Ecological factors relating to morphological variation in the aquatic

Many species of aquatic moss are morphologically very variable (Warnstorf et al. , 1914; Watson, 1919; Lodge, 1959) and recent taxonomic works (Smith, 1978, Crum & Anderson, 1981; Ireland, 1982) give examples where confusion may result from such variability. During the course of a study of metal accumulation by field populations of Rhynchostegium riparioides (Wehr & Whitton, 1983a, b) it became evident that this species exhibits a wide range of morphologies in different types of lotic habitat. The present study was planned to run in parallel with that on metal accumulation because, at least in Northern Europe, R. riparioides is perhaps the most useful of all species for monitoring heavy metal pollution in rivers. The principal objectives were to reveal the extent of morphological variation, to identify those characters which were stable over a broad range of ecological conditions and to determine which environmental factors might be related to the variability. R. riparioides is one of the most common aquatic mosses in rivers in Europe (Nyholm, 1954-1969; Smith, 1978; Watson, 1981) and perhaps also some other temperate regions (Smith, 1978). It tolerates a wide variety of ecological conditions (Watson, 1919; Empain, 1978) and was present in 68.1 % of 1055 one kilometre lengths of river surveyed in England, Scotland and Wales by N. T. H. Holmes (personal communication). The ecology of the species is reviewed in more detail by Wehr & Whitton (1983a).