Source and transformations of lignin in Carex-dominated peat

► Analytical pyrolysis was applied to plant species and different peat OM fractions. ► The lignin composition of graminoids differed according to preferential habitat. ► Non-lignin phenolic monomers highly contribute guaiacyl moieties in graminoids. ► Several decomposition stages were recognized with factor analysis in the peat OM. ► Their effects on the lignin-carbohydrate complex are discussed.