Logo der Sektion Phykologie

Phycology Section

of the German Botanical Society (Deutsche Botanische Gesellschaft, DBG, e.V.)

Press Release

4. 8th 2008

Alga of the Year 2008: Micrasterias - immortal but in the Red Data Book for endangered species

Algal researchers of the Phycology Section of the German Botanical Society have chosen the desmid Micrasterias as ‘Alga of the Year 2008’. Micrasterias, the name derived from Greek meaning ‘little star’, is a highly threatened, but species-rich and morphologically extremely diverse, genus of green algae. They entirely depend on the presence of unspoilt freshwater bodies for their existence.

‘The most fascinating feature of Micrasterias algae is their sheer beauty’, enthuses Monika Engels, a phycologist at the University of Hamburg who grows desmids in laboratory cultures. They are more closely related to land plants than to other algae, but their beauty is best appreciated when looking through a microscope: the mostly spherical or disc-shaped unicellular organisms have a very characteristic cell wall and usually consist of two identical, symmetrical compartments which are linked by a narrow connection point or bridge, the so-called isthmus. ‘Some Micrasterias species even have a radial symmetry and therefore even more than just one axis’, explains Engels. Most Micrasterias species are very small, about the diameter of a human hair, between 0.1 und 0.3 millimeter. This means the different types and species can only be distinguished and identified by using a microscope.

Micrasterias indicates clean water

Algae belonging to the genus Micrasterias are commonly used in environmental protection and management as bioindicators: Micrasterias is the most important genus of desmids for indicating water quality because these algae are extremely sensitive and respond to their immediate environment. For example, different species can be found in water bodies with different pH: only very few species can exist in acid waters, however each of these may be present in high numbers. By contrast, many species occur in moderately acidic waters, but usually in only small numbers. Some Micrasterias species occur only in very nutrient-poor waters and can therefore be used to identify unpolluted water bodies.

Survival is uncertain

Most of the nearly 800 groups of desmids that occur in Germany are threatened by extinction. ‘More than 500 species are already listed as endangered in the Red Data Book of endangered species’, says Wolf-Henning Kusber of the Botanical Museum in Berlin-Dahlem, whose job it is to regularly update the list of endangered and threatened species of German desmids. Desmids are under threat because they live in nutrient-poor bogs; due to peat extraction and agricultural development, more and more of our bogs have been lost. Some species of Micrasterias have only been recorded by algal researchers a couple of times after they had initially been described. Several species have been lost already from regions near Hamburg and Berlin . But even in the few remaining bogs the ‘little stars’ have become very rare because nutrients are often washed even into remote boggy areas by rainfall. As the algae are unable to adapt to changing environmental conditions, the only way to protect them is to protect the habitats they live in.

Resistant cell walls

Desmids belonging to the Micrasterias group can either float in open water bodies, live on the bottom of lakes, ponds and streams, or grow on other aquatic plants. Because their cell walls contain a very resistant polymer, Micrasterias species can survive periods of desiccation at the water’s edge, or can, on a trail of mucilage they can excrete, move towards damper areas or water, or towards the light.

Micrasterias is immortal

Sometimes Micrasterias species are described as ‘immortal’ because they can reproduce and multiply by a type of asexual reproduction that works by simple cell division: to reproduce, the two halves of the algae move away from the centre of the cell. After the nucleus (which is located in the isthmus) has been duplicated, the constriction in the centre of the cell extends, the two halves separate, and for each remaining half cell, a new half re-grows. The two new algal cells thus are identical copies of the original organism and each new cell now consists of two halves of different ages, one newly grown, and one derived from the mother cell.

Algal mating

Micrasterias can also reproduce sexually but this is quite rare and this occurs by what is called ‘sexual conjugation’: two differently determined cells arrange themselves under a mucilaginous envelope and connect by means of a conjugation channel. The protoplasts of the two cells merge into a zygote with a very smooth outer surface. For a short time the four half-cells remain connected. As Micrasterias species contain only a single set of chromosomes (haploid), it takes two cell divisions to develop their typical cell walls, which allows them to adopt their characteristic, species-specific shapes. The newly formed young algae now contain re-mixed genetic material derived from the two parent cells, but in a new combination.


Micrasterias furcata has a diameter of only 0.2 millimeters and occurs in boggy areas. It is classified as ‘endangered’ according to the Red Data Book of 2008. Since it was first discovered and described by scientists it has been observed only in three locations in Germany. The species is classified as ‘near threatened’ in Austria. (Image: Dr. Monika Engels, desmid algal collection, University of Hamburg)
High resolution image:
Micrasterias_furcata_1200.jpg (1,0 MB)

A transparent nucleus is visible in the centre of the disc-shaped species Micrasterias radiosa which typically inhabits upland bogs. Also clearly visible are the numerous small round vesicles that store starch (pyrenoids). The species is very rare in Germany and classified as ‘endangered’ because it can not survive in water bodies affected by nutrient-loading. (Image: Dr. Monika Engels, desmid algal collection, University of Hamburg)
High resolution image:
Micrasterias_radiosa_1200.jpg (1,1 MB)

Micrasterias crux-melitensis was first described from the environs of Berlin in the 1830s.The habitats where it was previously found are now part of Inner City Berlin and have lost their value for the potential growth of desmids. The alga has disappeared even from the outskirts of Berlin since the 1930s. It appears to be still more common in the Netherlands. (Image: Dr. Monika Engels, desmid algal collection, University of Hamburg)
High resolution image:
Micrasterias_crux-melitensis.jpg (0,6 MB)

Micrasterias truncata is considered an endangered species in Germany according to the Red Data Book. Its distribution is limited mostly to nutrient-poor, oligotrophic to mesotrophic bogs. It occurs more commonly in the subalpine regions of Germany and the Austrian Alps. In this image the two green chloroplasts located in the two compartments of the cell are visibly lobed. (Image: Dr. Monika Engels, desmid algal collection, University of Hamburg)
High resolution image:
Micrasterias_truncata_1200.jpg (0,5 MB)

Micrasterias ceratofera

Micrasterias ceratofera is a spiky exotic species from south-east Asia, first described in 1985. The species lives on the bottom of tropical water bodies such as lakes and rivers, and sometimes free-floating as plankton. In contrast to most of the Micrasterias species that occur in Germany, Micrasterias ceratofera does not inhabit boggy places and its distribution in the tropics does not appear to be threatened. The alga on this image was originally collected from Indonesia in 1983. It was brought back to Germany and has been growing in culture ever since.  This culture is available for scientific research in the "Sammlung von Conjugaten-Kulturen (SVCK; Culture Collection for Conjugate Algae)’ at the Institut für Allgemeine Botanik at the University of Hamburg. (Image: Dr. Monika Engels, desmid algal collection, University of Hamburg)
High resolution image:
Micrasterias_ceratofera_1200.jpg (1,4 MB)

Image rights

Use of the images is only permitted in connection with reporting on the topic ‘Alga of the Year 2008’ and only if the photographer is acknowledged in the format: first name, second name, institution. If you would like to use the images for any other purpose please contact Dr. Burkhard Becker (for details see below).

Note for publishers

In case of a publication please send a copy to Dr. Burkhard Becker, Botanisches Institut, Universität zu Köln, Gyrhostraße 15, 50931 Köln.
E-mail: media@dbg-phykologie.de

Contacts for the media

Wolf-Henning Kusber
Botanischer Garten und Botanisches Museum Berlin-Dahlem
Freie Universität Berlin
Königin-Luise-Str. 6-8
D-14195 Berlin
Tel.: ++49 (0)30-838-50177
w.h.kusber (at) bgbm.org

Dr. Monika Engels
Abteilung Zellbiologie und Phykologie,
Universität Hamburg,
Ohnhorststr. 18
D-22609 Hamburg
Tel. ++49 (0)40-428 16 321 
E-Mail: engels@botanik.uni-hamburg.de

Further information

Members of the Phycology Section (Algology) conduct research on algae and investigate, amongst others, taxonomical, ecological, physiological and molecular topics on macro- and microalgae. The Section is one of five subject-specific Sections of the German Botanical Society (Deutsche Botanische Gesellschaft (DBG) e.V.).

www Links

Section Phycology: www.dbg-phykologie.de

German Botanical Society (Deutsche Botanische Gesellschaft ,DBG) e. V.:

Text: Dr. Esther Schwarz-Weig: www.WissensWorte.de, translated by Dr. Dagmar Stengel