We investigated species composition and relative abundance of Sphagnum fallax dominated peatlands in relation to measured environmental variables on the basis of 26 sites in the Wielkopolska region. Most of studied plots were characterised with soft waters, poor in Ca+ but rich in nutrients, especially N-NH4+ and P-PO43-, with high electrolytic conductivity and high DOC (dissolved organic carbon) concentration. Six out of 19 measured variables of surface water chemistry (DOC, pH, SO42-, P-PO43-, Na+ and Ca2+) explained significantly 23% of the variation in floristic composition. 107 species were observed in 65 vegetation plots. Cluster analysis revealed 4 types of vegetation in studied mires. Sphagnum fallax was the most abundant species and formed plant communities in the wide range of habitats: in the floating mats, with the plants usually adjoining the mineral basin edge (e.g. E. vaginatum, Andromeda polifolia and Ledum palustre) as well as it occupied central parts of Sphagnum lawn (e.g Eriophorum angustifolium) and rich fen habitats (e. g Carex rostrata or Phragmites australis). In Wielkopolska terrestrializating peatlands poor-rich gradient is developed mainly by four variables: conductivity, DOC, SiO2 dissolved, Ca and alkalinity. This study provides a new data on the ecology and typology of Sphagnum peatlands in western Poland.