Ecology and morphology of the freshwater red alga Chroothece in the British Isles

The ecology of Chroothece at six sites in the UK and one in the Isle of Man is de- scribed, together with morphological observations. Sites were near vertical or steep, wetted by trickles and drips, but subject to marked changes in extent of wetting and with parts of the gen- eral area liable to desiccation. Water chemical data are given for four sites, where the alga oc- curred in base-rich, low nutrient waters and with fi lterable organic phosphorus the principal fraction of total fi lterable orthophosphate. Chroothece was associated with a range of cyanobac- teria, especially species of Schizothrix, but also colonial, heterocystous and presumed nitrogen- fi xing genera, and calcicolous diatoms (e.g. Epithemia and Mastogloia). Morphological meas- urements suggest the Chroothece populations all fi t C. richteriana.