Logo der Sektion Phykologie

Phycology Section

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

Press Release

January 2nd 2012

Algal of the year: The Stoneworts (Chara species) – pioneers and keystone species under threat

Stoneworts belonging to the genus Chara are algae of the year 2012. They were selected by algal researchers of the Phycology Section of the German Botanical Society because members of this genus represent so many different algal life strategies. According to algal expert Dr Irmgard Blindow from the Ernst-Moritz-Arndt-University Greifswald, some Chara species are able to conquer new aquatic habitats as ‘pioneers’ whilst others exhibit very specific growth requirements, and once having colonised an area, can shape an ecosystem. The decision to declare Chara ‘Algae of the year’ acknowledges the importance of this group of algae which comprises 20 native species included in the Red List of threatened species.

Their German name ‘Armleuchteralgen’ (lit. ‘chandelier algae’) refers to the morphology of Chara species (and some other relatives within the family Characeae) which has been likened to candleholders: especially at Christmas time one might be tempted to look for seasonal decorations amongst the whorl-like branches of the algae. The English name for the group (‘stoneworts’) is based on the thick calcium carbonate layers that surround the algae when growing in hard waters.

There are about 300 different Chara species worldwide; most of the species found in Germany live in calcium-rich and nutrient poor lakes, whilst some thrive in brackish water at intermediate salinity. Many Chara species are amongst the first colonisers of newly-formed water bodies but others take longer to become established.  ‘Even though the restoration of a water body may be considered successful with regard to other aspects, this does not automatically mean that Chara can become re-established – even if the genus was present there in the past’ explains Chara expert and ecologist Dr Irmgard Blindow who is based at the Biological Research Station Hiddensee which is part of the University of Greifswald.

Keystone organisms

Once they become re-established, some stoneworts can dominate a whole water body; a good example of this is the Coral Stonewort (Chara tomentosa). This species can form dense underwater ’meadows’ which are valuable nursery grounds for fish. The algae are also an important food source for birds and provide habitats for smaller aquatic animals. Stoneworts can shelter and protect juveniles of many animal species from sit-and-wait predators such as the pike. Because of the essential role they play in ecosystems, biologists refer to such species as keystone organisms.

Birds may contribute to the colonisation of new water bodies; Chara spp. and other stoneworts form robust spores which can survive both freezing and desiccation. These persistent spores, so-called oospores, can also survive the passage through the digestive system of ducks and geese and in this way can be transported to new water bodies.

The spores, which are surrounded by a calcium carbonate layer, allow algal researchers to explore the evolution of the stoneworts. These spores are very persistent compared to the otherwise very soft body of the algae. Their ancestral evolution can be traced back for more than 400 million years to the Devonian period. Some botanists consider the stoneworts the closest relatives of today’s land plants. However recent molecular evidence increasingly suggests that this theory needs to be revised: ‘even if we do not have 100% proof, we now consider the conjugating green algae (Zygnemophyceae) to be the closest relatives, and not the stoneworts’, adds Burkard Becker, Secretary of the Phycology Section.

Threatened species Chara horrida rediscovered

As more and more water bodies are impacted by eutrophication, many Chara species are under threat and included in the Red List of endangered species. In turn, because of the high sensitivity of the stoneworts, biologists can use their presence to assess local water quality. ‘The presence of stoneworts tells us that a water body is more or less healthy’ says Chara expert Blindow. Over the last few decades the introduction of sewage treatment plants has improved water quality in many places so that stonewort populations can recover. One particular species (Chara horrida) which had been declared extinct in Germany in 1980 has recently been rediscovered off the Baltic island of Hiddensee in the Western Pomerania Lagoon Area National Park .


Further information

In some lakes Chara rudis can form underwater meadows

Rediscovered: the species Chara horrida

Orange-red reproductive organs of Chara virgata

Chara tomentosa can dominate lakes

Side branches of Chara hispida are arranged in whorls


The mountain lake ‘Sieben Quellen’ near Sulzbach-Rosenberg in Bavaria, Germany : Chara rudis can form dense meadows and cover the whole bottom of this calcium-rich, nutrient-poor lake.

Photo: © Klaus van de Weyer, lanaplan GbR
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The stonewort Chara horrida had disappeared from German waters in 1980 but has now been rediscovered by algal researchers in the Bodden Waters off the Baltic island of Hiddensee . The alga which can be up to 40 cm in length has so many spines that its main axis is hardly visible (see image below) which has resulted in its descriptive German common name ‘struppig’ which means ‘bristly’ or ‘rugged’.

Photo on top: © Sven Dahlke, Biologische Station Hiddensee, Germany.
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Photo bottom: © Gustav Johansson, Hydrophyta Ekologikonsult, Sweden
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The male reproductive organ (antheridium) of the Delicate Stonewort (Chara virgata) is strikingly orange-coloured. Above this the egg is visible which is surrounded by cells arranged in a helix; once an egg is fertilised, these cells become calcified. In this state the egg can survive heat and desiccation and can be dispersed to new aquatic habitats by ducks, geese and other wildfowl.

Photo: © Gustav Johansson, Hydrophyta Ekologikonsult, Schweden.
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The Coral Stonewort (Chara tomentosa) can dominate the entire bottom of lakes. This stonewort is one of the few species that be identified without a microscope. Even from a distance it can be recognised by its striking orange-red colouration (above). The sheath cells that surround the main axis are twisted in a rope-like fashion and covered in short, thickened spurs (below)

Both images: © Gustav Johansson, Hydrophyta Ekologikonsult, Sweden
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Like in other stoneworts branchlets of the Bristly Stonewort (Chara hispida) are arranged in whorls.

Photo: © Klaus van de Weyer, lanaplan GbR.
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Image rights

Use of the images is only permitted in connection with reporting on the topic ‘alga of the year 2012’ and only if the photographer is acknowledged in the format: first name, second name, institution. Commercial use of the images is not permitted.

Contacts for the media

PD Dr. Irmgard Blindow

The expert for Chara is head of the Biologische Station, University of Greifswald, on the isle of Hiddensee

Tel.: ++49 (0) 38300 - 50251


HD Dr. Burkhard Becker

The Secretary of the Phycology Section researches the evolution of land plants at the University of Cologne, Germany

Tel.: ++49 (0)221-4707022


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 promotes algal research and supports young scientists. 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/pages/01IntroEngl.html

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

Text: Dr. Esther Schwarz-Weig: www.Sci-Stories.com
Translation: Dr. Dagmar Stengel:
National University of Ireland, Galway