The study was performed based on an inventory of alien flora in Daugavpils City. During the field studies all the alien species were recorded applying a regular grid consisting of 344 quadrats of 500 m × 500 m. Data of the 84 quadrats that cover all railway lines in the city were analysed to identify relationships between the distribution of alien plants and the location of railway lines. First the obtained data were compared with the first flora inventory in the city, which was conducted from 1975 to 1983. Comparison of data of the previous inventory and those obtained by us showed that the number of the recorded alien taxa along railways differed: 95 and 38 taxa, respectively. Secondly, some factors affecting the distribution of alien species along railway lines were analysed. Obtained results indicate that the highest concentrations of alien plants occurred in areas where railways are crossing or are located close to the adjacent cultivated and abandoned allotments, areas of private houses or cemeteries. Railway management measures such as topsoil disturbance and application of herbicides were found to be important human-induced factors affecting the distribution of annual alien taxa. The results of geospatial and statistical analyses demonstrated that the geographical distribution of alien species in general did not coincide with railway lines. However, the distribution of three species, i.e. Dracocephalum thymiflorum, Erysimum durum, and Lappula squarrosa, was associated only with railway lines, demonstrating the importance of railway infrastructure elements for the expansion of these species.

Categorisation of invasive alien species based on their impact is an important way to improve the management of biological invasions. The impact of 35 alien plant species in Latvia was evaluated based on information in the literature and certain studies of their environmental and socioeconomic impacts. As a result, 15 priority monitorable species, or the Black List, have been evaluated, for which seven of the nine criteria set were met. The other 20 invasive plant species make up the list of monitorable invasive plants, or the Grey List. The list and methodology developed during the study were approbated in the vegetation season of 2016 in 16 randomly selected monitoring quadrates, which were further stratified according to geobotanical regions of Latvia, which is proportionally 1,57% from all 1017 quadrates of Latvia. In total, 34 alien species were identified during approbation of methodology as showing signs of invasiveness: 10 from Black List, 10 from Gray List and 14 other invasive species, not included in the monitorable species list of developed monitoring methodology. In general, half of the species found during approbation of the methodology are trees and shrubs that were deliberately imported into Latvia in the past to be used in landscape gardening. A large proportion (41%) of the invasive species encountered come from North America. The most commonly encountered invasive species are Elodea canadensis Michx., Impatiens parviflora DC. and Solidago canadensis L. The data obtained through the field approbation show that the areas rich in invasive species are covered by forests and transit corridors, but the areas where no invasive species have been detected are transition mires and raised bogs as well as intensively managed farmland. Following the developed methodology, it was concluded that 50% of the quadrates to be monitored should be randomly selected while maintaining the principle of geobotanical regions, while the other 50% should be selected in previously known invasive plant populations.

Evarts-Bunders P., Evarte-Bundere G., 2018: New knowledge about species of the genus Chaerophyllum (Apiaceae) in Latvia. - Botanica, 24(2): 115-123. The genus Chaerophyllum belongs to the Apiaceae family, which is one of the most complicated and difficult to identify in Latvia. There are five species verified by herbarium materials known in Latvia: Chaerophyllum aromaticum - native species, rather frequent in all regions in forests, parks and shrublands, C. aureum - anthropophyte, known only from one locality in Daugavpils city along the railway, C. bulbosum - anthropophyte, earlier grown as a root vegetable and now found rarely in parks, at roadsides, waste places, along fences and under canopy of trees close to human settlements, C. hirsutum - native species, known from several localities only in south-eastern part of Latvia, mostly in the Daugava valley - forested ravines, slopes of broad-leaved forests, and C. temulum - alien species, known only from few localities - waste places, railway sides and old manor parks in the whole territory of Latvia. The most striking results are related to the distribution of C. hirsutum in Latvia. The literature sources and herbarium material of Anthriscus nitida, previously known and collected in Latvia, after our critical revision are considered as Chaerophyllum hirsutum, whereas Anthriscus nitida at least in the Latvian flora has not been identified yet and has been removed from the flora lists by mistake.

Evarte-Bundere G., Evarts-Bunders P., 2013: Use of leaf morphometric parameters for identification of the most common cultivated intraspecific taxa of Tilia platyphyllos [Morfometrinių požymių panaudojimas dažniausiems kultūriniams Tilia platyphyllos vidurūšiniams taksonams apibūdinti]. - Bot. Lith., 19(2): 83-90. To determine variation of the most important morphological parameters of Tilia platyphyllos Scop., we studied four most frequently found in Latvia taxa: T. platyphyllos subsp. platyphyllos, T. platyphyllos subsp. cordifolia (Besser) C.K.Schneid., T. platyphyllos ‘Rubra’, T. platyphyllos ‘Obliqua.’ Morphometric measurements (length of petioles, width and length of leaf blades, pubescence and margin of leaves) were performed for 10 different specimens of every selected taxon measuring five typical leaves from each specimen. The cultivated intraspecific taxa of Tilia platyphyllos differed by the following morphometric parameters - the pubescence of leaves, the margin of leaves and the length of leaf blades. No significant differences were ascertained between taxa in such morphometric parameters as the width of leaf blades and the length of petioles.

Rūrāne I., Evarts-Bunders P., Nitcis M., 2018: Distribution trends of some species of the Brassicaceae family in Latvia. - Botanica, 24(2): 124-131. The aim of this paper was to clarify and analyse the distribution trends of some Brassicaceae species (Bunias orientalis, Sisymbrium volgense, Barbarea arcuata, Draba nemorosa and Camelina alyssum) in Latvia. Field studies and the herbarium material analyses were carried out. The distribution trends were analysed by comparing all selected species in three time periods: by 1940, from 1941 to 1990, and from 1991 to the present. The study shows that the distribution of Brassicaceae species such as Bunias orientalis, Sisymbrium volgense, Barbarea arcuata and Draba nemorosa has increased significantly in Latvia during the time period from 1991 to the present, and these species are mostly found on railway, ruderal areas and roadsides, which are important habitats for species distribution. The occurrence of Camelina alyssum has considerably declined or perhaps the species has even disappeared from the flora of Latvia, which has been affected greatly by changes in the cultivation of agricultural crops as well as in agricultural land management.