Liparis loeselii is a declining orchid species in almost all European countries, mostly because of habitat loss. Therefore, good knowledge about the species ecology, distribution and populations is required in order to substantiate measures for its conservation. The aim of this research was to evaluate all available information about distribution, habitat types and population sizes of L. loeselii in Lithuania, in order to reveal the current state of our knowledge and identify information gaps. The study was based on the analysis of herbarium specimens and information in publications and various databases (a total of 481 unique records were used: 118 from herbaria, 121 from literature and 242 from databases). Intensive accumulation of information about L. loeselii started in the second half of the 20th century and a particularly large number of records were made in the period from 2010 to 2015 during the implementation of inventory and mapping of EU Habitats all over Lithuania. A summary of all information about L. loeselii revealed that it was registered in a total of 93 grid squares, and is mainly confined to uplands. The available information is quite sufficient for the evaluation of the species distribution and prevailing habitats, but is incomplete for the evaluation of population sizes, demographic structures and population trends under changing habitat conditions. Additional investigations are, therefore, required to enable a more accurate assessment of the size and viability of the L. loeselii metapopulation in Lithuania.
Woody plant species in recent decades have increasingly often been recorded escaped from cultivation and naturalized. In 2013, a new alien woody species Amorpha fruticosa L. (Fabaceae) was first found in Lithuania. In several Central European countries, A. fruticosa is recognized as invasive species that pose serious threat to natural habitats and ecosystems. To date, A. fruticosa has been registered in three localities in Lithuania: two populations in Ukmergė district and one population in Prienai district. Considering the present state of revealed A. fruticosa populations, it is concluded that this species in Lithuania is already naturalized and potentially invasive. Estimated total area occupied by A. fruticosa in three known localities is about 0.2 ha. In certain areas this species can become abundant and invade significant areas of meadow, forest-edge and other open habitats. Therefore, its immediate control and subsequent eradication can reduce risk of future invasion. Cultivation of A. fruticosa should be forbidden outside the ornamental plantations.
Two species of the genus Thesium (T. ebracteatum and T. linophyllon) are constantly recognized as members of the flora of Lithuania. However, the study on plants currently occurring in Lithuania and usually identified as T. linophyllon revealed that in fact they belong to T. ramosum. The analysis of all available data on the occurrence of T. linophyllon in Lithuania indicated that this species has never been recorded. The report on the occurrence of T. linophyllon, published at the end of the 18th century, was based on misidentified T. ebracteatum. Thus, T. linophyllon should be excluded from the list of vascular plants of Lithuania. Occurrence of T. ramosum was reported for the first time in the country. Currently, one population of this species with two subpopulations are known in the environs of Varnikai village (Trakai distr., Trakai Historical National Park). Morphological description of T. ramosum and diagnostic features of this species were provided. The structure and habitat conditions of two subpopulations were investigated in 2017. The present population of this species was revealed to consist of 52 individuals. Occurrence of young individuals in one subpopulation indicates generative reproduction of T. ramosum. Negative relationship between the number of T. ramosum individuals and the coverage of Poaceae species, and positive relationship between the coverage of Fabaceae species were revealed. Localities of T. ramosum in Lithuania are far from the area of its native distribution, and this species is ascribed to the group of established alien species. Further spread and invasion of the species is not expected.
Many woody plant species that originate from various regions of the world have been introduced in other regions or continents and are used in ornamental gardening, silviculture, erosion control, for fruit sources or other purposes. Woody plants selected for introduction usually originate from regions with similar climate conditions; therefore, after certain time lag they start to spread outside places of cultivation, become naturalized or even invasive. In addition to 77 woody alien plant species reported in Lithuania, ten new species were recorded and analysed in this paper. Information on the native and anthropogenic ranges, first record in Lithuania, size of populations, habitats, reproduction and naturalization of Aralia elata, Berberis thunbergii, Caragana frutex, Celastrus orbiculatus, Cornus alba, Cytisus austriacus, Hydrangea arborescens, Pinus strobus, Rhus typhina and Thuja occidentalis is presented. All these species have been introduced intentionally and are used mainly in ornamental gardening. Three of the reported species, Berberis thunbergii, Hydrangea arborescens and Thuja occidentalis, currently are casual species. Remaining seven species were recognized as naturalized in Lithuania, and five of these, i.e. Aralia elata, Celastrus orbiculatus, Cornus alba, Pinus strobus and Rhus typhina as well as Berberis thunbergii, which currently is treated as a casual, have very high or high probability of getting invasive. Constant survey of potential habitats, detection of new escaped alien plants, particularly of trees and shrubs, is the best way to reveal potentially dangerous species and make timely decisions for their control or eradication, if necessary.
The list of invasive alien species of European Union concern currently includes 23 plant species. The aim of this study was to assess the potential and importance of introduction pathways for invasive alien plant species in Lithuania, to estimate probability of their establishment and further spread in the country. Analysis of all available information revealed that three species (Asclepias syriaca, Heracleum sosnowskyi and Impatiens glandulifera) currently occur in Lithuania and the latter two are widespread invasive species in the country. The remaining 20 plant species have not been registered in the wild in Lithuania so far. Four of these, Gunnera tinctoria, Lysichiton americanus, Myriophyllum aquaticum and Pennisetum setaceum, are occasionally cultivated in gardens or other outdoor areas, and six species, e.g. Cabomba caroliniana, Eichhornia crassipes, Lagarosiphon major, are cultivated in aquaria or other indoor spaces. Naturalization of seven species is unlikely in the country, whereas naturalization of 13 species (Lysichiton americanus, Myriophyllum aquaticum, Pennisetum setaceum, etc.) is plausible. Five of the analysed and still not recorded species are recognized as potentially invasive in Lithuania; the invasion of five species is plausible and that of 10 species is unlikely. The most important pathway of introduction of the analysed species is ornamental gardening. Three species that have not been recorded in Lithuania, but occur in the neighbouring regions of Europe (Elodea nuttallii, Heracleum mantegazzianum, Heracleum persicum) can enter the country by natural means. Importance of permanent studies and surveys on alien plants aiming to ensure early detection and eradication of invasive species is discussed.