New station of Orobanche coerulescens from xerothermic grassland in Bohukały near Terespol, Lublin Province (Podlaski Przełom Bugu) is given in the paper. It is the only one, confirmed station of this species in Poland.

Studies carried out between 1995 and 2001 on Iris sibirica allowed to discover 7 new stations and established condition of populations of the species in the Południowopodlaska Lowland. Among from 30 stations of Iris sibirica noted in the studied area, presence of 16 was confirmed. Decline in abundance of species are related to diminish of acreage of wet meadows [Molinietalia] due to both agriculture intensification and secondary succession of abandoned meadows. Avoiding anthropopressure [12 from 16 examined stations] populations of Iris sibirica pass to forest, shrub, and forest edge communities. Detailed descriptions of stations with phytosociological records, state of endangered and main threat agents for each population are also given.

Studies were carried out of three populations of Listera ovata from Siedlce environs (Siedlecka Upland). Two of them were situated at anthropogenic (Mościbrody and Rybakówka) and one at natural (Kisielany) stations. Biometric measurements of individual and group features were realized between 1996 and 1999. Aboundance of the studied populations of Listera ovata is much higher in comparison with aboundance of other populations in the scale of the country. Most aboundant populations were observed on antropogenic stations. However human activity also does not significantly affect the features of particular specimens.

Thermomyces lanuginosus is the most popular thermophilic fungi. The morphological characteristic and the determination of the cardinal temperatures of the isolated tribes was the aim of this study. The material of the study were 22 samples. The presence of Thermomyces lanuginosus was found in 6 samples, in which isolated 148 species. The study has proved, that species of this fungus produce the mycelium in different colours. Optimum temperatures for growth was 45-55°C, minimum 30°C and maximum 60°C. The growth and development at 25° and 65°C wasn’t observed.

The thermophilic fungus Thermomyces lanuginosus (syn. Humicola lanuginosa) used was isolated from the hazelnuts. Their lipolytic activity was determinated by incubating liquid cultures at 55°C with relation to sunflower oil, soybean oil, rapeseed oil and olive oil. The highest lipolytic activity was observed with relation to sunflower oil and the least one – in the presence of olive oil.

Characteristic of segetal communities of order Centauretalia cyani, occurring in the administrative borders of Siedlce is presented in the paper. Presence of 2 associations and 4 communities, differentiated internally into: 2 subassociations, 8 variants and 3 subvariants. Totally 15 phytocoenoses of the lowest units were distinguished. The largest areas of the city cultivations were occupied by communities without characteristic species for described segetal associations, as: incomplete community of all. Aperion spicae-venti. Plots of association Vicietum tetraspermae were also frequent in the studied area. Presence of floristically rich plots of Papaveretum argemones – association of cereal weeds rarer and rarer noted in Poland is especially noteworthy. Segetal vegetation of Siedlce city is characterized by its floristic abundance and large participation of ruderal species passing from adjacent areas to arable lands.