Calliergon cordifolium

{{Short description|Species of moss}}

{{Speciesbox

| image = Calliergon cordifolia resize.jpg

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| genus = Calliergon

| species = cordifolium

| authority = (Hedw.) Kindb.{{cite web|url= http://plants.usda.gov/java/profile?symbol=CACO70|title= Calliergon cordifolium (Hedw.) Kindb.|publisher= United States Department of Agriculture|access-date= 16 June 2012}}

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Calliergon cordifolium is a species of moss in the Calliergonaceae family,{{cite book |last1=Goffinet |first1=B. |first2=W. R. |last2=Buck |first3=A. J. |last3=Shaw |year=2008 |chapter=Morphology and Classification of the Bryophyta |pages=55–138 |editor-last1=Goffinet |editor-first1=B. |editor-first2=J. |editor-last2=Shaw |title=Bryophyte Biology |edition=2nd |location=New York |publisher=Cambridge University Press |isbn=978-0-521-87225-6 |chapter-url=https://books.google.com/books?id=te0fAwAAQBAJ&pg=PT108}}{{cite web |last1=Goffinet |first1=B. |first2=W.R. |last2=Buck |title=Classification of extant moss genera |website=Classification of the Bryophyta |url=http://bryology.uconn.edu/classification/#BRYIDAE |access-date=1 May 2020}} commonly known as the calliergon moss (though this name refers to the genus Calliergon generally) or heart-leaved spearmoss.{{cite book|last=Edwards|first=Sean R.|date=2012|title=English Names for British Bryophytes|location=Wootton, Northampton|publisher=British Bryological Society|isbn=978-0-9561310-2-7|issn=0268-8034|series=British Bryological Society Special Volume|volume=5|edition=4th}} The species is abundant in the right habitat, and grows in marshes and wet woodland,{{cite book|chapter= Calliergon cordifolium|chapter-url= http://www.bbsfieldguide.org.uk/sites/default/files/pdfs/mosses/Calliergon_cordifolium.pdf|author= Tom Blockeel|editor= I. Atherton|editor2= S. Bosanquet|editor3= M. Lawley|title= Mosses and Liverworts of Britain and Ireland|publisher= British Bryological Society|page= 719|year=2010|isbn= 9780956131010}} especially woodland of alder (Alnus) or willow (Salix),{{cite book|title= Bryophytes of the Pleistocene: The British Record and Its Chorological and Ecological Implications|author=James Holmes Dickson|date=February 1973|page=145|publisher=Cambridge University Press|isbn=9780521085762}} as well as around streams, ditches and pools. The species grows in tufts among other moss species. Calliergon cordifolium requires a wet environment to grow, and often grows completely submerged in water. It typically prefers lowland, but has been recorded as high as {{convert|910|m|yards}} above sea level in Inverness, Scotland. The species has a circumpolar Boreo-temperate distribution. It is found throughout Europe (including north, into the Arctic Circle - Svalbard, the Faeroe Islands, Iceland and Greenland - and east into the Caucasus). It has been recorded in north and central Asia, as well as Turkey and Japan, throughout North America and in New Zealand.{{cite book|author=A. J. E. Smith|author2=Ruth Smith|name-list-style=amp|title= The Moss Flora of Britain and Ireland|publisher= Cambridge University Press|year= 2004|page=787|isbn=9780521546720}}

Calliergon cordifolium is a medium-sized to large moss with erect, green shoots. The shoots can reach up to {{convert|15|cm|in}}, with egg-shaped leaves from {{convert|2|to|2.5|mm|in}} wide. The leaves extend outwards, away from the stem. Towards the base, the leaves take on a heart shape, while, at the tip, they are rounded. The spore-bearing capsules are rarely seen, and are encountered only in spring or summer. The spores measure 10 to 16 micrometres across. Calliergon cordifolium can be mistaken for similar species, including Calliergon giganteum, Calliergonella cuspidata, Straminergon stramineum and Pseudocalliergon trifarium.