The aim of this study was to investigate the floristic composition and diversity of seven urban habitat types in 24 Serbian cities with different climatic affiliation. In each of the 24 cities, we selected 1 ha plots representing a habitat from one of the following groups: square, boulevard, residential area with compact and with open building pattern, city park, and sites with early and mid-succession vegetation stages. All vascular plant species that occur spontaneously in these plots were observed. Data on the main climatic characteristics were collected for each plot, and data on the life forms were obtained for each species recorded. Diagnostic species were identified for each habitat type analyzed, and alpha, beta and gamma diversity were calculated. A total of 674 taxa were recorded in the studied area. Significant differences were observed in habitats by diagnostic species and by life form representation. The lowest alpha and gamma diversity and the dominance of therophytes were observed in habitat types with intensive anthropogenic impact, whereas the highest number was recorded in mid-successional sites and residential areas with a compact building pattern. The analysis showed that habitat type influences species composition much more than climate.

This study represents the first data gathering and analysis of the floristic composition of ruderal vegetation in Serbia, published over the last 70 years. The dataset included 748 relev?s of ruderal communities and a total of 716 plant species and subspecies. The study showed that the most abundant were widespread taxa, especially taxa of the Eurasian area type, while alien species accounted for a relatively small proportion of the ruderal flora (about 10%). Therophytes and hemicryptophytes were most abundant in the life form spectra. Five vegetation groups were identified, corresponding to the following vegetation classes: Bidentetea, Sisymbrietea, Digitario sanguinalis-Eragrostietea minoris, Artemisietea vulgaris and Polygono-Poetea annuae. The analysis of similarity showed that there are small floristic differences between particular vegetation groups. The determined diagnostic species for the vegetation groups were compared with those of the corresponding anthropogenic vegetation classes, and a high degree of similarity was found for all but one group. The most frequent taxa in all five groups were Polygonum aviculare, Convolvulus arvensis, Plantago major subsp. major and Chenopodium album.

The high diversity of ruderal vegetation in urban environments is well known. Although it has been a subject of numerous studies in Serbia, in recent years it has been slightly overlooked, although, due to the dynamics of ruderal habitats, constant research is required. We investigated ruderal vegetation in 20 cities across Serbia during a period of 5 years. Most of the relevés were collected during the summer months, and within 712 relevés, 422 taxa were recorded. Results of the cluster analyses and identified diagnostic species revealed 26 plant communities, of which nine are dominated or co-dominated by aliens. The relevés can be grouped into six ecologically well-differentiated major vegetation groups. Our study revealed the ruderal communities which are the most widespread in urban environments in Serbia. Additionally, some communities were registered for the first time in the country.

Tokom istraživanja ruderalne vegetacije u gradovima širom Srbije, u tri grada u dolini reke Save zabeležena je nova strana vrsta za floru Srbije, Amaranthus tuberculatus (Amaranthaceae). A. tuberculatus je jednogodišnja biljka poreklom iz Severne Amerike i za sada jedina dvodoma vrsta roda Amaranthus u Srbiji. Naturalizovane populacije su primarno zabeležene u remećenim staništima na obali reke Save u Sremskoj Mitrovici, Šapcu i Beogradu. Vrsta A. tuberculatus je nedavno po prvi put registrovana u dve susedne zemlje, što dodatno ukazuje na širenje areala vrste na Balkanu.