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Staurastrum

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Staurastrum
Staurastrum paradoxum
Scientific classification Edit this classification
Clade: Viridiplantae
(unranked): Charophyta
Class: Zygnematophyceae
Order: Desmidiales
Family: Desmidiaceae
Genus: Staurastrum
Meyen ex Ralfs
Type species
Staurastrum paradoxum
Meyen ex Ralfs
Species

See text.

Staurastrum is a large genus of desmids (Desmidiaceae),[1] a group of green algae closely related to the land plants (Embryophyta).[2][3] Members of this genus are microscopic and found in freshwater habitats around the world.

The name Staurastrum comes from the Greek roots stauron, meaning "cross", and astron, meaning "star".[4]

Description

Staurastrum consists of singular cells with two identical halves, called semicells; in most species, the cell is deeply constricted at the middle, making the division between semicells clear. When viewed from the polar axis, they are biradiate (with two planes of symmetry) or pluriradiate (with more than two planes of symmetry).[5] Biradiate individuals have long, arm-shaped extensions (termed "processes") attached to the main body of the semicells. Pluriradiate individuals may lack these processes. The cell wall is either smooth, or covered with granules or spines. In each semicell there is a chloroplast, usually located axially, with radiating lobes and/or ridges; some species have parietally located chloroplasts.[6]

  • Staurastrum saltans, a biradiate species
    Staurastrum saltans, a biradiate species
  • Staurastrum hystrix, a triradiate species
    Staurastrum hystrix, a triradiate species

Identification

Staurastrum as a genus is usually easy to identify, due to its long processes and symmetry. Some smaller species, particularly those without long processes, can be confused with Cosmarium, but that genus has biradiate (not pluriradiate) cells and never with long processes. The smaller species may also be confused with Tetraedron or various xanthophyte algae, but differ in shape, ornamentation, and chloroplast morphology.[5]

Although some species of Staurastrum are unmistakable, identification of species within the genus is often difficult. Important characters for identification include the degree of radiation (the number of planes of symmetry), overall shape and size of the cells, and the distribution and type of ornamentation on the cell wall. As with other genera of desmids, identification is complicated by the fact that these algae exhibit considerable phenotypic variability.[6]

Taxonomy

Staurastrum is the second largest genus of desmids (after Cosmarium), with about 800 species. It is the most heterogeneous desmid genus, and has been described as a wastebin taxon.[7] Several attempts have been made to dismantle the genus and split it up into smaller, more homogeneous units, such as G. M. Palamar-Mordvintseva's segregate genera Cylindriastrum, Cosmoastrum, and Raphidiastrum. These attempts have not been widely accepted, because they are also arbitrary.[8]

Staurastrum is not monophyletic, as molecular phylogenetic studies have shown that members of the genus are dispersed across many clades; however, a "core" Staurastrum clade was resolved.[9] The genus is still in use, because there is no known way of classifying desmids in line with their evolutionary history.[6]

Habitat and distribution

Staurastrum, as well as other desmid genera, live primarily in acidic lakes, ponds, and swamps with low nutrient levels. They usually live on sediments or submerged surfaces. A number of species are characteristic of eutrophic waters and are planktonic.[10]

Many species have a cosmopolitan distribution.[11] However, some species are restricted to a particular biogeographic realm.[12]

Species

References

  1. ^ See the NCBI webpage on Staurastrum. Data extracted from the "NCBI taxonomy resources". National Center for Biotechnology Information. Retrieved 2007-03-19.
  2. ^ Gontcharov AA, Marin BA, Melkonian MA (January 2003). "Molecular phylogeny of conjugating green algae (Zygnemophyceae, Streptophyta) inferred from SSU rDNA sequence comparisons". J. Mol. Evol. 56 (1): 89–104. doi:10.1007/s00239-002-2383-4. PMID 12569426.
  3. ^ See the NCBI webpage on Cosmarium. Data extracted from the "NCBI taxonomy resources". National Center for Biotechnology Information. Retrieved 2007-03-19.
  4. ^ Shayler, Hannah; Siver, Peter A. (2004). "Staurastrum". Carolina Lucid Key to Freshwater Algae. Connecticut College. Retrieved 2024-11-28.
  5. ^ a b Hall, John D.; McCourt, Richard M. (2014). "Chapter 9. Conjugating Green Algae Including Desmids". In Wehr, John D.; Sheath, Robert G.; Kociolek, J. Patrick (eds.). Freshwater Algae of North America: Ecology and Classification (2 ed.). Elsevier Inc. ISBN 978-0-12-385876-4.
  6. ^ a b c Coesel, P.F.M.; Meesters, J. (2013). European flora of the desmid genera Staurastrum and Staurodesmus. Zeist: KNNV Publishing. p. 357. ISBN 978-90-04-27791-5.
  7. ^ Teiling, Einar. "The genus Staurodesmus: A taxonomic study". Arkiv för Botanik. 6 (11): 467–629.
  8. ^ Coesel, P.F.M.; Meesters, K.[J.]. Desmids of the Lowlands. 2nd revised & extended edition. Zeist: KNNV Uitgeverij. p. 424. ISBN 9789050119481.
  9. ^ Gontcharov, Andrey A.; Melkonian, Michael (2005). "Molecular Phylogeny of Staurastrum Meyen ex Ralfs and Related Genera (Zygnematophyceae, Streptophyta) Based On Coding And Noncoding rDNA Sequence Comparisons". Journal of Phycology. 41 (4): 887–899. doi:10.1111/j.0022-3646.2005.04165.x.
  10. ^ Coesel, Peter F. M.; Joosten, Anton M. T. (1996). "Three new planktic Staurastrum taxa (Chlorophyta, Desmidiaceae) from eutrophic water bodies and the significance of microspecies in desmid taxonomy". Algological Studies/Archiv für Hydrobiologie, Supplement Volumes. 80: 9–20. doi:10.1127/algol_stud/80/1996/9.
  11. ^ Gerrath, Joseph F. (2003). "Conjugating Green Algae and Desmids". Freshwater Algae of North America. By Wehr, John D.; Sheath, Robert G. Elsevier Inc.
  12. ^ Coesel, Peter F. M. (1996). "5. Biogeography of desmids". Hydrobiologia. 336 (1–3): 41–53. doi:10.1007/BF00010818. S2CID 11752270.


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