Morphological plasticity and ecological range in threeStigeocloniumspecies (Chlorophyceae, Chaetophorales)

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Abstract
Five Stigeoclonium tenue and five S. aestivale strains (both species having wide ecological ranges) and five S. farctum strains (a species with relatively narrow ranges) were examined for chlorine tolerance and morphological plasticity under laboratory conditions. Hair formation, cell dimensions and thallus form were studied. Differentiation in chlorine tolerance was most pronounced in S. aestivale, next in S. tenue and less in S. farctum. For morphological differentiation the sequence was S. tenue, S. farctum and S. aestivale, and for morphological plasticity S. farctum, S. tenue and S. aestivale. It is concluded that in a widespread algal genus such as Stigeoclonium, the ecological ranges are predominantly determined by the degree of ecotypic differentiation, rather than by morphological plasticity. The present study indicates that the separation of S. farctum and S. variabile by Cox & Bold (1966) is not justified and it is suggested that S. variabile may be an ecotype of S. farctum, but to some extent morphological distinct and with different nutritional preferences.