Calliergon giganteum

{{Short description|Species of moss}}

{{speciesbox

| image = Calliergon giganteum.jpeg

| image_alt =

| image_caption =

| genus = Calliergon

| species = giganteum

| authority = (Schimp.) Kindb.

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Calliergon giganteum, the giant 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=4}} giant calliergon moss,{{PLANTS|id=CAGI70|taxon=Calliergon giganteum|accessdate=4 February 2016}} or arctic moss, is an aquatic plant found on lake beds in tundra regions. It has no wood stems or flowers, and has small rootlets instead of roots.

Calliergon giganteum survives in the cold climate by storing nutrients to be used in the formation of new leaves in the spring. It can survive with less available nitrogen than any other known plant.{{cite web | url= https://www.arctic.uoguelph.ca/cpl/arcticnews/updates/slowmoss.htm | archive-url= https://web.archive.org/web/20070820230336/https://www.arctic.uoguelph.ca/cpl/arcticnews/updates/slowmoss.htm | url-status= dead | archive-date= 2007-08-20 | last= anonymous | title= Amazing Arctic Moss | access-date= September 30, 2003 }} It is one of about 2000 plant species on the tundra, most of which are mosses and lichens. The plant is eaten by migrating animals such as birds. The ground cover of Calliergon giganteum in the arctic has a warming effect which other plants benefit from.

"Calliergon giganteum" grows to be about 8 cm tall. The leaves live for "at least four years", possibly the longest living of any moss.

Calliergon giganteum prefers hydric environments, growing best in wet and humid conditions. For photosynthesis, the optimum water content is 1500-1700% of the moss's dry weight.{{Cite journal |last=Ueno |first=Takeshi |last2=Kanda |first2=Hiroshi |date=2006 |title=Photosynthetic response of the arctic semi-aquatic moss Calliergon giganteum to water content |url=https://doi.org/10.1016/j.aquabot.2006.03.010 |journal=Aquatic Botany |volume=85 |issue=3 |pages=241–243 |doi=10.1016/j.aquabot.2006.03.010 |issn=0304-3770|url-access=subscription }}