The analysis of biological features of Centaurea cyanus and Agrostemma githago as well as their variability and diversity, depending on the occupied habitats, is presented in the paper. For this purpose, 30 specimens were randomly collected from each studied habitat – stubblefields, winter cereals and spring cereals and put to the morphological analysis with respect of the height of plant, number of ramifications of 1st and 2nd categories, length of the ramifications, number of inflorescences, number of seeds at one plant, a thousand-seed weight and aerial dry mass of plant. The values of features were used for statistic calculations. Centaurea cyanus and Agrostemma githago populations collected in Siedlecka Upland habitats revealed internal variability in respect to all analyzed features. Specimens of Centaurea cyanus differed from each other with regard to the above mentioned features, depending on habitat type. Significant differences between populations occurring in winter cereals, depending on the soil conditions as well as between individuals originating from rye cultivations and stubble-fields in identical soil conditions, were demonstrated. Moreover, no significant differences between populations developing in winter and spring cereals on the analogical soil type were found.
No significant differences between the majority of the investigated features of Agrostemma githago specimens, developing in rye cultivations and in stubble fields in the same soil conditions were noted. There were also no significant differences in features of the studied species between 2005 and 2006 – no interactions between year of studies and habitat type were observed.