Tree

==Evolutionary history==
[[File:PSM V18 D630 Restoration of a lepidodendron.jpg|thumb|upright|''[[Lepidodendron]]'', an extinct [[Lycopodiophyta|lycophyte]] tree]]
[[File:PSM V16 D476 Principal palms and cycadeae of middle tertiary europe.jpg|thumb|upright|Palms and cycads as they might have appeared in the middle [[Tertiary era|Tertiary]]]]
{{further | Evolutionary history of plants}}

The earliest trees were [[tree fern]]s, [[horsetail]]s and [[lycophytes]], which grew in forests in the [[Carboniferous]] period. The first tree may have been ''[[Wattieza]]'', fossils of which have been found in [[New York (state)|New York state]] in 2007 dating back to the [[Middle Devonian]] (about 385 million years ago). Prior to this discovery, ''[[Archaeopteris]]'' was the earliest known tree.<ref>{{cite journal |doi=10.2307/2805124 |author=Beck, Charles B. |year=1960 |title=The identity of ''Archaeopteris'' and ''Callixylon'' |journal=Brittonia |volume=12 |issue=4 |pages=351–368 |jstor=2805124|bibcode=1960Britt..12..351B |s2cid=27887887 }}</ref> Both of these reproduced by spores rather than seeds and are considered to be links between ferns and the gymnosperms which evolved in the [[Triassic]] period. The gymnosperms include conifers, cycads, gnetales and [[ginkgo]]s and these may have appeared as a result of a [[Gene duplication#As an evolutionary event|whole genome duplication event]] which took place about 319 million years ago.<ref>{{cite journal |author=Jiao, Y. |author2=Wickett, N. J. |author3=Ayyampalayam, S. |author4=Chanderbali, A. S. |author5=Landherr, L. |author6=Ralph, P. E. |author7=Tomsho, L. P. |author8=Hu, Y. |author9=Liang, H. |author10-link=Soltis, P. S |author10=Soltis, P. S. |author11=Soltis, D. E. |author12=Clifton, S. W. |author13=Schlarbaum, S. E. |author14=Schuster, S. C. |author15=Ma, H. |author16=Leebens-Mack, J. |author17=dePamphilis, C. W. |display-authors=3 |year=2011 |title=Ancestral polyploidy in seed plants and angiosperms |journal=Nature |volume=473 |issue=7345 |pages=97–100 |doi=10.1038/nature09916 |pmid=21478875|bibcode=2011Natur.473...97J |s2cid=4313258 }}</ref> [[Ginkgophyta]] was once a widespread diverse group<ref>{{cite journal |author=Gnaedinger, Silvia |year=2012 |title=Ginkgoalean woods from the Jurassic of Argentina: Taxonomic considerations and palaeogeographical distribution |journal=Geobios |volume=45 |issue=2 |pages=187–198 |doi=10.1016/j.geobios.2011.01.007|bibcode=2012Geobi..45..187G |hdl=11336/25674 |hdl-access=free }}</ref> of which the only survivor is the maidenhair tree ''[[Ginkgo biloba]]''. This is considered to be a [[living fossil]] because it is virtually unchanged from the fossilised specimens found in Triassic deposits.<ref>{{cite web |url=http://www.ucmp.berkeley.edu/IB181/VPL/CorCon/CorCon2.html |title=''Ginkgo'' |author=Arens, Nan C. |year=1998 |work=Lab IX; Ginkgo, Cordaites and the Conifers |publisher=University of California Museum of Paleontology |access-date=25 July 2012 |archive-date=4 July 2017 |archive-url=https://web.archive.org/web/20170704102225/http://www.ucmp.berkeley.edu/IB181/VPL/CorCon/CorCon2.html |url-status=live }}</ref>

During the Mesozoic (245 to 66 million years ago) the conifers flourished and became adapted to live in all the major terrestrial habitats. Subsequently, the tree forms of [[flowering plant]]s evolved during the [[Cretaceous]] period. These began to [[dominance (ecology)|displace]] the conifers during the [[Tertiary]] era (66 to 2 million years ago) when forests covered the globe.<ref name=RFS/> When the climate cooled 1.5 million years ago and the first of four [[Glacial period|glacial periods]] occurred, the forests retreated as the ice advanced. In the [[interglacial]]s, trees recolonised the land that had been covered by ice, only to be driven back again in the next glacial period.<ref name=RFS>{{cite web |url=http://www.rfs.org.uk/learning/forestry-knowledge-hub/trees-biology/tree-evolution/ |title=Tree evolution |year=2012 |work=Tree Biology |publisher=Royal Forestry Society |access-date=25 July 2012 |archive-date=23 October 2016 |archive-url=https://web.archive.org/web/20161023054737/http://www.rfs.org.uk/learning/forestry-knowledge-hub/trees-biology/tree-evolution/ |url-status=live }}</ref>