In this study, the authors aimed to revise the ability of Solidago 9 niederederi, a hybrid between S. canadensis and S. virgaurea, to produce sexual ramets and seedlings as a part of its naturalization strategy. Based on a two-season garden cultivation experiment, we showed that the hybrid produces more generative ramets than vegetative ones and the number of generative ramets increases from one season to another with an increasing number of stem buds located on the caudices. We also revealed a spontaneous seedling recruitment by the hybrid during cultivation in the garden. Based on the seed germination test under laboratory conditions, we evidenced that the hybrid can reach a higher final germination percentage than S. canadensis but a lower one than S. virgaurea. Based on field studies conducted in 35 populations in Poland, the hybrid formed the largest populations in tree plantations and on abandoned fields, reaching 16.5 and 15.7 ramet clusters on average, respectively. The most abundant populations were found on abandoned fields; however, the mean number of ramets per cluster did not differ remarkably among habitats (H = 6.5, p = 0.163). In all populations, the mean number of vegetative ramets per cluster reached 0.85, while the generative ones achieved 6.43 on average. The statistical analysis proved that the aforementioned differences are significant (t = -12.6, p = 0.0002). Our results suggest that S. 9 niederederi is able to generate its own offspring by sexual reproduction and that abandoned fields seem to be the most suitable habitats for its establishment.

The investigations of habitat conditions on the variability of selected population features in the two invasive, annuals with different life-history traits were conducted in the years [2008][2009][2010], in the Polish part of the Carpathian Mountains in communities characterized by the gradual decrease of light availability. The individuals of Impatiens glandulifera were surveyed along roadsides, in willow thickets, as well as inside and along the edges of the riparian forest, whereas the individuals of Bidens frondosa were observed in riverside gravels characterized by a different species composition. Each year, the number and density of individuals (stems) occurring in the particular sites were examined, as well as the height and the fruit production in 30 randomly chosen stems were surveyed. Moreover, the number of seeds per fruit, the diaspore dimensions and the seedling recruitment in laboratory conditions were examined during each season. As the values of height of individuals, number of fruits per stem, number of seeds per fruit, as well as the seedling abundance in some groups were not consistent with the normal distribution and the variances were not homogeneous, the non-parametric Kruskal-Wallis test was used in statistical analyses. Much greater number and density of individuals of Impatiens glandulifera were found in riparian forest, than in willow thickets and along the roadsides. In all sites the number and density of individuals increased steadily in consecutive seasons. The great number and density of Bidens frondosa individuals observed in shady and partly shady sites during the first year of studies raised in the second year and subsequently dramatically decreased in the third season. The lowest number and density of individuals noted in the first season in unshaded site raised substantially in subsequent years. The height of stems, as well as seed and fruit production of both taxa diminished with a decrease of height of neighboring plants. The seed dimensions presented the spatial and temporal variability, whereas the number of seedlings among consecutive years and in successive sites did not differ. The considerable height of the individuals of Impatiens glandulifera, high production of large fruits and seeds in open and dry roadside areas can contribute to more effective ballistic dissemination, while substantial seedling recruitment enables the colonization of new, perhaps more advantageous sites. On the other hand, lower individual height, as well as fruit and seed production and considerable seedling emergence allow the population to last and to gradually extend the area in forest communities. The considerable abundance of the high-statured Bidens frondosa individuals, substantial production of large capitula and achenes contribute to long persistence of populations in open and sun-lit sites. The gradually decrease in the height of the stems, achene number and size observed in partly-shaded and shaded places might allow to long-distance dispersal of seeds by animals, while subst...

<p>In majority of plant communities with a closed canopy, the disturbances created by abiotic factors and biotic agents contribute to origin of an area free of existing vegetation and considered as safe sites for seedling recruitment. Although the gaps are characterized by several features, the size is proposed to be the most important characteristic. The investigations of recruitment of clonal taxa in different–sized gaps were conducted in the years 2011–2012 in <em>Molinietum caeruleae</em> meadows representing various successional stages and dominated by different species. Patch ES, representing early-successional stage, was dominated by small meadow species, Patch MS, representing mid-successional stage, was prevailed by tall-growing macroforbs, while Patch LS representing late-successional stage was overgrown by macroforbs and willows. In the successive sites the mean height of plant canopy, as well as the period of spring inundation increased gradually.</p><p>The total number of species and seedlings decreased from the Patch ES, through the Patch MS, to the Patch LS. Almost all plants presenting positive correlation between seedling number and gap area created hypogeogenous stems with substantial lateral growth and considerable number of short-lived daughter ramets allowing the fast colonization of neighbourhood. The majority of species showing negative relationship formed epigeogenous stems with slight lateral growth, as well as low number of long-lived ramets contributing to slow colonization of area.</p><p>In light of performed studies, it might be concluded, that making disturbance in continuous plant canopy and litter might be very effective way of conservation of <em>Molinietum caeruleae</em> meadows. The creation of different-sized gaps seems to be especially valuable due to the maintenance of heterogeneity of clonal species, which is particularly important in advanced successional stages.</p>

In this study, we investigated the influence of cold stratification on seed germination in S. × niederederi, a hybrid between the North American S. canadensis and the European S. virgaurea, using fruit samples collected in 2016 in Poland. We aimed to test the hypothesis that the low temperature exposure decreases the final percentage and speed of seed germination in the hybrid and its parental species. For each species, sets of 100 achenes in three replications were mixed with dry sand and stored in Petri dishes in darkness for 12 weeks, at −18 °C and + 4 °C, and + 25 °C. The seeds were incubated for 21 d at room temperature (+25 °C), under the 12 h photoperiod (630 lx). We showed a lack of significant differences in: (i) the final percentage of germinated seeds of studied species stored at the same conditions, (ii) the final percentage of germinated seeds between the applied stratification conditions in the hybrid and its parental species, and (iii) the mean values of Timson’s index, mean germination time, and coefficient of velocity of germination between the stratification conditions in each species. The statistically significant inter-specific differences in the mean germination time parameter after the +25 °C treatment suggest that the seeds of S. × niederederi are able to germinate faster than the seeds of its parental species. However, to improve our knowledge of naturalization and invasion abilities of S. × niederederi by sexual reproduction, the seed germination and seedling survival of the hybrid should be tested in the field.

Introduction Spontaneous hybridization between alien and native plant species has been well documented worldwide, reflecting the ongoing human influence on the geographical distribution of plants and biotic homogenization (Daehler and Carino, 2001; Bleeker et al., 2007; Stace et al., 2015; Klonner et al., 2017). Interestingly, hybridization between alien and native plant species is understood as a source of new alien taxa (Pyšek et al., 2004), and the ability to hybridize with native congeners appears to be a very useful criterion in the determination of the invasiveness of alien plants (Blackburn et al., 2014; Klonner et al., 2017). In extreme cases, hybrids between alien and native plant species cause the local extinction of native parental species by introgressive hybridization (Blackburn et al., 2014). It is commonly known that plant hybrids are morphologically intermediate between their putative parental species (Stace, 1989; Wilson, 1992; Stace et al., 2015). However, morphological intermediacy does not always provide hybrid origin and can be a result of divergence (Wilson, 1992). Numerous methods have been developed to prove hybridity based on intermediate morphology (e.g., hybrid index, principal component analysis, and pictorialized scatter diagrams); unfortunately, many of them are not useful in distinguishing hybridity from divergence (Wilson, 1992 and the literature cited therein). According to Wilson (1992), the best way to infer hybridity from morphological intermediacy is to specifically show character-by-character intermediacy, referred to as the character count procedure. This method has been successfully applied in many plant hybrid studies (e.g.,

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Abstract:The observations were carried out in the years [2007][2008][2009][2010], in the Molinietum caeruleae meadows with different habitat conditions located in Kraków-Kostrze (southern Poland). The greatest number of seedlings of Trollius europaeus and Iris sibirica was recorded in patches dominated by low-statured species with delicate, procumbent stems or small-tussocks. The diminishing of offspring emergence in places prevailed by large-tussocks grasses, as well as in sites overgrown by willows could be a consequence of poor harvesting practices, as well as the stagnation of water in local depressions. Irrespective of patch charracter, the seedling recruitment did not occur in a fully compact plant canopy, the highest number of offspring was observed in gaps without moss and necromass layers, while the greatest abundance of genets was found in openings left after the removal of bryophytes, litter and above ground parts of plants. The decrease in offspring number noted in gaps resulted from the removal of living and died plants combined with top soil raking, which might caused the partial depletion of soil seed bank reserves. Regardless of the patch type, a significantly higher appearance of seedlings of Trollius europaeus and Iris sibirica was found in the largest gaps than in the smallest ones. In light of the performed studies, it might be concluded that gap creating seems to be a very effective way of active protection of Iris sibirica and Trollius europaeus populations.

In climbing plants, fruits can be formed at different heights, depending on the height of external support. However, the effect of height on fruit and seed traits in invasive vines of Cucurbitaceae has not been intensively studied so far. In Europe, Echinocystis lobata, a North American member of Cucurbitaceae, is considered one of the most abundant invasive alien plants spreading in natural riparian forests, thickets, and tall herbs, whereas it is a rare species in urban woodlands. In this study, we tested the variability of selected fruit and seed traits of E. lobata in connection with habitat origin (natural, semi-natural, and anthropogenic), habitat type (using the EUNIS habitat classification), height (the distance between the fruit and the ground), and geographical position. The study was conducted in 2018 in 65 sites located in Latvia, Lithuania, Poland, and Slovakia. In each study site, a random sample of 10 fresh mature fruits of E. lobata was collected from subsequent 0.50 m intervals of height. The length, the width, and the weight of the fresh fruits, as well as the total number of seeds and number of undeveloped seeds per fruit, were examined. Moreover, the well-developed seeds from selected study sites were weighed. The statistical analysis showed the significant effect of habitat origin, habitat type, and height on most of the studied fruit and seed traits. The largest range of height (from 0.00 to 4.00 m) was observed in two types of habitats (F—heathland, scrub, and tundra; and G—woodland, forest, and other wooded land). The total number of seeds per fruit was positively correlated with the length, width, and weight of the fresh fruits. The fruits were a little heavier and bigger in natural habitats located in the northeast of the study area. The distribution of fruits at different heights may contribute to better dispersal of seeds by animals and wind, and may also better protect the seeds from being eaten by granivorous animals. The defence against seed-eating animals is expected to be stronger in semi-natural habitats, as well as on banks and shores of inland surface waters, where the seed production is the highest. The influence of seed traits on seed germination and seedling survival in various habitats and their importance in the invasiveness of E. lobata require further study.