Abstract
The free-living forms of A. nodosum are discussed and classified. Five distinct forms occur, namely, ecad mackaii (beach form), ecad mackaii (turf form), ecad scorpioides (Baltic form), ecad scorpioides (marsh form) and variety minor. A detailed account is given of the ecad mackaii (beach form) in west Scotland and the factors controlling its occurrence and development are discussed. A description is given of the ecad mackaii (turf form) for which no previous record exists. The variety minor is recorded for west Scotland.