There are several points along the path beside the River Tees where bogs have developed on the flat area between the base of Falcon Clints and the river. My eyes were drawn to the bright red hummocks of Sphagnum capillifolium partly from a sense of nostalgia as I did my undergraduate dissertation on this moss and got to learn something of the ecology of the many species of Sphagnum that are found in the British uplands. Many of the species have quite distinct habit preferences, with S. capillifolium being a species that can quite happily live on the dryer parts of the bog. These red hummocks therefore represent a good way of crossing a bog without getting your boots too wet.
A hummock of Sphagnum capillifolium (left) and a handful of Sphagnum cuspidatum (right) from a boggy pool in upper Teesdale.
Today, however, I was more interested in the boggy pools, where, once I had broken the two centimetres of ice with the heel of my boot, I found a different species of Sphagnum, S. cuspidatum, with limp, flaccid stems. I squeezed a handful of stems gently and collected the stream of brown-coloured water into a small sampling vial. Sphagnum is a species that creates its own habitat. The secret lies in the structure of the leaves, whose photosynthetic cells are juxtaposed with empty hyaline cells that, combined with the densely packed stems, allows it to absorb and retain huge quantities of water.
Leaf cells of Sphagnum cuspidatum showing the slender “chlorophyllose” cells (approximately 10 micrometres, or 1/100th of a millimetre wide) between the dead hyaline cells with their thickened bands of supporting tissue.
Under the microscope, this brown liquid yields a rich assortment of algae, mostly diatoms but also a number of cells which share the symmetry which we associate with diatoms but which are larger and are bright green in colour. These are the desmids and they are the only group of freshwater algae that come close to rivaling the diatoms in their diversity. It did not take long to find six distinct species living within the Sphagnum cuspidatum. Look at their structure: each is a single cell mostly divided into two “semi-cells”, each with a separate chloroplast (there are some exceptions to this rule: Netrium [a. in the figure below) does not have semi-cells and a few have a single chloroplast]. The desmids are closely related to Spirogyra which we met in earlier posts from Cassop and the River Ehen.
Desmids from a boggy pool in upper Teesdale. a. Netrium digitus; b. Micrasterias truncata; c) Micrasterias oscitans (var. oscitans); d) Closterium intermedium/striolatum; e) Eurastrum insigne forma; e) Eurastrum didelta. The scale bar is 50 micrometres (1/20th of a millimetre) long.
You can find a lot of information about desmids on the internet. Two sources that are worth exploring are http://www.desmids.nl/index.html which focuses on desmids from the Netherlands but is written in English and has many useful links and http://rbg-web2.rbge.org.uk/DIADIST/ww_intro.htm which has a facsimile of W. and G.S. West’s five volume Flora of British desmids published between 1904 and 1923 which is well worth a look.