AbstractAxenic culture conditions which supported adequate to relatively rapid growth and development ofSphagnumspecies were used to conduct common garden experiments with two taxa in SectionIsocladusand four in SectionCuspidata. Our main objective was to determine if certain variable taxonomic characters (e.g. hemi-isophylly vs hetrophylly) are‘genetically fixed’or environmentally induced. We found that heterophylly and toothing of branch leaf margins were not‘genetically fixed’in the taxa we investigated. All taxa were isophyllous under uniform growing conditions. Characters that appeared least subject to environmental modulation were general growth habit and histological characters of branch leaves. Under common garden conditions, both taxa in SectionIsocladusremained distinct, but only three of the four taxa in SectionCuspidatadid.