyae Setchell et Gardner in Gardner 1918 Xenococcus gracilis Lemmermann 1898 Xenococcus laminariae Feldmann 1953 Xenococcus lammellosus Gold-Morgan et al. 1994 Xenococcus laysanensis Lemmermann 1905 Xenococcus lyngbyeae Jao 1939 Xenococcus minimus Geitler 1922 Xenococcus pallidus (Hansgirg) Komárek et Anagnostidis 1995 Xenococcus pulcher Hollenberg 1939 Xenococcus pyriformis Setchell et Gardner in Gardner 1918 Xenococcus schousboei Thuret 1875 Xenococcus violaceus Anand 1937 Xenococcus willei Gardner 1927 Xenococcus yellowstonensis Copeland 1936 Xenococcus yonedae Umezaki et M. Watanabe 1994 Unclear taxa: |
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Drawings: Komárek 1992
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