Terrestrial algae in gardens
 
 
The vast majority of algae are found in marine and freshwater environments, but some can be important on land and can be found (if you look for them) in gardens.  They can be grouped into two sets starting with sub-aerial algae which grow open to the air on rocks, buildings and plants.   The other group is soil algae, species found on and within soils. More information about algal groups is found on our pond algae page.
 
Sub-aerial algae
 
Most sub-aerial algae are classed within the cyanobacteria, chlorophyta and diatoms, and they are poorly studied, although more so in some moist tropical countries. They are very common in damp or shaded places, almost always mixed in with mosses and lichens, making a fascinating but unstudied community. These terrestrial algae have evolved structural and physiological strategies to survive desiccation, while others survive by forming resistant spores.1.
 
Algae on rocks and artificial surfaces 
 
Schlichting found 50 species in a study of rock and artificial surfaces in Ireland, including 26 species of cyanobacteria, 17 species of green algae and 5 diatoms.1. The nature of the rock was very important, with different species on bricks or mortar, sandstone or limestone. Chlorella and Chlorococcum,  Pleurococcus were common green algae and Anacystis is a cyanobacterium
 
In the winter, algal films often form on paving slabs and wooden decking, where they can become extremely slippery.  They usually disappear in the dry summer, but if necessary can be removed with a mild power washer. Nature reserves and parks often fit rabbit wire netting over wooden steps to remove danger of injury from slipping.
 
 
 
Green algae growing on a limestone wall and a shaded garden shed.
 
Algae on trees 
 
Tree trunks are often colonised with algae, especially in damp areas and on the shaded north-facing side, and this (also including moss) used to be taught to boy scouts as a way to find compass directions when the sun was hidden.  Desmococcus olivaceus is the abundant sub-aerial chlorophyte alga which forms the powdery green cover commonly seen on tree trunks and other surfaces at the London Natural History Museum (NHM) garden3. Another common tree trunk genus is Trentepohlia which is a filamentous chlorophyte. It has a strong orange colour from abundant carotenoid pigments, and also is a common partner with fungi in forming lichens.
Trentepohlia on tree trunk
Algae in soils
 
Algae of many sorts are very important in soils, where under moist conditions they can sometimes be so abundant as to give a green colour to the soil surface. Because they need sunlight, their abundance declines rapidly deeper in the soil.  Soils are generally moist with films of water around their particles, and so while living on land, many soil algae like Euglena are free-swimming and living in an essentially freshwater environment.
 
Some 38 genera of cyanobacteria and 147 genera of eukaryotic algae are recorded from soil, with numbers generally between 1,000 and 10,000 cells per gram of soil.4. 
 
The cyanobacterial algae such as Nostoc are important nitrogen-fixing organisms, while all algae contribute to primary production through photosynthesis fuelling the soil ecosystem.
 
Soil diatoms are particularly abundant, but poorly studied.  Hantzschia amphioxys and Pinnularia obscura were common in a recent study.5.
 
            Mass of Nostoc or star jelly                                       Diatom Pinnularia species
 
 
Species of the cyanobacterium Nostoc can form substantial and rather revolting jelly-like masses on the surface of soils, especially after rain. Indeed the name Nostoc is derived from the name of the nasal orifice and the mucus it produces.  Common names include star jelly, troll's butter, spit of moon These masses are completely harmless, and the nitrogen-fixing habits of Nostoc make it beneficial in the garden.
 
The soil algae of two 'transplanted' habitats in the NHM Wildlife Garden have been recorded.3. The acidic lowland heath soil was dominated by green algae of several genera including Characium, Chlorococcum, Chlorella and Chlorosarcinopsis, and a diatom Luticola mutica.
 
The alkaline chalk-down soil was dominated by seven sorts of cyanobacteria including species of Anabaena, Chroococcus, Nostoc and Oscillatoria splendida, and another diatom Navicula.
 
An update on the soil algae of the NHM garden was published in 2017, with similar results.6.  It showed that major differences remained in the algae of the two habitat types despite sharing the same climatic conditions for many years.
 
 
References
 
1.  Holzinger A, Karsten U. (2013) Desiccation stress and tolerance in green algae: consequences for ultrastructure, physiological and molecular mechanisms. Front. Plant. Sci. 2013 Aug 22;4:327. https://doi.org/doi: 10.3389/fpls.2013.00327
 
 
2.  Schlichting, H.E.(1975) Some subaerial algae from Ireland, British Phycological Journal, 10: 257-261, htpps://doi.org/10.1080/00071617500650251
 
3.  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
 
4.  Metting, B. The systematics and ecology of soil algae. Bot. Rev 47, 195–312 (1981). https://doi.org/10.1007/BF02868854 
 
5.  Antonellia, M.  et al (2017) On the potential for terrestrial diatom communities and diatom indices to identify anthropic disturbance in soils. Ecological Indicators 75: 73–81
 
6.  Shubert E.  (2017) Comparison of algae inhabiting soils in the wildlife garden to soils of the donor habitat pp. 132-135  In: Further developments of the flora and fauna of the wildlife garden at the Natural History Museum, London: part 2 – twenty one years of species recording. The London Naturalist  no. 96
 
 
Page written and compiled by Steve Head
Terrestrial algae in gardens
 
 
The vast majority of algae are found in marine and freshwater environments, but some can be important on land and can be found (if you look for them) in gardens.  They can be grouped into two sets starting with sub-aerial algae which grow open to the air on rocks, buildings and plants.   The other group is soil algae, species found on and within soils. More information about algal groups is found on our pond algae page.
 
Sub-aerial algae
 
Most sub-aerial algae are classed within the cyanobacteria, chlorophyta and diatoms, and they are poorly studied, although more so in some moist tropical countries. They are very common in damp or shaded places, almost always mixed in with mosses and lichens, making a fascinating but unstudied community. These terrestrial algae have evolved structural and physiological strategies to survive desiccation, while others survive by forming resistant spores.1.
 
Algae on rocks and artificial surfaces 
 
Schlichting found 50 species in a study of rock and artificial surfaces in Ireland, including 26 species of cyanobacteria, 17 species of green algae and 5 diatoms.1. The nature of the rock was very important, with different species on bricks or mortar, sandstone or limestone. Chlorella and Chlorococcum,  Pleurococcus were common green algae and Anacystis is a cyanobacterium
 
In the winter, algal films often form on paving slabs and wooden decking, where they can become extremely slippery.  They usually disappear in the dry summer, but if necessary can be removed with a mild power washer. Nature reserves and parks often fit rabbit wire netting over wooden steps to remove danger of injury from slipping.
 
 
 
Green algae growing on a limestone wall and a shaded garden shed.
 
Algae on trees 
 
Tree trunks are often colonised with algae, especially in damp areas and on the shaded north-facing side, and this (also including moss) used to be taught to boy scouts as a way to find compass directions when the sun was hidden.  Desmococcus olivaceus is the abundant sub-aerial chlorophyte alga which forms the powdery green cover commonly seen on tree trunks and other surfaces at the London Natural History Museum (NHM) garden3. Another common tree trunk genus is Trentepohlia which is a filamentous chlorophyte. It has a strong orange colour from abundant carotenoid pigments, and also is a common partner with fungi in forming lichens.
Trentepohlia on tree trunk
Trentepohlia on tree trunk
Algae in soils
 
Algae of many sorts are very important in soils, where under moist conditions they can sometimes be so abundant as to give a green colour to the soil surface. Because they need sunlight, their abundance declines rapidly deeper in the soil.  Soils are generally moist with films of water around their particles, and so while living on land, many soil algae like Euglena are free-swimming and living in an essentially freshwater environment.
 
Some 38 genera of cyanobacteria and 147 genera of eukaryotic algae are recorded from soil, numbering generally between 1,000 and 10,000 cells per gram of soil.4. 
 
The cyanobacterial algae such as Nostoc are important nitrogen-fixing organisms, while all algae contribute to primary production through photosynthesis fuelling the soil ecosystem.
 
Soil diatoms are particularly abundant, but poorly studied.  Hantzschia amphioxys and Pinnularia obscura were common in a recent study.5.
 
         Mass of Nostoc or star jelly                       Diatom Pinnularia species
 
Species of the cyanobacterium Nostoc can form substantial and rather revolting jelly-like masses on the surface of soils, especially after rain. Indeed the name Nostoc is derived from the name of the nasal orifice and the mucus it produces.  Common names include star jelly, troll's butter, spit of moon These masses are completely harmless, and the nitrogen-fixing habits of Nostoc make it beneficial in the garden.
 
The soil algae of two 'transplanted' habitats in the NHM Wildlife Garden have been recorded.3. The acidic lowland heath soil was dominated by green algae of several genera including Characium, Chlorococcum, Chlorella and Chlorosarcinopsis, and a diatom Luticola mutica.
 
The alkaline chalk-down soil was dominated by seven sorts of cyanobacteria including species of Anabaena, Chroococcus, Nostoc and Oscillatoria splendida, and another diatom Navicula.
 
An update on the soil algae of the NHM garden was published in 2017, with similar results.6.  It showed that major differences remained in the algae of the two habitat types despite sharing the same climatic conditions for many years.
 
 
References
 
1.  Holzinger A, Karsten U. (2013) Desiccation stress and tolerance in green algae: consequences for ultrastructure, physiological and molecular mechanisms. Front. Plant. Sci. 2013 Aug 22;4:327. https://doi.org/doi: 10.3389/fpls.2013.00327
 
 
2.  Schlichting, H.E.(1975) Some subaerial algae from Ireland, British Phycological Journal, 10: 257-261, htpps://doi.org/10.1080/00071617500650251
 
3.  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-
 
4.  Metting, B. The systematics and ecology of soil algae. Bot. Rev 47, 195–312 (1981). https://doi.org/10.1007/BF02868854 
 
5.  Antonellia, M.  et al (2017) On the potential for terrestrial diatom communities and diatom indices to identify anthropic disturbance in soils. Ecological Indicators 75: 73–81
 
6.  Shubert E.  (2017) Comparison of algae inhabiting soils in the wildlife garden to soils of the donor habitat pp. 132-135  In: Further developments of the flora and fauna of the wildlife garden at the Natural History Museum, London: part 2 – twenty one years of species recording. The London Naturalist  no. 96
 
 
Page written and compiled by Steve Head
           Garden Wildplants
        Garden Wildplants