The first European record of Lespedeza cuneata (Fabaceae), an invasive alien species of Union concern

In 2019, Lespedeza cuneata (Chinese bushclover), a subshrub native from Afghanistan to Japan, tropical Asia and eastern and southeastern Australia, was included in the second update of the EU Regulation 1143/2014. As a consequence, it is subject to restrictions on keeping, importing, selling, breeding and growing, although it should be noted that it had not been recorded in the wild so far in the European Union. In 2022, this species was recorded on the banks of the Vesdre river in Goffontaine in the easternmost part of Belgium. Details about this first European record are presented. In compliance with the Regulation, the single individual found was removed.


Introduction
The introduction of alien plants and their further expansion is an increasing phenomenon linked to economic activities that have caused significant damage to biodiversity in many areas (Dogra et al. 2010;Lososová et al. 2012).To combat the spread of such species, many countries and regions have adopted lists and measures to restrict species exchange.Several thousand non-native species have been introduced into the European Union (Keller et al. 2011), of which around 300 species of terrestrial plants have become invasive (Vilà et al. 2010).The problem of invasive alien species is specifically treated through the EU Regulation 1143/2014 of the European Parliament and of the Council of 22 October 2014 on the prevention and management of the introduction and spread of invasive alien species (https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:32014R1143) and by its subsequent modifications.
Lespedeza cuneata (Dum.Cours.)G. Don (Chinese bushclover) is a subshrub from the Fabaceae family.It is native from Afghanistan to Japan, tropical Asia and eastern and southeastern Australia.Elsewhere it is present as an introduced and often invasive species, for instance in the United States, where it was used for erosion control and reclamation of mine soils, hay, wildlife cover and food, for seed production and as a pasture species (Brundu et al. 2019).It is particularly harmful in tallgrass prairies (Varriano et al. 2020).Just because of its dubious reputation, it actually features on the European list of invasive alien species: in 2019, it was added to the second update of the EU Regulation 1143/2014, following a pest risk assessment from 2018 (Flory 2018;EPPO 2018;Brundu et al. 2019).The damage that it can cause is so significant that it justifies the adoption of dedicated measures applicable across the European Union.This was a precautionary measure as the species had never been found in the wild in the European Union.
In the summer of 2021, among more than 150 other exotic species (Verloove et al. in prep.), a single individual of Lespedeza cuneata was observed on the exposed bank of the Vesdre river in Belgium.It is the first documented record in the wild in the European Union.

Study area
The Vesdre river is about 70 km long and forms the northern border of the Ardennes.It belongs to the basin of the Meuse river and runs almost entirely through the province of Liège (Belgium).Its main tributaries are the Ghete, the Helle, the Gileppe and the Hoëgne.The river crosses cities such as Eupen, Limbourg, Verviers, Pepinster, Trooz and Chaudfontaine; it finally flows into the Ourthe in Chênée near Liège, which flows into the Meuse/Maas about three kilometers further on (Figure 1).Although in 2022 alien weeds were recorded more or less throughout the valley, a relatively small area in Goffontaine (Pepinster) was by far the most species-rich (Verloove et al. in prep.).It consists of a recently developed nature reserve, after excavating soil, on the left bank of the river, right in front of the water treatment plant (GPS coordinates: 50.5649, 5.7613; altitude 115 m.a.s.l.) (Figures 2, 3).
In the summer of 2021, the valley of the Vesdre faced unprecedented floods.As a result, the entire valley was destroyed and the banks of the river-for decades overgrown with the invasive weed Reynoutria japonica Houtt.-wereexposed again.Consequently, in the summer of 2022, seeds from the long buried sediment, which were introduced at least 50, but perhaps rather more than 100 years ago, most likely through the former wool processing industry, germinated.

Methods
With the aim of mapping the exotic flora that had germinated after the floods, the banks of the river were repeatedly surveyed between the 4 th of July and the 1 th of December 2022.Herbarium specimens were collected for all of the interesting records and these are preserved in the herbarium of the Meise Botanic Garden, Belgium (herbarium acronym: BR; Thiers 2023).All records were also registered on the observations.beonline platform (https:// observations.be/),data which were subsequently also uploaded in GBIF (Global Biodiversity Information Facility; https://www.gbif.org/).
The species was identified based on morphological characters according to Ohashi et al. (2009), Huang et al. (2010) and Adema (2019).

Results and discussion
On the 6 th of August 2022, a single non-flowering individual of a shrublike legume was observed in the study plot.Because, especially at the site in Goffontaine, damage was regularly caused by wild boars (Sus scrofa L.) and Canada Goose (Branta canadensis L.), it was dug out for cultivation ex situ soon afterwards.This individual started flowering a few weeks later.In the course of October, after having produced both (cleistogamous) flowers and fruits, this plant was identified as Lespedeza cuneata.Although according to some phylogenetic studies L. juncea (L.f.) Pers.and L. cuneata are distinct entities (e.g.Han et al. 2010;Xu et al. 2012), the morphological differences between these two species seem too small to separate them at any level.Adema (2019) therefore included L. cuneata in a broadly circumscribed L. juncea.Alternatively, L. cuneata is sometimes reduced to a subspecies or variety of L. juncea, respectively subsp.sericea (Miq.)Steenis or var.sericea (Miq.)F.B. Forbes & Hemsl.In the putative areas of origin of our plant material (Australia, South Africa and South America) only L. cuneata is known to occur and some morphological features (e.g.length of fruiting peduncle, length/wide ratio of leaflets; as far as reliable for their separation) also suggest this is the name to apply to our collection.Within the genus Lespedeza, the very short, almost sessile inflorescences are remarkable for this species (Adema 2019).It is further characterized as follows (Figures 4, 5).
In the nineteenth and until the mid-twentieth century, the Vesdre valley housed an important industry, processing wool imported from (mainly) Australia, South Africa and South America.The raw wool contained numerous seeds and fruits, often armed with spines or hooks (Visé 1942).Together with the waste water, these ended up in the river after which they could germinate downstream in favorable years.These past industrial activities no doubt explain the appearance of numerous exotic pasture weeds on the exposed river banks in 2022, many of them not recorded before outside their native distribution range (Verloove et al. in prep.).
In a Pest Risk Assessment for the European Union (EPPO 2018), under current climatic conditions, Belgium was not considered to be part of the "endangered area" since cool summer temperatures strongly limit the suitability of establishment in most of northern Europe.However, under climate change projections for Europe in 2070, the model predicts a pronounced northwards expansion of the suitable region; under this scenario Belgium would also become part of the endangered area.From our field observations in Belgium in 2022, it is clear that, under favorable climatic conditions, the species can reproduce from seed without difficulty.It is still unclear whether the species also would survive local winter conditions, although in North America it grows as far north as Nebraska (Brundu et al. 2019) where temperatures drop well below 0 °C during winter.
According to EPPO (2018) the most likely pathway for the introduction of Lespedeza cuneata in the European Union is through the horticultural trade.The species is offered for sale as an ornamental shrub (Cullen 2011), although probably on a small scale.Less likely pathways for its introduction are agriculture (the species was formerly grown for forage, especially in the Americas) and as a contaminant in hay and straw imports.This is in fact no wonder since the species is a major weed problem in pastures.
Lespedeza cuneata seeds are very hard coated.Available information suggests that this species forms persistent seed banks and that it is common to find seeds in soil samples where, however, no young or adult plants are found (Carter and Ungar 2002;Honu et al. 2009).In seed banks, its seeds are believed to remain viable for decades (Invasive.org2023) although, to our knowledge, no detailed studies on seed bank longevity and germination have been conducted under field conditions so far.Walters et al. (2005) studied the germination of (indoor) stored seeds of L. cuneata and found a germination rate of 7% after 27 years for seeds stored at 5 °C and 61% after 40 years for seeds stored at −18 °C.In previous trials, conducted by Pieters (1939), only a small percentage of the seeds germinated without prior treatment; however, scarification (chemical or physical) notably increased their germination rate.The species produces two types of seeds that seem to have a very different germination behaviour, a trait that has been commonly explained as an adaptive strategy of plant species that improves survival possibilities under unpredictable environments (Grime 1979).The particular circumstances in which the species was found in the study area, i.e. on a riverbank after massive floods, apparently have enhanced germination conditions: the floods and friction caused by currents may have helped to permeabilize the seed coat.In addition, germination of L. cuneata seems to be favored by soft burns, soil warming and biomass reduction (Blocksome 2006).The combination of extreme floods (and the associated removal of the alien invasive Reynoutria japonica) and the exceptionally warm summer and autumn of 2022 (the warmest ever registered in the area according to Copernicus data), probably have favored the germination and further development of L. cuneata.
The introduction vector of Lespedeza cuneata in the Vesdre valley cannot be unequivocally established.The species is not cultivated in this area, nor in surrounding areas.However, the former presence, further upstream in this valley, of industrial facilities dedicated to wool textiles may have played an important role in the past.In this particular area an intensive activity of washing and processing wool took place, particularly from the 19 th to the first half of the 20 th century.Wool was mainly imported from Australia, South Africa and South America (Visé 1942), areas where the species indeed is present.Yet, L. cuneata should have been a rather exceptional impurity since it had not been associated before with wool importation in Europe (e.g. Probst 1949;Clement and Foster 1994).Although the species can be dispersed by endozoochory, at first glance, the fruits or seeds are not particularly suited to be carried in sheep's wool (absence of hooks, prickles, needles, etc.); however, in a recent experimental study, its seeds were shown to be readily dispersed by mammals and the number of seeds retained was higher for animals with longer fur (Quick et al. 2016), such as sheep.In its area of origin, L. cuneata often is a predominant weed in sheep pastures (Gupta et al. 2007).Besides, the species was found along with dozens of other exotic species with obvious anatomical adaptations for animal dispersal.All this considered, the available information seems to point to wool (or hides, fur, etc.) as the most likely vector of introduction for L. cuneata.
As wastewater is no longer discharged into the river, the likelihood of seeds of newly imported alien species (including Lespedeza cuneata) germinating on the banks is non-existent; it can, of course, germinate from exposed anthropogenic seed banks as was the case in Belgium in 2022.This can as well happen in other EU countries that are actually located in the "endangered area" sensu Brundu et al. (2019); this particularly holds true for France and Germany, two countries where wool alien plants were recorded in the past (Probst 1949).In France, for example, the Tarn valley used to be known for its hides and furs processing industry and associated flora (e.g.Bernard and Fabre 1973;Auquier and Hansen 1976); local general conditions are very similar to those in the Vesdre valley.Even though exotic seeds are likely no longer to be encountered in wastewater, it should be borne in mind that wool waste is an excellent fertilizer: in the past it was widely used in orchards, fields and even private gardens in any area where wool was processed, also in the Vesdre valley in Belgium (Visé 1942).The so-called wool shoddy was a waste product of the woollen industry, i.e. fibres that were too short, of poor quality or too dirty to be useful, but evidently contained lots of foreign seeds (Shimwell 2006).The cessation of spreading wool shoddy may have largely curtailed the introduction of wool aliens.However, the use of wool waste as a soil amendment is again being researched today (e.g.Zheljazkov et al. 2009;Górecki and Górecki 2010;Bradshaw andHagen 2022, Broda et al. 2023).If this practice were to become more widespread again and the wool waste still contains fruits or seeds, then it is not impossible and even likely that wool adventives will re-occur in the future, wherever applied.
Early detection and Rapid eradication at an early stage of invasion are key when dealing with potentially invasive alien species (articles 16 and 17 respectively of the EU Regulation 1143/2014).In compliance with the Regulation, the species was therefore removed from its first European growing site.

Conclusion
The find of Lespedeza cuneata in the Vesdre river valley (Belgium) suggests that the species can emerge without human intervention long after the introduction route/associated industrial activity have disappeared.Hence, given its previous invasive history in the USA and elsewhere, it seems advisable to monitor its further presence in the area and step up monitoring efforts in order to cover a larger part of the basin, which would allow the early detection of self-sustaining populations.