Desmids on sphagnum moss. Darkfield illuminated polarised light micrograph of Hyalotheca sp. (long, centre) and Desmidium swartzii (long, upper centre) desmids amongst Sphagnum sp. moss leaves (colourful, background). Desmids are a common group of freshwater single-celled algae that have intricate cell walls. Magnification: x100 when printed 10 centimetres wide.