Floristic diversity in the Pannonian Plain is the result of mosaic habitat composition, characterized by steppes, saline meadows, and lowland forests along major rivers. In the last few centuries, the flora has become enriched by species introduced by human activities, such as colonization and industrialization. Presently it consists of nearly 1800 species. As a result of 30 years of field research as well as herbarium and literature searches, a list of invasive alien neophytes has been compiled and is presented here. The list includes 152 species, classified as either naturalized, casual, or unknown. One of the species is listed in Red Book of Serbian Flora. Eighty species are naturalized, and 61 are casual species. The majority of the introduced flora originates from North America (66) and the Old World (43). Most alien invasive species of the Southeastern part of the Pannonian Plain, were introduced accidentally by seed material or deliberately by nursery saplings. The annual and perennial herbaceous plants, which flower in the summer and summer-autumn periods, are represented in the greatest numbers. The alien flora was further analyzed with respect to taxonomy, life forms, pollination, and seed dispersal mode. The greatest number of alien species appears in anthropogenic and semi-natural habitats (59). In natural habitats, 45 invasive taxa were recorded, representing a conservation threat to biodiversity.

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literature records for four autochthonous and one allochthonous plant in the flora of Serbia has been done. Four plant taxa are a novelty for proper Serbia, Vojvodina, or Kosovo and Metohija, and for 7 plants, presence in certain administrative units in Serbia has been confirmed. In the last part of the paper, there is a review of 9 disputed taxa for our country.

Comparative morphological taxonomic analysis was conducted on two populations of Dactylorhiza maculata (L.) So? 1962 and one population of D. majalis (Reichenb.) P. F. Hunt et Summerhayes 1965 from the area of Stara planina mountain in order to determine new characters that could be used to distinguish these two species and characters that could eventually be used for defining infraspecific taxa within these species. Taxonomic studies have included processing of quantitative and qualitative characters. A total of 60 characters were analyzed, out of which 34 quantitative and 26 qualitative. Analysis of quantitative and qualitative characters included 90 specimens - 60 of D. maculata and 30 of D. majalis. Based on the results obtained by multivariate statistical analysis and literature data, we selected sets of taxonomic characters that allow a clear differentiation of infraspecific forms within the species D. maculata, which is characterized by intensive variability on the selected localities on Stara planina.

During floristic investigations of Serbia, Montenegro and North Macedonia from 2011-2018, orchid specimens from the genus Anacamptis, possible hybrids, with characteristics intermediary to species already described for these countries, were discovered. These specimens, together with all potential parent species, were subjected to morphometric analysis in order to determine their hybrid status and characters that distinguished hybrids from parent taxa. Taxonomic studies have included the processing of quantitative and qualitative characters. A total of 60 characters were analyzed, of which 45 quantitative and 15 qualitative. Analysis of quantitative and qualitative characters included 82 specimens-60 parents and 22 hybrids. Statistical analyses included descriptive and discriminate statistics and multivariate analyses. Hybrid specimens in general had intermediate values of measured characters with different degrees of similarity with one of the parent species. On the other hand, they have higher mean values of some floral characters that may have an evolutionary potential. The possible taxonomic importance of hybrid characters is discussed. Results confirmed that the analyzed specimens are natural orchid hybrids (A. × parvifolia, A. × timbali and A. × gennarii) and represent new plant taxa for the flora of investigated countries.