Within-species variation among populations of the <italic>Carex flava</italic> complex as a function of habitat conditions.

<bold><italic>Background</italic></bold>: Variable habitat conditions contribute to morphological variability that plays a substantial part in evolution of plants. Understanding the extent of phenotypic plasticity has important implication for assigning individuals to taxa. <bold><italic>Aims</italic></bold>: I analysed morphological variability among populations within species of the <italic>Carex flava</italic> group and tested to what extent morphological variability was associated with habitat conditions. <bold><italic>Methods</italic></bold>: A total of 571 specimens from 20 populations of four species from the <italic>C. flava</italic> complex were sampled in Poland and tested by Discriminant Function Analysis (DFA). The relationship between morphological characters and habitat factors was explored by means of the redundancy analysis (RDA). <bold><italic>Results</italic></bold>: Variability of the generative and vegetative traits was fairly similar in <italic>Carex lepidocarpa, C. flava</italic> and <italic>Carex demissa</italic>, while it was somewhat higher in <italic>Carex viridula</italic>. The morphological traits were mostly related to soil organic matter content, calcium and carbonate, as well as to habitat fertility (C:N ratio), elevation and habitat disturbance. The results obtained do not support the separation of <italic>C</italic>. <italic>viridula</italic> var. <italic>pulchella</italic> from <italic>C. viridula</italic> var. <italic>viridula</italic>. <bold><italic>Conclusions</italic></bold>: Phenotypic variability in the species of the <italic>C. flava</italic> complex is related to habitat conditions and this can lead to the differentiation of morphotypes within species. [ABSTRACT FROM AUTHOR]