Acta Botanica 1-2017 - za web.indd ACTA BOT. CROAT. 76 (1), 2017 9 Acta Bot. Croat. 76 (1), 9–14, 2017 CODEN: ABCRA 25 DOI: 10.1515/botcro-2016-0040 ISSN 0365-0588 eISSN 1847-8476 Floristic composition of vegetation in habitats suitable for Erigeron × huelsenii (Asteraceae) Artur Pliszko*, Małgorzata Jaźwa Department of Taxonomy, Phytogeography and Paleobotany, Institute of Botany, Jagiellonian University, 31 Kopernika Street, 31-501 Kraków, Poland Abstract – The paper provides data on the fl oristic composition of vegetation in anthropogenic habitats suit- able for Erigeron × huelsenii, a spontaneous hybrid between the alien E. canadensis and native E. acris s. str. The study is based on 21 phytosociological relevés (vegetation plots) of 5×5 m size made in 2013–2014 in the Polish part of the Lithuanian Lakeland (north-eastern Poland) using the Braun-Blanquet method. The plots were taken on a roadside verge, a roadside slope, in abandoned sand and gravel pits, and on arable fi elds with grass-legume mixtures. There are 91 species of vascular plants, four species of bryophytes, three species of lichens, and one species of cyanobacteria. Vegetation is represented by populations of species typical of plant communities from the classes Stellarietea mediae, Artemisietea vulgaris, Koelerio-Corynephoretea, Festuco- Brometea and Molinio-Arrhenatheretea. Two fl oristic groups recognized from hierarchical cluster analysis and principal component analysis correspond with ruderal and segetal habitats. The study reveals that arable fi elds with grass-legume mixtures on sandy soils can be very suitable for E. × huelsenii. Keywords: anthropogenic habitat, Braun-Blanquet method, Erigeron acris, Erigeron canadensis, invasive species, multivariate analysis, plant hybridization * Corresponding author, e-mail: artur.pliszko@uj.edu.pl Introduction Habitats disturbed by human activities play a major role in the process of hybridization between alien and native plant species (Vilà et al. 2000, Daehler and Carino 2001, Blair and Hufbauer 2010, Guo 2014). It has long been rec- ognized that disturbance can bring two parental species into close proximity, increasing rates of cross-pollination and hybridization. Moreover, disturbance often creates interme- diate habitats that are especially suitable for hybrids (An- derson 1948, Daehler and Carino 2001). Hybridization in- volving alien and native species used to be viewed as one of the indirect effects of biological invasions (Vilà et al. 2000). Nowadays, it is an impact mechanism taken into consider- ation in the classifi cation of alien species (Blackburn et al. 2014). Spontaneously occurring hybrids between alien and native plants have been well-documented (Vilà et al. 2000, Daehler and Carino 2001, Bleeker et al. 2007, Lehman et al. 2014, Stace et al. 2015), and according to Pyšek et al. (2004) they must be understood as alien plant species. In Europe, Erigeron canadensis L. (≡ Conyza canaden- sis (L.) Cronquist) (Asteraceae), one of the commonest alien plants of North American origin (Weaver 2001, Lamb- don et al. 2008), hybridizes with a native congener E. acris L. s. str. giving a hybrid known as E. × huelsenii Vatke (≡ × Conyzigeron huelsenii (Vatke) Rauschert). The hybrid has been reported from the United Kingdom, Belgium, Germa- ny, the Czech Republic, Slovakia and Poland (Wurzell 1995, Šída 2000, Bleeker et al. 2007, Danihelka et al. 2012, Verloove and Lambinon 2014, Pliszko 2015, Stace et al. 2015). It is characteristically found as a single plant or in small numbers together with the parental species in dis- turbed areas, and is considered to be completely sterile (Stace et al. 2015). The alien parent E. canadensis is a spe- cies of ruderal and segetal communities of the class Stella- rietea mediae, and the native parent E. acris s. str. is a spe- cies of semi-natural dry grassland communities of the classes Koelerio-Corynephoretea and Festuco-Brometea and ruderal communities of the class Artemisietea vulgaris (Mucina 1997, Šída 2004, Pliszko 2015). Both parental species are light-demanding plants and occur on mineral, mesotrophic, usually dry soils (Zarzycki et al. 2002). Due to its ephemeral occurrence and intermediate morphologi- cal features the hybrid is easily overlooked during fl oristic and ecological fi eld surveys. In consequence, phytosocio- logical studies on habitats suitable for E. ×huelsenii have not been undertaken. In this paper we aimed to compare the fl oristic composition of vegetation in disturbed places in PLISZKO A., JAŹWA M. 10 ACTA BOT. CROAT. 76 (1), 2017 Poland where the spontaneous hybridization between E. ca- nadensis and E. acris s. str. occurs. Materials and methods Study area The study was conducted in seven newly discovered lo- calities of Erigeron × huelsenii in the Polish part of the Lithuanian Lakeland, north-eastern Poland (On-line Suppl. Fig. 1, Tab. 1). This lowland area is located in a transitory temperate climate zone with some infl uence from the conti- nental climate. In the period 1971–2000 the average annual air temperature was about 6.5 °C, and the average annual precipitation was 550–600 mm (Lorenc 2005). The native vegetation is represented mainly by nemoral forest commu- nities with boreal and subboreal infl uences (Szafer and Zar- zycki 1972), however, the area is highly deforested and has an agricultural character. The soils in the studied sites de- veloped from the glacial-fl uvial sands and gravels deposit- ed during the Vistula Glaciation (Ber 1981). Sampling A total of 21 phytosociological relevés (vegetation plots) of 5×5 m size were made in 2013–2014 in open an- thropogenic habitats, including one plot on a sandy road- side verge, one plot on a sandy roadside slope, eight plots in abandoned sand and gravel pits, and 11 plots on sandy ara- ble fi elds with grass-legume mixtures (Tab. 1). Visual esti- mation of cover-abundance in plots was based on the wide- ly applied Braun-Blanquet method (Braun-Blanquet 1964, Westhoff and van der Maarel 1973). Names of taxa fol- lowed Mirek et al. (2002), Wójciak (2003), and Siemińska and Wołowski (2003). Taxonomic treatment of Erigeron followed the concept proposed by Greuter (2003). Names of syntaxa and diagnostic species followed Mucina (1997). Taxa were identifi ed using morphological features given by Wójciak (2003), Rutkowski (2004), Keshari et al. (2015), and Stace et al. (2015). Geographical-historical status of vascular plants is according to Mirek et al. (2002) and To- karska-Guzik et al. (2012). Hybrids between alien and na- tive plant species are treated as alien species (Pyšek et al. 2004). Voucher specimens of E. × huelsenii collected dur- ing the fi eld studies are deposited in the Herbarium of the Institute of Botany of the Jagiellonian University in Kraków (KRA). Data analysis Cover-abundance values of the Braun-Blanquet scale were transformed to the numerical 1–9 scale (van der Maarel 1979). The vegetation plots were analyzed by multi- variate methods. Data analyses were performed using MVSP version 3.1 (Multivariate Statistical Package) (Ko- vach 1999). The Jaccard similarity index was used to esti- mate the species composition similarity between the vege- tation plots. The dendrogram was prepared using the unweighted pair group method with arithmetic mean (UP- GMA). The scatter diagram was prepared using the proce- dure of principal component analysis (PCA). Results All vegetation plots together contain 91 species of vas- cular plants (excluding microspecies of the genus Taraxa- cum), four species of bryophytes, three species of lichens, and one species of cyanobacteria. There are 15 alien species and three species of uncertain geographical-historical status in the Polish fl ora. The plots sampled on arable fi elds in- clude fi ve species cultivated as fodder crops (grass-legume mixtures), namely Dactylis glomerata L., Lolium perenne L., Medicago sativa L., Phleum pratense L. and Trifolium pratense L. (On-line Suppl. Tab. 1). The number of species per plot is 24.62 ± 6.20. The cover of individual species in plots is low, including Erigeron ×huelsenii and its parental species, and only in three cases it reaches 75% (i.e. Cala- magrostis epigejos (L.) Roth, Dactylis glomerata and Cera- todon purpureus (Hedw.) Brid.). Vegetation is represented by populations of species typical of plant communities from the classes Stellarietea mediae, Artemisietea vulgaris, Koelerio-Corynephoretea, Festuco-Brometea and Molinio- Arrhenatheretea (On-line Suppl. Tab. 1). Fig. 1. Dendrogram made on the basis of cluster analysis (unweighted pair group method with arithmetic mean and the Jaccard index) showing fl oristic similarity between the vegetation plots. Numbers (1–21) indicate respective relevés described in Tab. 1 and On-line Supplement Tab. 1. VEGETATION IN HABITATS SUITABLE FOR ERIGERON × HUELSENII ACTA BOT. CROAT. 76 (1), 2017 11 From the hierarchical cluster analysis (UPGMA) and principal component analysis (PCA) two main fl oristic groups were clearly recognized (Figs. 1–2). These groups correspond with ruderal and segetal habitats. The plots tak- en on a roadside verge (5), a roadside slope (2), and in abandoned sand and gravel pits (1, 6–9, 13–15) represent a group of ruderal habitats, whereas the plots taken on arable fi elds with grass-legume mixtures (3, 4, 10–12, 16–21) rep- resent a group of segetal habitats. The herb layer has a low- er cover in plots sampled in ruderal habitats than those sam- pled in segetal habitats, but the moss layer has a higher cover in ruderal than in segetal habitats. Moreover, in seven plots taken on arable fi elds there is no moss layer (On-line Suppl. Tab. 1). Discussion Based on this study spontaneous hybridization between Erigeron canadensis and E. acris s. str. occurs in two fl oris- tically different types of anthropogenic habitats in Poland. Tab. 1. Location, date of sampling and habitat description of plots sampled for the study. According to the ATPOL cartogram method (Zając 1978) the capital letters indicate 100-km square, whereas the numbers indicate 10-km square; m.a.s.l. – meters above sea level. Plot no. Locality GPS coordinates Altitude (m.a.s.l.) ATPOL cartogram unit Habitat Date 1 Suwałki near Sobolewo 54°4′ 43.8″ N 22°57′ 30.18″ E 159 FB18 abandoned sand and gravel pit 7 August 2013 2 Filipów Czwarty 54°9′ 54.24″ N 22°36′ 57.54″ E 195 FB06 sandy roadside slope 9 August 2013 3 Filipów Pierwszy 54°9′ 49.32″ N 22°37′ 6.84″ E 185 FB06 sandy arable fi eld with grass-legume mixture 16 August 2013 4 Filipów Pierwszy 54°9′ 49.44″ N 22°37′ 5.4″ E 186 FB06 sandy arable fi eld with grass-legume mixture 16 August 2013 5 Kamionka Stara near Bakałarzewo 54°4′ 46.2″ N 22°40′ 48.18″ E 164 FB17 sandy roadside verge 18 August 2013 6 Suwałki near Sobolewo 54°4′ 43.8″ N 22°57′ 25.8″ E 158 FB18 abandoned sand and gravel pit 6 August 2014 7 Suwałki near Sobolewo 54°4′ 44.64″ N 22°57′ 28.56″ E 157 FB18 abandoned sand and gravel pit 6 August 2014 8 Suwałki near Sobolewo 54°4′ 11.64″ N 22°58′ 5.88″ E 159 FB18 abandoned sand and gravel pit 6 August 2014 9 Suwałki (former Żwirownia PKP) 54°6′ 26.58″ N 22°53′ 55.8″ E 173 FB08 abandoned sand and gravel pit 8 August 2014 10 Mieruniszki 54°8′ 57.96″ N 22°34′ 19.5″ E 196 FB06 sandy arable fi eld with grass-legume mixture 10 August 2014 11 Mieruniszki 54°8′ 58.26″ N 22°34′ 21.36″ E 195 FB06 sandy arable fi eld with grass-legume mixture 10 August 2014 12 Mieruniszki 54°9′ 2.34″ N 22°34′ 21.24″ E 196 FB06 sandy arable fi eld with grass-legume mixture 10 August 2014 13 Suwałki near Sobolewo 54°4′ 14.64″ N 22°57′ 57.12″ E 162 FB18 abandoned sand and gravel pit 18 August 2014 14 Suwałki near Sobolewo 54°4′ 14.58″ N 22°58′ 0.6″ E 157 FB18 abandoned sand and gravel pit 18 August 2014 15 Suwałki near Sobolewo 54°4′ 14.46″ N 22°58′ 2.04″ E 158 FB18 abandoned sand and gravel pit 18 August 2014 16 Ostrowo near Pluszkiejmy 54°16′ 55.26″ N 22°27′ 11.58″ E 180 FA85 sandy arable fi eld with grass-legume mixture 7 September 2014 17 Ostrowo near Pluszkiejmy 54°16′ 56.34″ N 22°27′ 12.24″ E 180 FA85 sandy arable fi eld with grass-legume mixture 7 September 2014 18 Filipów Czwarty 54°10′ 5.52″ N 22°36′ 52.02″ E 195 FB06 sandy arable fi eld with grass-legume mixture 8 October 2014 19 Filipów Czwarty 54°10′ 5.82″ N 22°36′ 52.2″ E 195 FB06 sandy arable fi eld with grass-legume mixture 8 October 2014 20 Filipów Pierwszy 54°9′ 50.16″ N 22°37′ 6.18″ E 187 FB06 sandy arable fi eld with grass-legume mixture 9 October 2014 21 Filipów Pierwszy 54°9′ 49.32″ N 22°37′ 4.68″ E 186 FB06 sandy arable fi eld with grass-legume mixture 9 October 2014 PLISZKO A., JAŹWA M. 12 ACTA BOT. CROAT. 76 (1), 2017 These types concern ruderal and segetal areas. It has been reported that E. × huelsenii occurs mainly in places of a ru- deral character such as sand pits, roadside verges, disused ironworks, railway areas (Wurzell 1995, Crompton and Preston 2001, Verloove and Lambinon 2014, Stace et al. 2015), but its occurrence in segetal habitats is poorly recog- nized. What is interesting is that the vegetation in all plots sampled in ruderal habitats represents an early stage of sec- ondary succession where there are no tree and shrub layers, and the cover values of the herb and moss layers are gener- ally low. Moreover, the early stage of secondary succession in these habitats can be characterized by the presence of epigeic species of cyanobacteria, lichens and bryophytes, as was pointed out by Langhans et al. (2009). In segetal habi- tats sampled for the study, in contrast, the process of sec- ondary succession is hindered by the regular cutting of grass-legume crops for hay, thus there are no woody plant species. Nevertheless, many herbaceous plants can thrive in arable fi elds with grass-legume mixtures as weeds (Sander- son et al. 2013), especially on poor sandy soils where the canopy of cultivated plants is usually not dense or there are gaps in the canopy. The results of principal component analysis (Fig. 2) show that the group of ruderal habitats is fl oristically more heterogeneous than the group of segetal habitats. This can be explained by the fact that in the early stages of secondary succession, abandoned sand and gravel pits are readily colonized by various plant species typical of ruderal, grassland and meadow communities (Řehounková and Prach 2006). In the vegetation plots sampled for the study most of the associated species with the highest con- stancy are light-demanding plants and occur usually on dry, mesotrophic or oligotrophic, sandy soils (e.g. Artemisia campestris L., Hieracium pilosella L. and Sedum acre L.), like E. canadensis and E. acris (Zarzycki et al. 2002). Wur- zell (1995) suggested that persistence of E. × huelsenii in ruderal habitats depends on competition from more vigor- ous wayside and wasteland perennial plants. Moreover, it appears that the changes in the light conditions caused by the overgrowth of trees and shrubs can limit the occurrence of the hybrid and its light-demanding parents, especially in abandoned sand and gravel pits where some woody plants are already present in the herb layer (i.e. Betula pendula Roth, Malus domestica Borkh., Pinus sylvestris L. and Pop- ulus tremula L.). For all of the aforementioned reasons, we assume that E. × huelsenii occurs in ruderal and segetal habitats due to favourable light conditions and to the pres- ence of canopy gaps in which the hybrid seedlings can sur- vive the competition from other plants. In this paper the fl oristic composition illustrates the summer and autumn aspects of vegetation. The late time of plot sampling is a consequence of the phenology of E. × huelsenii. It is hard to fi nd and identify vegetative individu- als of the hybrid in spring. Besides, in the case of arable fi elds with grass-legume mixtures, when there is the second cutting of crops, the hybrid is visible only after regrowth. It is also worth mentioning that in plot number 17 (located in an arable fi eld with grass-legume mixture) two spontaneous hybrids between alien and native plants were recorded, namely E. × huelsenii and Solidago × niederederi Khek, which seems to be a very unusual situation (On-line Suppl. Tab. 1). In Poland, E. canadensis is treated as a nationally inva- sive alien species (Tokarska-Guzik et al. 2012). It is able to appear in large numbers, mainly in anthropogenic habitats, and hybridization with a native relative E. acris s. str. is one of its neglected impacts. Although E. canadensis and E. ac- ris s. str. are commonly distributed in the country (Zając and Zając 2001), and often share habitats, the hybrid E. × huelsenii is rarely found (Pliszko 2015). Its rarity is a re- fl ection of the fact that it is usually overlooked by taxono- mists and ecologists during fi eld surveys. Fig. 2 Scatter diagram presenting the results of principal component analysis (PCA) for the studied plots. Numbers (1–21) indicate re- spective relevés described in Tab. 1 and On-line Supplement Tab. 1. Selected species are represented by arrows. VEGETATION IN HABITATS SUITABLE FOR ERIGERON × HUELSENII ACTA BOT. 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