Green algae belonging to the order Prasiolales have been reported frequently in terrestrial, freshwater, and marine habitats, generally in situations in which they are not submerged continuously and often in association with deposits of avian feces or other rich sources of nitrogenous compounds. Terrestrial habitats in Galway City on the west coast of Ireland have large populations of four such algae: Rosenvingiella polyrhiza (Rosenvinge) P. C. Silva, Prasiola calophylla (Carmichael ex Greville) Kützing, P. crispa (Lightfoot) Kützing, and P. stipitata Suhr ex Jessen, of which only the last is in any way fully associated with a tidal regime. The other species are found in an extraordinary range of nonmarine terrestrial habitats in the center of Galway, a city that still retains its narrow, medieval street plan. Width of the streets, proportion of residences, substratum type, and aspect are shown to be the main factors affecting the distribution of these algae, although a combination of consistent dampness and nitrogenous-compound availability from animal wastes is likely to be the primary determining factor. Morphological and phenological data are presented for each entity, and it is concluded from field observations that R. polyrhiza should continue to be recognized as a separate entity, even though a close relationship with Schizogonium murale Kützing is probable.