{{Short description|Species of flowering plant}} {{Speciesbox |name = Dwarf birch |image = Betula nana0.jpg |status = LC |status_system = IUCN3.1 |status_ref = <ref name="iucn status 19 November 2021">{{cite iucn |author=Stritch, L. |date=2014 |title=''Betula nana'' |volume=2014 |article-number=e.T194495A2341542 |doi=10.2305/IUCN.UK.2014-3.RLTS.T194495A2341542.en |access-date=19 November 2021}}</ref> |genus = Betula |parent = Betula subg. Chamaebetula |species = nana |authority = [[Carl Linnaeus|L.]] }}

'''''Betula nana''''', the '''dwarf birch''',<ref>{{cite book|url=https://books.google.com/books?id=lOa9CgAAQBAJ&pg=PA12|title=Routledge Handbook of Forest Ecology|editor=Kelvin S.-H. Peh|editor2=Richard T. Corlett|editor3=Yves Bergeron|publisher=[[Routledge]]|year=2015|page=12|isbn=978-0-415-73545-2}}</ref> is a species of [[birch]] in the family [[Betulaceae]], found mainly in the [[tundra]] of the [[Arctic region]]. [[File:Betukananabereza.jpg|thumb|Specimen at 1000m]]

==Description== It is a [[monoecious]], [[deciduous]] shrub growing up to {{convert|1|–|1.2|m}} high. The bark is non-peeling and shiny red-copper colored.<ref>Ewing, Susan. ''The Great Alaska Nature Factbook''. Portland: Alaska Northwest Books, 1996.</ref> The [[leaf|leaves]] are rounded, {{convert|6|-|20|mm}} diameter, with a bluntly toothed margin. The leaves are a darker green on their upper surface. Leaf growth occurs after snow melt and become red in autumn.

The wind-pollinated fruiting [[catkin]]s are erect, {{convert|5|–|15|mm}} long and {{convert|4|–|10|mm}} broad.

==Distribution== ''Betula nana'' is native to arctic and cool [[temperate]] regions of [[Greenland]], [[Iceland]], northern [[Europe]], northern [[Asia]] and northern [[North America]] and it will grow in a variety of conditions. Outside of far northern areas, it is usually found growing only in [[mountain]]s above {{convert|300|m}}, up to {{convert|835|m}} in [[Great Britain]] and {{convert|2200|m}} in the [[Alps]]. Its northern range limit is on [[Svalbard]], where it is confined to favourable sites. In the UK ''Betula nana'' is at its southern range limit, with many populations having declined significantly in recent decades.<ref>{{cite journal|author=Borrell, James S.|author2=Wang, Nian|author3=Nichols, Richard A.|author4=Buggs, Richard J. A.|date=15 August 2018|title=Genetic diversity maintained among fragmented populations of a tree undergoing range contraction|journal=Heredity|volume=121|issue=4|pages=304–318|doi=10.1038/s41437-018-0132-8|pmid=30111882|pmc=6134035|issn=0018-067X|oclc=888447574}}</ref> In southern Sweden the occurrence of ''Betula nana'' in [[Sund, Ydre|Sund]], [[Ydre]] is deemed a [[glacial relict]].<ref name=Hellgren1960>{{cite book |last1=Hellgren |first1=George |title=Ydre-Boken |date=1960 |location=Linköping |pages=86–91|chapter=Något om växtligheten i Ydre|editor-last=Filén|editor-first=Thure|language=Swedish}}</ref>

It generally favours wet, but well-drained sites, with a nutrient-poor, acidic soil that can be xeric and rocky. ''B. nana'' has a low tolerance for shade.

==Ecology== There are two [[subspecies]]: *''Betula nana'' subsp. ''nana''. [[Canada]] ([[Baffin Island]]), Greenland, northern Europe (south to the Alps at high altitudes), northwestern Asia. Young twigs hairy, but without resin; leaves longer (to 20&nbsp;mm), usually as long as broad. *''Betula nana'' subsp. ''exilis''. Northeastern Asia, northern North America ([[Alaska]], Canada east to [[Nunavut]]). Young twigs hairless or with only scattered hairs, but coated in resin; leaves shorter (not over 12&nbsp;mm long), often broader than long.

==Genome== The genome of ''B. nana'' has been sequenced.<ref>{{cite journal|author=Wang N.|author2=Thomson M.|author3=Bodles W.J.A.|author4=Crawford R.M.M.|author5=Hunt H.V.|author6=Featherstone A.W.|author7=Pellicer J.|author8=Buggs R.J.A.|title=Genome sequence of dwarf birch (Betula nana) and cross-species RAD markers|journal=Mol. Ecol.|year=2013|volume=22|issue=11|pages=3098–3111|doi=10.1111/mec.12131|pmid=23167599|s2cid=206179485}}</ref>

==References== {{Reflist}}

==External links== {{Wikispecies|Betula nana}} {{Commons}} *Trees for Life: [https://web.archive.org/web/20051215203906/http://www.treesforlife.org.uk/tfl.dwarf_birch.html Species profile] and [https://web.archive.org/web/20050829024350/http://www.treesforlife.org.uk/tfl.dwarf_birch_ref.html Reference list] *[http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=233500254 Flora of North America: ''Betula nana''] *[http://linnaeus.nrm.se/flora/di/betula/betul/betunanv.jpg ''Betula nana'' Distribution map] *[https://web.archive.org/web/20051124171141/http://instaar.colorado.edu/AAAR/volume34/34-4abs.html#cgp Conservation Genetics and Population History of Betula nana etc., in Svalbard] *[https://web.archive.org/web/20180828211003/http://www.birchgenome.org/ Dwarf birch genome website] *[https://web.archive.org/web/20131111191459/http://www.aber.ac.uk/en/ibers/studying/current/linnaeus/literature/betula-nana/ Literature arising from the Expedition » Betula nana]

[[Image:Betula nana upernavik kujalleq 2007-07-25 1.jpg|thumb|left|Betula nana photographed north of the village of [[Upernavik Kujalleq]], north-east of the mountain Kingigtoq, western Greenland]] {{Taxonbar|from=Q157628}} {{Authority control}}

[[Category:Betula|nana]] [[Category:Alpine flora]] [[Category:Flora of Europe]] [[Category:Flora of Siberia]] [[Category:Flora of Subarctic America]] [[Category:Flora of the Russian Far East]] [[Category:Flora of Western Canada]] [[Category:Plants described in 1753]] [[Category:Botanical taxa named by Carl Linnaeus]]