The formation of weed communities in agricultural crops is determined by habitat conditions, soil fertility, and agricultural practice deployed. A multi-year experi- ment evaluated the species composition, the number and air-dry weight of weeds in winter wheat, the horizontal (layered) distribution of weeds in the canopy as well as values of Shannon–Wiener’s diversity index and Sørensen’s similarity coefficient in a weed community. Winter wheat was sown in a crop rotation: potato – winter wheat – peas – winter durum wheat and in a 33–35-year monoculture. Weed infestation indices were evaluated at the tillering stage and the milk maturity stage of winter wheat. At both developmental stages of winter wheat, an almost 3-fold higher number of weeds was recorded in the monoculture than in the crop rotation. Also, the air-dry weight of weeds was higher in the monoculture than in the crop rotation at both developmental stages compared. Weeds of the upper and middle levels accounted for 82–92.3% of the weed community in the crop rotation and for 98.5–100% in the monoculture. A higher value of the Shannon–Wiener’s biodiversity index was computed for the weed community from the crop rotation than from the monoculture. In turn, the Sørensen’s similarity coefficient of the weed community reached 70–76% at the tillering stage and 68–78% at the milk maturity stage of winter wheat.