Garden Wildplants

        Garden Wildplants

 

 

The vast majority of garden algal species are found in ponds or streams rather than on land. The UK Centre for Ecology & Hydrology maintains a list of freshwater species recorded in Britain^1. which contains approximately 5,500 species within 14 major botanical groups.  Of these recorded species 446 are in the Cyanobacteria (and the Prochlorophyta) which were once called “blue-green algae” but are in fact photosynthetic bacteria, and not true algae at all.

 

Pond algae are only obvious when they get out of hand and produce blooms or masses of green ropes.  To properly appreciate them you need a compound microscope.  The variety of form and movement of the swimming forms is fascinating, and you will find lots of exciting tiny invertebrates and protozoa in and among your samples.

 

 

Cyanobacteria   424 UK species

 

Cyanobacteria are tiny cells, usually about 25 μm (thousandth of a millimeter) in size, but many join together in groups or chains.  They commonly form mucilaginous encrustations on rocks, and some planktonic species form dangerous “algal” blooms on the surface of warm waters in summer which deplete oxygen and release chemicals toxic to freshwater animals.

 

Oscillatoria is a common pond genus of about 26 species of filamentous form that are often seen covering pond bottoms in autumn.  Anabaena is a free-living genus like a string of beads, while Gleotrichia aggregates to form planktonic colonies like fuzzy balls'

 

 

 

Filaments of Oscillatoria

Strings of Anabaena

Colony of Gleotrichia with a Volvox at top left

 

Pond algae range from minute single-celled swimming cells, to aggregates or chains of similar cells, through to the complex Charophytes that were ancestral to land plants. There are 12 higher taxa or divisions in British freshwater algae, but we will only cover some of the more important ones. The Phaeophyta, or brown algae so dominant in our intertidal seas are represented with only three species in British freshwaters. For convenience we are showing single-celled and simple colonial species together, followed by filamentous species.

 

 

Euglenophyta  175 species

 

The euglinids are a group of tiny single celled or colonial swimming cells which locomote using one or more thin whip-like flagella.  Two very common genera are Euglena, 50-100 μm (42 species) and Phacus (24 species) which are 50μm long with a curious rigid “tail”.  Euglena can become so abundant it can cause green water in ponds.

 

Dinophyta   64 species

 

Commonly known as dinoflagellates, these are very important marine and freshwater planktonic cells, with two flagella arising from grooves, one longitudinal and the other around the “equator” of the cell. This gives them the appearance of having a waist.   They are much more common in the sea, where some species can cause “red tide” blooms, and nocturnal luminescence.  Two common genera are Gymnodinium (10 species) and Peridinium (10 species), mostly less than 50 μm in size.

 

Gymnodinium species

Peridinium species

 

 

 

Chrysophyta 196 species

 

The golden algae have golden-brown pigments and generally two flagella. They are small solitary cells or forming spherical or irregular branching colonies.  Dinobryon (19 species) is about 25 μm, and Synura forms a colonial ball up to 400 μm in diameter.  Dinobryon is found both as single cells and in small tufted colonies.  It can exist by photosynthesis and also more like an animal by engulphing particulate food.

 

                Colony of Dinobryon                                                     Cluster of Synura cells

 

 

Bacillariophyceae  The diatoms 2,046 species

 

These algae are immensely important in the sea and freshwater, accounting for up to half the global annual oxygen production.  They are planktonic and benthic, mostly living as single cells, sometimes forming colonies, which can encrust substrates or other plants.  They lack flagella, and characteristically live inside a silica shell wall in two halves.  The silica shells are beautiful, very intricately patterned and were used to test the quality of microscope lenses. Centric diatoms (182 species) are radially symmetrical like a jellyfish, while pennate diatoms (1,964 species) are bilaterally symmetrical.

 

Stephanodiscus (25 species) is a common planktonic centric diatom up to 60 μm across, and Navicula (340 species) is a boat-shaped genus up to 200 μm long, bottom-living, and able to creep over the substrate using mucilage filaments.

 

                                  Stephanodiscus                                                    Navicula

 

Chlorophyta   2,342 species

 

The chlorophytes or green algae used to be a bit of a rag-bag group of variously related green algae which are physiologically similar to higher plants, but the group is now more restricted.  In garden ponds you can find free-swimming single celled genera such as Chlamydomonas (130 species) and colonial types such as Pandorina (3 species) and Volvox (3 species) with a few to many identical cells in spherical structures. 

 

               Chlamydomonas                                 Pandorina                              Volvox (with daughter colonies)

 

 

Filamentous algae grow into long strands of cells joined end to end.  Many form long straight strings, others are branched or even net-like.

 

Chlorophytes The chlorophytes include some filamentous algae. Oedogonium (74 species) has unbranched multicellular filaments attached to the substrate by a colourless basal holdfast cell. It likes stagnant ponds where it grows either attached or as a gelatinous surface mass. Cladophora is a branching filamentous genus with two freshwater species in Britain, and Cladophora glomerata was the most common mat-forming alga in London’s Natural History Museum ponds.^2. Ulothrix (10 species) is unbranching, with short cylindrical cells at least as broad as they are long.  Hydrodictyon reticulatum is the water-net alga which can make large colonies up to half a metre in width. It forms a mesh like rather than a linear filamentous colony.

 

 

 

 

          Oedogonium strands                        Cladophora glomerata cells and extensive mat of filaments

 

 

Charophytes  More than 1,800 species

 

The Charophytes were once included within the related Chlorophyta,  but now form a separate advanced group which includes the blanket-weed forming Spirogyra (54 species) and Zygnema (18 species).  Both are mucilaginous and slimy to touch and are often detached from the substrate forming masses in the water column and especially at the surface. Spirogyra has spirally arranged chloroplasts, while those of Zygnema are star shaped in pairs in each cell.  They both belong in the Zygnematophyceae which is the sister-group to the land plants.

 

                                Spirogyra                               Zygnema                 Removing blanket-weed from my pond   

 

Charales    Stoneworts  about 40 species

 

Another group of interest within the Charophytes is the stoneworts, which are branching species more complex in overall structure than other green algae, with stems and radiating “branches”.  Their main characteristic is that in  harder waters they tend to secrete calcium carbonate externally, giving them a gritty feeling between the fingers. Stoneworts like clear water with low nutrient status and they tend to be out competed by filamentous algae in most garden ponds.  The only genus likely to be found in a very pure or spring-fed garden pond is Chara of which we have approaching 20 species.

 

Stonewort Chara  It is called "onion-weed" by fishermen in Oxford because it has a garlicky smell.

 

Filamentous algae are usually attached to the pond bottom, stones or other plants, and are an excellent habitat for other algae, and small invertebrates.  It is well worth taking out a small amount of these algae and examining them with a hand lens or microscope and you will see many other algae and animal species using them as a home.

 

They are natural inhabitants of garden ponds but can be unpopular with gardeners when they grow so luxuriantly that they cover the pond surface as blanket weed.  The problem arises from the pond being too rich in plant nutrients, and this is often the case in small garden ponds, especially if they contain fish which are artificially fed.  Blanket weed may appear in spring as the water warms and nutrients from winter-rotted dead plant material is available, but often disappear later.  Proprietary anti-weed products are available, including silica-rich barley straw bales which can help, but the answer is to keep the water as nutrient-free as possible.

 

 

 

1.  Centre for Ecology & Hydrology list of freshwater alga species recorded in Britain

2.  Leigh C. & Ware, C. (2003). The development of the flora, fauna and environment of

the Wildlife Garden at the Natural History Museum, London. Lond. Nat. 82: 75-134

 

 

 

Belcher, H.; Swale, E.. (1976) A beginner's guide to freshwater algae. London, HMSO, 47pp (available as a poor quality download at https://nora.nerc.ac.uk/5209/1/Algae.pdf 

 

Edward G Bellinger and  David C Sigee (2015)  Freshwater Algae Identification, Enumeration and Use as Bioindicators. Wiley-Blackwell 275pp

 

Our How-to guide on managing ponds

 

British Phycological Society  List of professional freshwater algae ID sources

 

 

 

 

The vast majority of garden algal species are found in ponds or streams rather than on land. The UK Centre for Ecology & Hydrology maintains a list of freshwater species recorded in Britain^1. which contains approximately 5,500 species within 14 major botanical groups.  Of these recorded species 446 are in the Cyanobacteria (and the Prochlorophyta) which were once called “blue-green algae” but are in fact photosynthetic bacteria, and not true algae at all.

 

 

 

Cyanobacteria   424 UK species

 

 

Strings of Anabaena

 

 

 

Euglenophyta  175 species

 

 

Dinophyta   64 species

 

 

 

 

 

 

 

           Colony of Dinobryon                           Cluster of Synura cells

 

 

 

 

 

                Stephanodiscus                                               Navicula

 

Chlorophyta   2,342 species

 

 

      Chlamydomonas                      Pandorina       Volvox (with daughter colonies)

 

 

 

Chlorophytes The chlorophytes include some filamentous algae. Oedogonium (74 species) has unbranched multicellular filaments attached to the substrate by a colourless basal holdfast cell. It likes stagnant ponds where it grows either attached or as a gelatinous surface mass. Cladophora is a branching filamentous genus with two freshwater species in Britain, and Cladophora glomerata was the most common mat-forming alga in London’s Natural History Museum ponds.^2. Ulothrix (10 species) is unbranching, with short cylindrical cells at least as broad as they are long.  Hydrodictyon reticulatum is the water-net alga which can make large colonies up to half a metre in width. It forms a mesh like rather than a linear filamentous colony.

 

 

 

 

    Oedogonium strands    Cladophora glomerata cells and extensive mat of filaments

                    Ulothrix                                     Hydrodictyon reticulatum

 

 

 

 

               Spirogyra                   Zygnema          Removing blanket-weed

 

Charales    Stoneworts  about 40 species

 

 

 

 

 

 

 

1.  Centre for Ecology & Hydrology list of freshwater alga species recorded in Britain

 

 

 

Belcher, H.; Swale, E.. (1976) A beginner's guide to freshwater algae. London, HMSO, 47pp (available as a poor quality download at https://nora.nerc.ac.uk/5209/1/Algae.pdf