|Lysichiton americanus (Araceae – American skunk cabbage)
Why Addition of Lysichiton americanus to the EPPO Alert List was suggested by the BBA and the Federal Agency for Nature Conservation in Germany (Klingenstein & Schrader, 2004). L. americanus originates from North America but it is now found in several European countries. Its invasiveness has clearly been demonstrated in Germany and United Kingdom during the last 20-30 years, as well as its negative impact on biodiversity.
Description L. americanus is a herbaceous, perennial plant. It can be terrestrial, semi-aquatic, or aquatic. Plants are generally erect, from relatively short to 1.5 m high. One adult plant may cover 1 m² ground. Growth is slow but L. americanum can build old (> 80 years) and dense populations. It has large tobacco-like leaves (40-70 cm up to 1.5 m), leathery in texture and with thick veins. Inflorescences (1 or 2 per plant) appear between March and May, before the leaves and they have an unpleasant smell which is a combination of skunk (hence the name!), carrion and garlic. They attract flies, midges and beetles (e.g. adults of Pelecomalium testaceum (Coleoptera: Staphylinidae) which feed on pollen and use inflorescences as mating sites). The inflorescence is a showy and bright yellow spathe (8 to 45 cm high), surrounding a spadix which bears small, green flowers. After flowering, fruits (150-350 green berries) develop along the spadix. Each berry usually carries 2 grey-brown to red-brown seeds (5-11 mm). L. americanus also has thick, fleshy rhizomes (up to 30 cm long and with a diameter of 2.5-5 cm).
Pictures can be viewed on Internet:
Distribution Lysichiton americanus originates from the eastern part of North America. In the last edition of Flora Europaea (Tutin et al. 1980), L. americanus was only reported from the British Isles including Ireland. Since then, it has been recorded from several other European countries.
North America: Canada (Western), USA (Alaska, California, Idaho, Montana, Oregon, Washington).
EPPO region: Ireland (24 sites), Germany (4 sites), Norway (2 sites in south Norway near Arendal), Sweden (29 sites in south and central regions), Switzerland (100 plants have been observed since May 2003 at 1 site in the protected area of Meienmoos near Burgdorf, canton of Berne), United Kingdom (including Northern Ireland – recorded on 174 sites, cultivated since 1901 and first reported in the wild in 1947).
In Germany, several thousands of huge plants (>80 cm) and many thousands of small plants have been found in the Taunus mountains near Frankfurt since the 1980s. Plants have been reported in Brexbachtal near Koblenz since the beginning of the 1990s. 17 plants have also been observed in swamp forests near Mühlheim/Ruhr since 2002 and 10 plants at Pillebachtal near Düsseldorf since 2004. In Sweden, L. americanus was introduced around 1975 as an ornamental plant. It is now found in bogs and moist forests where it propagates and seems well established (e.g. rivulets Vinån and Fylleån in the province of Halland, Tveta in the province of Södermanland and in the province of Östergötland).
Habitat Swamps, wet woods and shrubs, along streams and riverbanks, lakesides, ponds, in boggy and other wet areas; from 0-1400 m altitude. L. americanus can grow on various types of soils, from light (sandy) to heavy (clay) with a wide range of pH (from acid to basic), but it requires wet soils. It can stand shade or full light, and cold temperatures (at least -15°C).
Damage L. americanus significantly reduces biodiversity. It is one of the few alien plant species in Europe that is naturalized in natural habitats, especially swamp forests. After some years, its huge leaves build a dense layer excluding light from native species which are usually not adapted to extreme darkness. Swamp forests and associated wetlands are rare and fragile ecosystems, already endangered by land use practice. They contain many endangered species of national red lists. The displacement and local extinction of rare species of mosses (like Aulacomnium palustre and various Sphagnum species) and vascular plants (Carex echinata, Viola palustris, and orchids) by L. americanum has been shown. All studies and records from the above-listed EPPO countries show that L. americanus can produce viable offspring on the sites where it is present. Young plants spread slowly but continuously, gradually displacing the natural vegetation. As an example, populations discovered in the Taunus mountains (Germany) increased from ‘a few plants’ in the 1990s to several hundreds in 2004. From the years of the first records to 2000, 47 new stands have been recorded.
In Switzerland, the species is included on the national black list of species, where negative ecological impacts have been documented, and which are problematic for nature conservation and for human health, and control measures started in 2003. In Germany it is included in the national Internet Handbook of invasive plants and control measures began in the Taunus region. It is regarded as a weed by the Global Compendium of Weeds.
Dispersal Under natural conditions most seeds fall to the ground with the whitered spadix. They can be transported further by running water. In their native range long distance dispersal is ensured by animals (small rodents like squirrels, birds, but also bears) eating the berries.
In nature, regeneration mainly occurs by seeds, but since artificial propagation for gardening is mainly done by dividing the rhizome, fragmentation of stems or rhizome may be an important vector for distribution (e.g. with machines and vehicles used for sylviculture).
Pathway Plants for planting are the main pathway for L. americanus. It is grown in many botanical gardens (e.g. in Germany) and more and more favoured by gardeners as a plant for ponds and other wet places, because of its striking inflorescences and robustness. The Royal Horticultural Society Floral Committee (GB) awarded L. americanus an Award of Garden Merit: ‘Over the years the plants have seeded themselves freely and now make a fantastic display covering the full length of the stream and beyond.’ Pathways of secondary release may be soil and water containing viable stem fragments or seeds.
Possible risks All available data clearly demonstrates the risks to biological diversity. The pathways indicate that the plant will spread slowly but continuously in future. Therefore, early detection is important, and rapid measures should be taken at all newly recorded stands. Control measures are existing and efficient. Due to the sensitive ecosystems where L. americanus occurs, chemical methods are not appropriate, but only mechanical control measures. Plants have to be lifted with their entire rhizomes and roots. If this is not possible, the rhizome has to be cut as deep as possible. Measures have to be repeated on the remaining plants and success has to be monitored for at least 5 years. The high invasiveness but the infrequent occurrence at new sites and slow growth at the reported sites renders measures at the same time necessary and feasible.
Source(s) Klingenstein, F.; Schrader, G. (2004) Draft data sheet on Lysichiton americanus (unpublished document).
Tutin, T.G.; Heywood, V.H.; Burges, N.A.; Valentine, D.H. [eds.] (1980) Flora Europaea Volume 5: Alismataceae to Orchidaceae. Cambridge University Press, 476 p.
Biologische Station Westliches Ruhrgebiet (DE). Lysichiton americanus Hultén & St. John (Araceae) in Duisburg und Mülheim an der Ruhr. http://www.bswr.de/Flora/Lysichiton/Lysichiton01.htm
Botanical garden information system (for Germany) http://www.biologie.uni-ulm.de/systax/infgard/bg_qfrme.html
Botany in Norway (Botanisk informasjon på Internett) http://www.museumsnett.no/naturmuseum/tusenaarshagen/lysichiton_americanus.shtml
Canton de Berne, Suisse. http://www.be.ch/cgi-bin/frameset.exe?http://www.vol.be.ch/lanat/natur/neo.html
Den virtuella floran (http://linnaeus.nrm.se/flora/mono/ara/lysic/lysiame.html: fact sheet about Lysichiton americanus and its naturalisation in Sweden)
Flora of North America. http://www.efloras.org/object_page.aspx?object_id=10953&flora_id=1
Flora of Northern Ireland. http://www.habitas.org.uk/flora/species.asp?item=2350
FloraWeb (German flora)
Global Compendium of Weeds http://www.hear.org/gcw/html/autogend/species/11956.HTM
Johann Wolfgang Goethe-Universität Frankfurt am Main (DE) Projekt Stinktierkohl. http://www.uni-frankfurt.de/fb15/botanik/Projekt-Stinktierkohl/Stinktierkohl.htm
Royal Horticultural Society (UK) (http://www.rhs.org.uk/gardens/harlowcarr/archive/harlowcarrpomapril.asp)
Swiss black list of invasive plants. (http://www.cps-skew.ch/english/black_list.htm
Swedish Environmental Protection Agency (http://www.naturvardsverket.se/dokument/natur/migrera/tartlist.pdf: a list of alien species of Sweden)
Swedish Biodiversity Centre (http://www.cbm.slu.se/pdf/regeringsuppdrag/frammandearter/I-Grandin.pdf : article including Lysichiton as an (potentially?) invasive plant in Sweden)
USDA Natural Resources Conservation Service (Plant Profile for Lysichiton americanus) http://plants.usda.gov
EPPO RS 2004/156
Panel review date -2005-03 Entry date 2004-10