British Flora Research Articles

The emerging importance of cross-ploidy hybridisation and introgression.

Natural hybridisation is now recognised as pervasive in its occurrence across the Tree of Life. Resurgent interest in natural hybridisation fuelled by developments in genomics has led to an improved understanding of the genetic factors that promote or prevent species cross-mating. Despite this body of work overturning many widely held assumptions about the genetic barriers to hybridisation, it is still widely thought that ploidy differences between species will be an absolute barrier to hybridisation and introgression. Here, we revisit this assumption, reviewing findings from surveys of polyploidy and hybridisation in the wild. In a case study in the British flora, 203 hybrids representing 35% of hybrids with suitable data have formed via cross-ploidy matings, while a wider literature search revealed 59 studies (56 in plants and 3 in animals) in which cross-ploidy hybridisation has been confirmed with genetic data. These results show cross-ploidy hybridisation is readily overlooked, and potentially common in some groups. General findings from these studies include strong directionality of hybridisation, with introgression usually towards the higher ploidy parent, and cross-ploidy hybridisation being more likely to involve allopolyploids than autopolyploids. Evidence for adaptive introgression across a ploidy barrier and cases of cross-ploidy hybrid speciation shows the potential for important evolutionary outcomes.

Genetic factors predict hybrid formation in the British flora

Natural hybridization can have a profound evolutionary impact, with consequences ranging from the extinction of rare taxa to the origin of new species. Natural hybridization is particularly common in plants; however, our understanding of the general factors that promote or prevent hybridization is hampered by the highly variable outcomes in different lineages. Here, we quantify the influence of different predictors on hybrid formation across species from an entire flora. We combine estimates of hybridization with ecological attributes and a new species-level phylogeny for over 1,100 UK flowering plant species. Our results show that genetic factors, particularly parental genetic distance, as well as phylogenetic position and ploidy, are key determinants of hybrid formation, whereas many other factors such as range overlap and genus size explain much less variation in hybrid formation. Overall, intrinsic genetic factors shape the evolutionary and ecological consequences of natural hybridization across species in a flora.

A molecular and morphological study of Leucobryum in Britain and Europe: the presence of L. albidum (P.Beauv.) Lindb. confirmed

ABSTRACT Introduction. Initial morphometric investigations into the differences between Leucobryum glaucum (Hedw.) Ångstr. and L. juniperoideum (Brid.) Müll.Hal. in Britain showed that some populations could not be clearly assigned to either species. An intensive morphological and molecular study was therefore undertaken to understand the diagnostic characters of the European species of the genus, including L. albidum (Brid. ex P.Beauv.) Lindb., whose reported presence in Europe was surrounded by uncertainty. There has been little agreement among previous authors on the relative taxonomic importance of the different morphological characters, or on their metrics. Methods. Molecular sequencing using nuclear and chloroplast markers, in conjunction with previously accessioned data, allowed judgement of the taxonomic importance of various methods for morphological discrimination. These methods included both existing published techniques and newly discovered diagnostic characters. This integrated process was cyclical, the morphological analysis being directed and confirmed by the sequencing of selected specimens. Results and discussion. Data are presented demonstrating the correlation between molecular identification and certain morphological characters in the three European species of Leucobryum. Leucobryum albidum is confirmed as a locally frequent member of the British flora and it is also shown to be present in Ireland and western part of continental Europe. Leucocyst pore morphology is described and its value as a diagnostic character is discussed. An identification key is provided for the three species. Plants from two sites are shown to have a discordance between nuclear and plastid molecular markers and we consider the possibility that horizontal gene transfer could explain the observed patterns.

Change in species distributions at tetrad scale – a supplement to Change in the British Flora 1987-2004

The report on BSBI’s ‘Local Change’ repeat tetrad survey (LC) was published in 2006 as Change in the British Flora 1987-2004. Excellent species distribution maps at tetrad (2 km) scale are now readily accessible on BSBI’s online Distribution Database (DDb). The opportunity has been taken to download a selection of such maps and match them with the species chosen for detailed accounts, including maps and statistics, in the LC Report. Statistics on species distribution change at tetrad scale have also been derived from data extracted from the DDb for England and Scotland comparing the dateclass 1987-99 with 2000-19. Further statistics have been derived for Bedfordshire v.c.30), where two complete surveys at tetrad scale have been completed. The statistics of change for the chosen species are expressed as ‘% Change per decade’. Taken together, the maps and statistics provide greater insight into the geographic patterns of change than was available at the time of the LC Report.

Snake’s-head Fritillary Fritillaria meleagris (Liliaceae) in Britain: its distribution, habitats and status

Snake’s-head Fritillary Fritillaria meleagris L. is a scarce plant of unimproved meadows where it was formerly considered to be a native British species. A review of 593 British sites showed that 80% of British populations were located in other habitats where it had been planted or had established from introductions nearby. Of the 118 populations located in unimproved meadows 53 occurred in floodplain grassland in central and southeast England where it has long been considered to be native. However, recent evidence suggests that it is more likely to be a modern introduction (neophyte). It seems inconceivable that such an attractive plant would have been overlooked in the wild by herbalists in the fifteenth and sixteenth centuries. Furthermore, the rapid growth of introduced populations in meadows in Sweden and England has shown that Fritillary populations in Britain could have reached their present size in the 300 years since they were first recorded in the wild. Historical accounts prove that it was being grown for ornament in large gardens in the sixteenth century, from where it presumably escaped along rivers to colonise meadows downstream. Regardless of its status, however, it remains a much-loved and valued component of the British flora and a flagship species for the conservation of floodplain grasslands.

Evidence for multiple colonisations and Wolbachia infections shaping the genetic structure of the widespread butterfly Polyommatus icarus in the British Isles

The paradigm of isolation in southern refugia during glacial periods followed by expansions during interglacials, producing limited genetic differentiation in northern areas, dominates European phylogeography. However, the existence of complex structured populations in formerly glaciated areas, and islands connected to mainland areas during glacial maxima, call for alternative explanations. We reconstructed the mtDNA phylogeography of the widespread Polyommatus Icarus butterfly with an emphasis on the formerly glaciated and connected British Isles. We found distinct geographical structuring of CO1haplogroups, with an ancient lineage restricted to the marginal European areas, including Northern Scotland and Outer Hebrides. Population genomic analyses, using ddRADSeq genomic markers, also reveal substantial genetic structuring within Britain. However, there is negligble mito-nuclear concordance consistent with independent demographic histories of mitochondrial versus nuclear DNA. While mtDNA-Wolbachia associations in northern Britain could account for the geographic structuring of mtDNA across most of the British Isles, for nuclear DNA markers (derived from ddRADseq data) butterflies from France cluster between northern and southern British populations - an observation consistent with a scenario of multiple recolonisation. Taken together our results suggest that contemporary mtDNA structuring in the British Isles (and potentially elsewhere in Europe) largely results from Wolbachia infections, however, nuclear genomic structuring suggests a history of at least two distinct colonisations. This two-stage colonisation scenario has previously been put forth to explain genetic diversity and structuring in other British flora and fauna. Additionally, we also present preliminary evidence for potential Wolbachia-induced feminization in the Outer Hebrides.

Scotland’s heritage of naturalised medicinal plants

Abstract
 Although much has been written about Scottish plants, there has been no Flora of Scotland as such since Hooker’s Flora Scotica of 1821. Instead British Floras and distribution Atlases have been published. When BSBI’s New Atlas of the British and Irish Flora was published in 2002, introduced plants were subdivided into archaeophytes and neophytes for Britain as a whole, but British natives that were considered to be introductions in Scotland were not subdivided. As a result the specifically Scottish archaeophyte heritage has been neglected. Taken together, Sutherland’s Hortus Medicus Edinburgensis 1683 and Sibbald’s Scotia Illustrata 1684 provide a baseline from which to investigate the history of many species now considered to be naturalised introductions in Scotland. This has enabled them to be divided between archaeophytes and neophytes giving perspective to their heritage, particularly that of former medicinal plants. A table of such species is presented with detailed comment.

Inter-simple sequence repeats genetic relationships between populations of Consolida (Ranunculaceae)

In fields like ecology, biogeography, conservation biology, and macroevolutionary theory, species are considered as the fundamental unit of study. Gray (1821), an expert on British flora, regarded the genus Consolida to be a distinct genus based on a single species (C. regalis). Consolida, on the other hand, is believed by some scholars to be a part of Delphinium. There are no reports on the genetic diversity, modes of divergence, or dispersion patterns of the various Consolida species that grow in Iran despite their widespread distribution. Hence, a combination of atomic (ISSR markers) and morphological examinations of 78 increases from seven species of Consolida were conducted. One goal of this work is to determine the diagnostic usefulness of ISSR markers in the delimitation of Consolida species, another is to determine the genetic structure of these taxa, and a third is to look at the relationships between species within these groups. It was discovered in the current research that combining morphological and ISSR data may help identify species. Analysis using AMOVA and STRUCTURE found that the species of Consolida are genetically distinct, yet have some common genes.

Biological Flora of the British Isles: Crataegus monogyna

Abstract This account presents information on all aspects of the biology of Crataegus monogyna Jacq. (Hawthorn) that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the standard framework of the Biological Flora of the British Isles: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characters, herbivores and disease, history and conservation. Crataegus monogyna is native to the British flora, occurring frequently in hedgerows, scrubs, thickets and woodland. It can be found throughout almost all of Europe, on all soils of medium conditions regarding pH value, nutrient and water supply. Crataegus monogyna is a deciduous shrub or rarely a small tree of 2–8 m. Its twigs and branches bear sharp thorns about 1 cm long. Crataegus monogyna is of both ornamental and ecological value. During flowering in May and June, shrubs may appear white through a multitude of flowers, presenting pollen and nectar to a variety of different insects. Starting in August, almost the whole shrub can become dark red with the huge number of small red berries (pomes) produced during fruiting. The fruit are a preferred food for many birds. Although hybridizing freely and frequently with the other native species, Crataegus laevigata (Poir.) DC., the two species are easily recognizable in natural stands in the British Isles. Elsewhere, and with the occurrence of horticultural naturalizations and many intermediate forms of hybrid origin with closely related Crataegus species (especially the similar looking one‐styled species Crataegus rhipidophylla Gand. s.l. and Crataegus × subsphaerica Gand. s.l.) expert knowledge is required to avoid misidentifications and thus inaccurate understanding of frequency and distribution–not only on continental Europe but also increasingly in the British Isles. Identification in the field is further complicated by inbreeding of horticultural stock, which suffers from a myriad of descriptions and given names at different hierarchical levels. Cultivars are commonly planted in hedges and along roadsides or for ornamental purposes. The origin of this stock is not always known, so genetic exchange with the natural populations may lead to introgression and thus genotypes that are more adapted than the local genotypes in a changed environment.

What plant is that? Tests of automated image recognition apps for plant identification on plants from the British flora.

There has been a recent explosion in development of image recognition technology and its application to automated plant identification, so it is timely to consider its potential for field botany. Nine free apps or websites for automated plant identification and suitable for use on mobile phones or tablet computers in the field were tested on a disparate set of 38 images of plants or parts of plants chosen from the higher plant flora of Britain and Ireland. There were large differences in performance with the best apps identifying >50 % of samples tested to genus or better. Although the accuracy is good for some of the top-rated apps, for any quantitative biodiversity study or for ecological surveys, there remains a need for validation by experts or against conventional floras. Nevertheless, the better-performing apps should be of great value to beginners and amateurs and may usefully stimulate interest in plant identification and nature. Potential uses of automated image recognition plant identification apps are discussed and recommendations made for their future use.

Microhypnum sauteri (Schimp.) Jan Kučera & Ignatov in West Sutherland, new to the British flora

ABSTRACT Introduction. The tiny moss Microhypnum sauteri is widely distributed in Europe being recorded from 14 countries, but it seems to be relatively uncommon everywhere and is on the Red List in seven of these countries. The sites in Norway are the closest populations to this new find in Scotland. Methods. A specimen was collected during a visit to Assynt in West Sutherland in April 2019, during a survey of populations of Amblyodon dealbatus and Encalypta alpina, and subsequently identified as Microhypnum sauteri. Results. Micrcohypnum sauteri is reported from the limestone at Inchnadamph in West Sutherland, new to the British flora. The species and its habitat are described and comments made on its ecology and European distribution. Conclusions. The site where Micrcohypnum sauteri was found has a number of other montane calcicole species and M. sauteri is most likely to be native here. Given its small size and the fact that it has been overlooked at such a well-known site, it seems quite possible that it could occur on calcareous rocks in the mountains elsewhere in Scotland, some other possible locations being the high limestone in the Alder Forest and in the Glenshee area and perhaps on the calcareous schist on Ben Lawers.

The genus Oncophorus in Britain and the addition of O. integerrimus Hedenäs to the British flora

ABSTRACT Introduction. Currently there are two species of Oncophorus recorded in Britain O. virens (Hedw.) Brid. and O. wahlenbergii Brid., both uncommon species of wet, upland sites which are at least moderately calcareous. In a revision of Scandinavian material, Hedenäs divided O. virens into two species, O. virens and O. integerrimus, and described two further species, O. elongatus and O. demetrii previously referred to O. wahlenbergii. Methods. Herbarium specimens of all British Oncophorus species from the Royal Botanic Garden Edinburgh (E) the National Museum of Wales, Cardiff (BBSUK, NMW) and the Natural History Museum (BM), plus material from the author’s own herbarium were examined and re-determined using Hedenäs’ descriptions. Results. None of the vouchers checked proved to be either O. elongatus or O. demetrii but in addition to O. virens and O. wahlenbergii some of the vouchers belonged to O. integerrimus so this species is added to the British list. The key features for distinguishing the three species are described. Conclusions. In Britain all three species have similar habitat preferences, usually occurring above 600 m and reaching as high as 1000 m a.s.l. on Ben Lawers. They most frequently occur in a turf, often with other bryophytes and sedges, in flushed ground at the edge of springs or below crags, where the bedrock is at least moderately calcareous and most sites are associated with calcareous schist or limestone. There is little change in the pattern of distribution as a result of the re-determinations and Oncophorus virens remains the only English species.

Inequality in plant diversity knowledge and unrecorded plant extinctions: An example from the grasses of Madagascar

Societal impact statementPlants are essential for all life, providing the infrastructure and energy for our ecosystems. A recent report indicates that more than 500 plant species are already presumed extinct and many more could have been lost without anyone being aware, especially in species‐rich areas with high levels of human impact, and where botanical knowledge is poor. Inequality in the availability and accessibility of biodiversity data, professional expertise, and funding interact to produce chronic differences in knowledge between countries. Here, we illustrate this using an example from Madagascar. Understanding these knowledge inequalities will strengthen our ability to improve the situation for people as well as for plants.SummaryIn order to understand geographic differences in our knowledge of plant extinction, species occurrence knowledge is compared for the grasses (Poaceae) of Madagascar and the British Isles. Poaceae are a useful model system for exploring extinction because they are globally diverse and present interesting characteristics compared with plants as a whole: grasses have a similar species description curve and percentage assessed as threatened, but they have broader and more continental distribution ranges.Historical and current factors affecting the documentation of the Malagasy and British floras are reviewed with regard to science funding, human capital, accessibility, and existing records. Knowledge of Poaceae is compared in the light of these constraints. Global patterns of grass diversity are examined and future extinction rates for Malagasy grasses are estimated.Multiple factors interact to shape a set of constraints on species distribution knowledge. The flora of Madagascar has been described largely by foreigners, science funding is external, and Malagasy botanists face difficult challenges. Spatial data for Madagascar are more limited and less even. We demonstrate that unrecorded extinctions are more likely among Malagasy than British and Irish grasses: they were described later, have smaller ranges, and are more threatened. It is possible that extinction rates of Malagasy grasses will increase tenfold in the next century.Differences in our knowledge of the Malagasy and British floras are long‐standing, deep, and perpetuated by numerous modern‐day factors. We urge researchers to understand and acknowledge these differences, and we provide recommendations for future work.

Three poisonous plants (Oenanthe, Cicuta and Anamirta) that antagonise the effect of γ-aminobutyric acid in human brain.

Although we are familiar with common British plants that are poisonous, such as Atropa belladonna (deadly nightshade) and Aconitum napellus (monkshood), the two most poisonous plants in the British Flora are Oenanthe crocata (dead man's fingers) and Cicuta virosa (cowbane). In recent years their poisons have been shown to be polyacetylenes (n-C2H2). The plants closely resemble two of the most common plants in the family Apiaceae (Umbelliferae), celery and parsley. Unwittingly, they are ingested by naive foragers and death occurs very rapidly. The third plant Anamirta derives from South-East Asia and contains a powerful convulsant, picrotoxin, which has been used from time immemorial to catch fish, and more recently to poison Birds of Paradise. All three poisons have been shown to block the γ-aminobutyric acid (GABA) system in the human brain that normally has a powerful inhibitory neuronal action. It has also been established that two groups of sedative drugs, barbiturates and benzodiazepines, exert their inhibitory action by stimulating the GABA system. These drugs are the treatments of choice for poisoning by the three vicious plants.

Hybridisation and introgression in British Helosciadium (Apiaceae).

Reticulation between Helosciadium repens (Jacq.) W.D.J. Koch and H. nodiflorum (L.) W.D.J. Koch (Apiaceae) has been the source of much speculation, but until now supporting evidence has remained largely anecdotal. In the current study inter-specific hybridisation and introgression between the two species was confirmed using DNA barcoding. The parentage of three putative hybrids collected from Port Meadow, Oxfordshire (UK) was determined using a maternally-inherited chloroplast marker (rps16-trnK) and two biparentally-inherited nuclear markers (LEAFYi2, ITS). Two of the individuals are early-generation hybrids between H. repens and H. nodiflorum, F1 or otherwise, while the third is most likely a backcross to H. repens. These individuals are the first confirmed hybrids/hybrid derivatives between the two parental species, and represent a new addition to the British flora. The hybrids closely resemble H. nodiflorum var. longipedunculatum F.W. Schultz, and in our view should be treated as H. × longipedunculatum (F.W. Schultz) Desjardins.

John Adams FLS of Pembroke (1769–1798): a forgotten Welsh naturalist and conchologist

John Adams was a member of a long line of landed gentry from Pembrokeshire, Wales. At a young age, he became a Fellow of the Linnean Society and read four papers before his untimely death by drowning at the age of 29. He described 53 invertebrate species as new to science, mostly from small molluscan shells, but he should be regarded as a naturalist, not a shell collector. He read mathematics at Cambridge University and seems to have relied heavily on his library and social connections to develop his expertise in natural history. Although never publishing on botany, the annotations in his botanical books and his connections with John Symmons and James Edward Smith show him to be competent with the British flora.

Hygrohypnum subeugyrium (Renauld & Cardot) Broth. (Hypnales), a neglected British moss, with a note on its occurrence in the Himalayas

ABSTRACTHygrohypnum subeugyrium was first reported for Britain in 1976, but it has been ignored in subsequent British floras and identification guides. Morphologically it is a distinct species. New localities were discovered during a meeting of the British Bryological Society in Scotland in 2017. A subsequent revision of herbarium material has shown that H. subeugyrium is widely distributed in Scotland and occurs southwards to a few localities in England and Wales. Its extra-European distribution is extended to include the Himalayan region (Sikkim and Yunnan). It is described and illustrated, and its diagnostic characters are discussed.

Chronicling the discovery of the British and Irish native floras – Richard Pulteney's overlooked contribution

Until 1897, when William Clarke produced his First records of British flowering plants, there was no publication where one could see the date and source of the discovery of all of the native plants in Britain and Ireland. Two manuscripts were traced in the library of the Natural History Museum, London, which are in the hand of Richard Pulteney, an apothecary and physician, and also author of works on Linnaeus and the history of botany in Britain. The first of these manuscripts, based on the second edition of Hudson's Flora Anglica (1778), traces each plant described in that work back to the earliest authorities; the second lists a single authority, as the ‘first describer or discoverer’ of each plant. Although Pulteney was handicapped by not having access to all of the pre-1640 literature, these manuscripts nevertheless represent an important contribution to the discovery of our flora, pre-dating, as they do, the work of Clarke by a century.

The first Pleistocene fossil records of Urtica kioviensis Rogow. (Urticaceae) and Potamogeton sukaczevii Wieliczk. (Potamogetonaceae) in the British Isles

Seeds of the extant Urtica kioviensis Rogow. (Urticaceae) and endocarps of the extinct Potamogeton sukaczevii Wieliczk. (Potamogetonaceae) were recorded in diverse plant macrofossil assemblages recovered from organic sediments exposed during excavations at Saham Toney, Norfolk, UK. Aminostratigraphical data show the sediments were deposited during the Ipswichian (Last Interglacial) Stage. Palynological data indicates deposition during the Carpinus pollen zone of the Ipswichian Stage—the latter part of pollen zone Ip IIb and Ip III. The records are noteworthy not only because they are the first in the British Pleistocene but also because of the geographical occurrences of these two species. Urtica kioviensis is absent from the British flora today and has a modern range in central and eastern Europe (only extending as far west as north–east Germany and Denmark), while the extinct Potamogeton sukaczevii has only been recovered from Late Pleistocene sediments in Belarus, Lithuania, Poland and western Russia. The presence of U. kioviensis along with other exotic species to the British Isles (e.g. Najas minor L. and Salvinia natans L., which today have central and southern ranges in Europe and in the case of S. natans occurs on other continents) may point to more continental conditions or warmer summer conditions during the second half of the Ipswichian Stage in southern Britain. No modern analogues occur in Britain for the assemblages recovered from Saham Toney. Evidence of colder winters or at least warmer summers at the time of deposition does not support the view that sea-level peaked in the Carpinus zone of the Eemian Stage (correlated with the Ipswichian Stage) associated with increased oceanicity. Southern Britain would have been under the influence of the Atlantic Ocean and a degree of oceanicity is supported by the presence of two thermophilous taxa, Hedera and Ilex, in the pollen spectra from Saham Toney. Alternative explanations for the presence of these exotic species are that they were tolerating mild winters and cooler summers at the time of deposition or exploiting suitable micro-environments. The distribution of P. sukaczevii is probably an artefact of the distribution of expertise in the identification of Potamogeton fossil endocarps rather than having any palaeogeographic or palaeoclimatic significance. It is an extinct ancestor of the extant P. maackianus A. Benn, an eastern Asian pondweed. Its discovery in Britain encourages a reassessment of plant macrofossil assemblages from western Europe, which may lead to a consideration of the relationship between the Late Pleistocene vegetation of Europe and eastern Asia.

Biological Flora of the British Isles:Phragmites australis

SummaryThis account presents comprehensive information on the biology ofPhragmites australis(Cav.) Trin. ex Steud. (P. communisTrin.; common reed) that is relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the standard framework of theBiological Flora of the British Isles: distribution, habitat, communities, responses to biotic factors and to the abiotic environment, plant structure and physiology, phenology, floral and seed characters, herbivores and diseases, as well as history including invasive spread in other regions, and conservation.Phragmites australisis a cosmopolitan species native to the British flora and widespread in lowland habitats throughout, from the Shetland archipelago to southern England. It is widespread throughout Ireland and is native in the Channel Islands. Native populations occur naturally in temperate zones and on every continent except Antarctica. Some populations in Australia and North America have been introduced from elsewhere and have become naturalized, and in North America, some of these are known to be invasive where they compete with native local populations ofP. australis. Typical habitats in Britain range from shallow still water along waterbody edges to marshlands, saltmarshes and drier habitat on slopes up to 470 m above sea level. Additional habitats outside Britain are springs in arid areas, riverine lowlands (−5 m above sea level) and groundwater seepage points up to 3600 m above sea level. Although it occurs on a wide range of substrates and can toleratepHfrom 2·5 to 9·8, in Britain it preferspH>4·5 and elsewhere it thrives in mildly acidic to mildly basic conditions (pH5·5–7·5). The species plays a pivotal role in the successional transition from open water to woodland.Phragmites australisis a tall, helophytic, wind‐pollinated grass with annual shoots up to 5 m above‐ground level from an extensive system of rhizomes and stolons. A single silky inflorescence develops at the end of each fertile stem and produces 500–2000 seeds. The plant is highly variable genetically and morphologically.Expansion of established populations is mainly through clonal growth of the horizontal rhizome system and ground‐surface stolons, while new populations can establish from rhizomes, stem fragments and seeds. Shoots generally emerge in spring, with timing determined primarily by physiology that is mediated by external conditions (e.g. local climate including frost).Many populations in the British Isles have experienced some decline over the past two decades and there is concern that there might be further losses along the east coast as sea level rises. There have recently also been localized expansions, especially in highly modified habitats, whereP. australisreedbeds have been planted as wildlife habitat, rehabilitated mineral and gravel beds, and bioremediation filter beds for industrial and transport infrastructure. Native populations outside Britain also demonstrate both types of trend: they are declining in many parts of Western Europe and North America, yet also colonize many disturbed, ruderal habitats (e.g. the edges of agricultural fields and motorways) throughout its native and non‐native range and can form ‘weedy’ monodominant populations (e.g. in Australia and China).