The class Bidentetea tripartiti R. Tüxen et al. ex von Rochow 1951 encompasses nitrophilic vegetation found in humid areas (swamps, water shores, humid microdepressions) and slightly humid arable land. These associations present a pioneer character, frequently occur in stripe or patches and are mainly made up of annual hygrophytes. In the Romanian Banat, two associations are frequent: Bidenti-Polygonetum hydropiperi Lohmeyer in R. Tüxen 1950 and Echinochloo-Polygonetum lapathifolii Soó et Csűrös 1974. These weed formations appear alongside rivers and lakes banks or in periodically flooded depressions, on soils rich in nutrients, described, among others, by GRIGORE, 1971 (the Timiș-Bega interfluve), COSTE, 1974 (Locva Mountains), OPREA et al., 1974, OPREA, 1976 (Satchinez, Sînnicolaul Mare Plain), LOVASZ, 1995 (Buziaș Plain), DRĂGULESCU, 2013 (Timiș river basin). Our previous research (NEACȘU, 2008) refers to the association Bidenti-Polygonetum hydropiperi Lohmeyer in R. Tüxen 1950 which we studied in two locations: Pișchia (at 123 m altitude) and Surduc (at 196 - 198 m altitudes). The total species number in this composition is of 57. The species average / relevé is of 10.1, the minimum number species / relevé of 5, and the maximum species number / relevé, of 20. Of the species characteristic to the association, cited in the specialty literature and occuring in the flora composition of our phytocenoses, we mention the following: Bidens tripartita L., Polygonum hydropiper L., Echinochloa crus-galli (L.) Beauv., Polygonum mite Schrank, Potentilla reptans L., Alisma plantago-aquatica L., Lycopus europaeus L., Lysimachia vulgaris L., Xanthium strumarium L. Under a synecological aspect, the association is meso-hygrophilic. The ecologic indices analysis shows that the phytocenoses we analysed encompass a higher percentage of mesophilic species, 28.07 %. Their presence is due to the drier aspect of the stations (land in the process of draining) and the community transitory character. The mesophilic species are followed by meso-hygrophilic ones, with 21.52 %, the other categories not being so well represented. The Echinochloo-Polygonetum lapathifolii Soó et Csűrös 1974 phytocenoses, which we studied, can be found at altitudes ranging from 116 m (Pișchia) to 196 m (Surduc). The total number of species identified there is of 24. The average species / relevé is of 9.66, the minimum species number / relevé of 7, and the maximum species number / relevé, of 10. The dominant characteristic species, Echinochloa crus-galli (L.) Beauv., accompanied by Polygonum lapathifolium L. occurs alongside other species characteristic for the association, such as: Rorippa austriaca (L.) Besser., Bidens tripartita L., Pulicaria vulgaris Gaertner, Mentha pulegium L. The last two species indicate a slightly soil salinization tendency. Under the flora composition, life forms and phytogeographic categories aspect, our phytocenoses mostly resemble to those described in the Timiș-Bega interfluve (Timiș county), by GRIGORE (1971), varying to a certain degree from those analysed by COSTE (1974), at Zăvoi and Pojejena (Caraș county), which encompass, aside from characteristic species, a significant number of transgressive species from Isoëto-Nanojuncetea Br.-Bl. et Tx. 1943 and Chenopodietea Oberd. 1957 em. Lohm. et Tx. 1961. This fact is due to the difference in altitude and biotope described by this author (fallows, gardens and humid depressions). The studied communities constitute the pioneer vegetation installed on free lands, bordering humid areas and which transitions is to other associations of shore weed formations, mesophilic or xero-mesophilic. They vary largely under the aspect of flora composition, physiognomy and ecology, are unstable and difficult to outline, because of the anthropic pressure they are exposed to and we consider them important because of their specific character.

pioneer vegetation, water shores, Romanian Banat

biology

Presentation: poster