A several-year study of distribution, phytocoenological differentiation, flo ristic composition and structure of ruderal flora and vegetation and relevant anthropogenic influence was conducted at Pančevački Rit in Serbia. Ten clearly distinctive ruderal communities were identified in the study, including the newly formed community Matricario-Helianthetum annuae. This community is a unique combination of transitional ruderal and agrestal vegetation developing spontaneously in close vicinity of intensively cultivated agricultural fields, in which sunflower (Helianthus annuus L.), an annual crop, appears and persists subspontaneously and often massively, rendering a physiognomical character to ruderal habitats in which ephemeral ruderal weed veg etation often develops, consisting predominantly of annual plants of Sisymbrion officinalis R.Tx., Lohm. et Prsg.1950.