Ornamental algae

from Wikipedia, the free encyclopedia
Ornamental algae
Micrasterias sp. in the light microscope

Micrasterias sp. in the light microscope

Systematics
without rank: Diaphoreticks
without rank: Archaeplastida
without rank: Chloroplastida
without rank: Charophyta
Class : Ornamental algae (Zygnemophyceae)
Order : Ornamental algae
Scientific name
Desmidiales
CEBessey

The ornamental algae (Desmidiales) together with the yoke algae ( Zygnematales ) form the group of ornamental algae ( Zygnemophyceae ). The latter belong to the derived taxon of the Charophyta , which means that ornamental algae are more closely related to plants than to the actual green algae . The designation ornamental algae is derived from the mostly distinctive morphology of the symmetrical cells with often richly shaped outlines.

construction

The Desmidiales are unicellular algae and can reach sizes of several hundred micrometers. The single cells are rarely glued together to form threads. The cell wall consists of cellulose and can be encrusted (e.g. with iron). A jelly is released through pores in the cell wall , which forms a mucous membrane around the cell. In addition, due to the secretion of mucus, a directed, slow movement on substrate surfaces is possible. The cells consist of two mirror-image halves. Between them a constriction is usually formed equatorially by a sinus, the remaining connection consists of the so-called isthmus ("placoderm desmidia"). The cell nucleus is located in the isthmus. In each half there is a large chloroplast (megaplast), which is often complex and contains pyrenoids . The cells contain vacuoles with crystalline content.

Vegetative propagation

The vegetative reproduction takes place through cell division. After mitosis, the division of the nucleus, the isthmus elongates, the two half-cells dissolve, and the isthmus is constricted. The two halves of the isthmus swell like bubbles to form the missing half-cells, the secondary wall is formed, the typical shape and ornaments are formed. Then the chloroplast of the mother cell penetrates the new half and divides.

Sexual reproduction

Since the ornamental algae, like all representatives of the Zygnemophyceae, have no flagella , sexual reproduction does not take place by means of swarming cells, but by conjugation of two uncultivated cells.

Two genotypically sexually differently determined cells lie next to one another under gelatinous waste. Then the cell walls separate in the middle or a copulation channel is formed between the two partners. The protoplasts of the two unicellular cells meet and combine to form a zygote . This is surrounded by delicate skin. It is initially light and transparent, later dark and opaque due to the accumulation of reserve material. The shell of the zygote is initially smooth, later it develops species-specific spines. The four half-cells stick to the zygote for a long time. The first cell division of the zygote is associated with meiosis . So only the zygote is diploid , so the Desmidiales are haplonts . During the first cell division, a characteristic half of the wall is formed, and cells with the characteristic cell shape only appear after two cell divisions.

Occur

Ornamental algae are almost exclusively inhabitants of fresh water, often in bodies of water with acidic pH values , for example bog pools . They live in plankton , but mostly in benthos and on the submerged parts of plants. Plankton, for example, Cosmarium and Closterium live in eutrophic waters.

Systematics

The closest relatives of the Desmidiales are the yoke algae , with which they form the class of the Zygnemophyceae .

The Desmidiales are a monophyletic group within the Zygnemophyceae. The four families are also likely to be monophyletic:

It is a systematically very well delimited, species-rich group with around 5000 species.

Characteristic genera are:

Individual evidence

  1. ↑ a b c W. Braune, A. Leman, H. Taubert: Plant anatomical internship II . 3rd edition, VEB Gustav Fischer Verlag, Jena 1990, pp. 85-88. ISBN 3-334-00301-9
  2. ^ Karl-Heinz Linne von Berg, Michael Melkonian a. a .: The Kosmos algae guide. The most important freshwater algae under the microscope. Kosmos, Stuttgart 2004, ISBN 3-440-09719-6 , p. 118.
  3. ^ Karl-Heinz Linne von Berg, Michael Melkonian a. a .: The Kosmos algae guide. The most important freshwater algae under the microscope. Kosmos, Stuttgart 2004, ISBN 3-440-09719-6 , p. 122.
  4. ↑ Richard M. McCourt, Kenneth G. Karol, Jeremy Bell, Kathleen M. Helm-Bychowski, Anna Grajewska, Martin F. Wojciechowski, Robert W. Hoshaw: Phylogeny of the conjugating Green Algae (Zygnemophyceae) based on rbcL sequences . In: Journal of Phycology , Volume 36 (4), 200, pp. 747-758. doi : 10.1046 / j.1529-8817.2000.99106.x ; Andrey A. Gontcharov, Birger Marin, Michael Melkonian: Molecular Phylogeny of Conjugating Green Algae (Zygnemophyceae, Streptophyta) Inferred from SSU rDNA Sequence Comparisons . In: Journal of Molecular Evolution , Volume 56, 2002, pp. 89-104. doi : 10.1007 / s00239-002-2383-4
  5. ^ Van den Hoek, C., DG Mann, HM Jahns: Algae: An Introduction to Phycology , Cambridge University Press, Cambridge 1995, p. 468. ISBN 0-521-30419-9

Web links

Commons : Ornamental algae (Desmidiales)  - Collection of images, videos and audio files