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Persicaria maculosa (syn. Polygonum persicaria) is an annual plant in the buckwheat family, Polygonaceae. Common names include lady's thumb,<ref>{{#if:20915 | {{#invoke:template wrapper|wrap|_template=cite web|_exclude=id,ID,taxon
| url = https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=20915 | title = Polygonum persicaria | publisher = Integrated Taxonomic Information System }}
| Template:Citation error }}</ref> spotted lady's thumb, Jesusplant, and redshank.<ref name=BSBI07>Template:BSBI 2007</ref><ref name=grin>Template:GRIN</ref> It is widespread across Eurasia from Iceland south to Portugal and east to Japan.<ref>Altervista Flora Italiana, Persicaria maculosa Gray includes photos and European distribution map</ref><ref name=jing>Flora of China, Polygonum persicaria Linnaeus, 1753. 蓼 liao </ref> It is also present as an introduced and invasive species in North America, where it was first noted in the Great Lakes region in 1843 and has now spread through most of the continent.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name=NatureServe/><ref>Biota of North America Program 2014 state-level distribution map</ref>
DescriptionEdit
Persicaria maculosa is an annual herb up to Template:Convert tall,<ref name=":0">Template:Cite book</ref> with an erect, rather floppy stem with swollen joints. The leaves are alternate and almost stalkless. The leaf blades often have a brown or black spot in the centre and are narrowly ovate and have entire margins. Each leaf base has stipules which are fused into a stem-enclosing sheath that is loose and fringed with long hairs at the upper end. The inflorescence is a dense spike. The perianth of each tiny pink flower consists of four or five lobes, fused near the base. There are six stamens, two fused carpels and two styles. The fruit is a shiny black, three-edged achene. This plant flowers from July to September in the temperate Northern Hemisphere.<ref name=jing/><ref name=NatureGate>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>Flora of North America, Persicaria maculosa Gray, 1821. Spotted lady's-thumb, redshank, renouée persicaire </ref>
TaxonomyEdit
The species was first described, as Polygonum persicaria, by Carl Linnaeus in 1753.<ref name=IPNI_696241-1/> It was first successfully transferred to the genus Persicaria by Samuel Frederick Gray in 1821, under the name Persicaria maculosa.<ref name=IPNI_206340-2/> The name "Persicaria persicaria" cannot be used because tautonyms – binomial names that use the same word for both the genus and the species epithet – are prohibited by the International Code of Nomenclature for algae, fungi, and plants, and a replacement name (nomen novum) must be used.<ref>International Code of Nomenclature for algae, fungi, and plants (Melbourne Code) see section 23.4</ref> For this reason the transfer of the species to Persicaria by John Kunkel Small in 1903, which used the tautonym, is invalid.<ref name=IPNI_190848-2/>
Distribution and habitatEdit
Persicaria maculosa is native to Europe and Asia, where it can be mistaken for Polygonum minus. The latter has narrower leaves, usually less than 1 cm wide. It has been introduced to North America and is naturalised throughout the mainland continent,<ref>USDA</ref> growing along roadsides, riverbanks, and on fallow ground. In the United States, it is very similar to Pennsylvania smartweed, but redshank has a fringe of hairs at the top of the ochrea, something which Pennsylvania smartweed lacks. The species has also been found in New Zealand and Australia.<ref>Atlas of Living Australia, Persicaria maculosa Gray, Jesus Plant</ref><ref>IUCN Red List of Threatened Species, Persicaria maculosa</ref>
EcologyEdit
In the British Isles, this plant is a weed, without natural habitat, and always associated with human activity.<ref>Template:Cite journal</ref> It likes moist soils, particularly rich ones, and acid peaty loams.<ref>Template:Cite journal</ref> It does not like lime, and liming is cited as a means to fight it.<ref>Template:Cite journal</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
Cultivation and usesEdit
Persicaria maculosa contains persicarin and tannins. The young leaves may be eaten as a leaf vegetable.<ref name=":0" /> It is often seen as a weed and rarely cultivated. A yellow dye can be produced from this plant with alum used as a mordant.