# Hardwood
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{{Short description|Wood from angiosperm trees}}
{{Other uses|Hardwood (disambiguation)}}
{{Distinguish|Heartwood}}
{{pp-vandalism|small=yes}}
{{More citations needed|date=November 2014}}
[[File:Fagus wood.jpg|250px|right|thumb|[Beech](/source/Beech) is a popular hardwood]]
'''Hardwood''' is [wood](/source/wood) from [flowering](/source/flowering_plant) (angiosperm) [tree](/source/tree)s. These are usually found in [broad-leaved](/source/broad-leaved_tree) [temperate](/source/temperate_forest) and [tropical forest](/source/tropical_forest)s.[{{cite book |title=Forests And Forest Plants – Volume II |first1=John N.|last1=Owens |first2=H. Gyde|last2=Lund |edition= |publisher=EOLSS Publications |year=2009 |isbn=978-1-905839-39-1 |page=[https://books.google.com/books?id=9dqpCwAAQBAJ&pg=PA134 134] |url=https://books.google.com/books?id=9dqpCwAAQBAJ |via=[Google Books](/source/Google_Books)}}] In [temperate](/source/temperate_climate) and [boreal](/source/boreal_ecosystem) [latitude](/source/latitude)s, they are mostly [deciduous](/source/deciduous), but in the [tropics](/source/tropical_climate) and [subtropics](/source/subtropics), they are mostly [evergreen](/source/evergreen). Hardwood (which comes from [angiosperm](/source/angiosperm) trees) contrasts with [softwood](/source/softwood) (which is from [gymnosperm](/source/gymnosperm) trees).
==Characteristics==
[[Image:Hard Soft Wood.jpg|250px|thumb|[SEM](/source/Scanning_electron_microscope) images showing the presence of pores in hardwoods ([oak](/source/oak), top) and absence in [softwood](/source/softwood)s ([pine](/source/pine), bottom)]]
Hardwoods are produced by [angiosperm](/source/Flowering_plant) trees that reproduce by flowers, and have broad leaves. Many species are deciduous.[{{cite web |url=https://www.treehugger.com/identification-of-the-most-common-hardwoods-1341843 |title=Identification of the Most Common Hardwoods |last=Nix |first=Steve |website=Treehugger|date=December 20, 2022|orig-date=Originally published April 22, 2021 |access-date=June 4, 2024}}] Those of temperate regions lose their leaves every autumn as temperatures fall and are dormant in the winter, but those of tropical regions may shed their leaves in response to seasonal or sporadic periods of drought. Hardwood from deciduous species, such as oak, normally shows annual [growth rings](/source/dendrochronology), but these may be absent in some [tropical hardwoods](/source/tropical_timber).[{{cite web |last1=MinuteEarth |title=Why Hardwoods Are The Softest Woods |url=https://www.youtube.com/watch?v=saR_rSHY9kA |archive-url=https://ghostarchive.org/varchive/youtube/20211221/saR_rSHY9kA |archive-date=2021-12-21 |url-status=live|website=YouTube |date=October 9, 2020}}{{cbignore}}]
Hardwoods have a more complex structure than softwoods and are often much slower growing as a result. The dominant feature separating "hardwoods" from softwoods is the presence of pores, or [vessels](/source/vessel_element).[CRC Handbook of Materials Science, Vol IV, pg 15] The vessels may show considerable variation in size, shape of perforation plates (simple, scalariform, reticulate, foraminate), and structure of cell wall, such as spiral thickenings. Several specific microscopic features are used in the identification process of a hardwood species.[{{cite web | title= Hardwood Identification Criteria| url=http://mantanis.users.uth.gr/Hardwood-anatomy.pdf | access-date=2024-12-16}} Presentation by Dr. George I. Mantanis (Univ. of Thessaly, 2024)]
As the name suggests, the wood from these trees is generally harder than that of softwoods, but there are significant exceptions. In both groups there is an enormous variation in actual wood hardness, with the range in density in hardwoods completely including that of softwoods; some hardwoods (''e.g.'', [balsa](/source/Ochroma_pyramidale)) are softer than most softwoods, while [yew](/source/taxus) is an example of a hard softwood.
==Chemistry==
The structural polymers of hardwoods are [cellulose](/source/cellulose), [hemicellulose](/source/hemicellulose), and [lignin](/source/lignin).[{{cite book |last1=Ansell |first1=Martin P. |title=Woodhead Publishing Series in Composites Science and Engineering: Number 54. Wood Composites |date=2015 |publisher=Woodhead Publishing |location=Cambridge, UK |isbn=978-1-78242-454-3 |chapter=Chapter 11: Preservation, Protection and Modification of Wood Composites}}] The constituents of hardwood lignin differs from those included in softwood. [Sinapyl alcohol](/source/Sinapyl_alcohol) and [coniferyl alcohol](/source/coniferyl_alcohol) are the main monomers of hardwood lignin.[{{cite journal |last1=Boerjan |first1=Wout |last2=Ralph |first2=John |last3=Baucher |first3=Marie |title=Ligninbiosynthesis |journal=Annual Review of Plant Biology |date=June 2003 |volume=54 |issue=1 |pages=519–546 |doi=10.1146/annurev.arplant.54.031902.134938|pmid=14503002 |bibcode=2003AnRPB..54..519B |url=https://biblio.ugent.be/publication/211742/file/4144786 |url-access=subscription }}]
Hardwoods contain a smaller quantity of non-structural constituents, named [extractives](/source/Wood), than softwoods.[{{cite book |last1=Ek |first1=Monica |last2=Gellerstedt |first2=Göran |last3=Henriksson |first3=Gunnar |title=Pulp and Paper Chemistry and Technology. Volume 1, Wood Chemistry and Wood Biotechnology |date=2009 |publisher=Walter de Gruyter |location=Berlin |isbn=978-3-11-021339-3 |chapter=Chapter 7: Wood extractives}}] These extractives are usually categorized into three broad groups: [aliphatic compound](/source/aliphatic_compound)s, [terpene](/source/terpene)s and [phenolic compound](/source/Phenols)s. Aliphatic compounds found in hardwoods include [fatty acid](/source/fatty_acid)s, [fatty alcohol](/source/fatty_alcohol)s and their [ester](/source/ester)s with [glycerol](/source/glycerol), fatty alcohols (waxes) and sterols (steryl esters), [hydrocarbon](/source/hydrocarbon)s, such as [alkane](/source/alkane)s, [sterol](/source/sterol)s, such as [sitosterol](/source/sitosterol), [sitostanol](/source/sitostanol) and [campesterol](/source/campesterol).[{{cite book |last1=Sjöström |first1=Eero |title=Wood Chemistry: Fundamentals and Applications |location=San Diego |isbn=978-0-08-092589-9 |edition=Second |chapter=Chapter 5: Extractives |publisher=Elsevier Science |date=October 22, 2013 }}] The terpene content of the hardwood significantly differs from the softwood, and mainly consists of [triterpenoid](/source/triterpenoid)s, [polyprenol](/source/polyprenol)s and other higher terpenes. Triterpenoids commonly purified from hardwoods include [cycloartenol](/source/cycloartenol), [betulin](/source/betulin) and [squalene](/source/squalene). Hardwood polyterpenes are [rubber](/source/rubber), [gutta percha](/source/gutta_percha), gutta-balatá and betulaprenols.