I made a short diversion back to the car after sampling at Ennerdale’s south-eastern end (see “Reflections from Ennerdale’s Far Side …”) crossing the boggy land behind the gravel spit and dipping into one of the pools to pull out a handful of submerged Sphagnum in the hope of finding some desmids, a group of algae that I have not looked at for some time (see “Swimming with desmids …” for my most recent post on this group).
Squeezing the water from a handful of Sphagnum from a bog pool into a vial and allowing the contents of this water to settle is usually a reliable way of collecting desmids; however, on this occasion the haul was rather meagre. There were plenty of diatoms, but desmids were sparse and limited to a few Pleurotaenium and Euastrum species and some rather impressive cells of Xanthidium armatum.
The distinctive feature of the genus Xanthidium is the bristling armoury of spines around the margins. The arrangement of spines varies between species and X. armatum has one of the most impressive collections, with bundles of three or four short spines at each angle. The photograph below does not really capture the depth of the cell, and it is also not possible to see that there are two “decks” of marginal spines, but also bundles of spines on the top surfaces as well as at the margins. This is truly a man-of-war amongst desmids.
Xanthidium armatum from a boggy pool at the south east end of Ennerdale Water, January 2017. Scale bar: 10 micrometres (= 1/100th of a millimetre). The photographs at the top of this post show the pool from which the sample was collected.
I’m intrigued by desmids but do not claim great competence with the group, so this is a good place to advertise a field meeting organised jointly by the British Phycological Society and the Quekett Microscopical Society. We will be using the Freshwater Biological Association beside Windermere as our base but heading out to various desmid-rich locations in the Lake District over the course of the weekend. There will be opportunities to look at other groups of algae too, but desmids will be the main focus of our weekend. David John of the Natural History Museum will be helping with this group, but there will be experts on other groups available too. If you are interested in coming, let me know and I will keep you informed as the programme evolves.