A several-year study of distribution, phytocoenological differentiation, floristic 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 vegetation often develops, consisting predominantly of annual plants of Sisymbrion officinalis R.Tx., Lohm. et Prsg.1950.
Four species of the Helianthus genus have been found in the non-arable and arable communities in Vojvodina and Serbia, namely: H. annuus, H. tuberosus, H. decapetalus and H. scaberimus. Studies conducted hitherto have shown that Helianthus annuus has the highest frequency in all weed phytocoenoses examined so far. The spreading of H. decapetalus and H. scaberimus, introduced to Vojvodina from the neighboring Hungary and Romania,has still not assumed alarming proportions in quantitative terms, but a tendency has been observed of their further spreading. It is therefore necessary to monitor and study the trend of their expansion over the coming period.
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