Editing Xylem (section)

== Primary and secondary xylem ==
'''Primary xylem''' is formed during primary growth from [[procambium]]. It includes protoxylem and metaxylem. Metaxylem develops after the protoxylem but before secondary xylem. Metaxylem has wider vessels and tracheids than protoxylem.{{cn|date=January 2025}}

'''Secondary xylem''' is formed during secondary growth from [[vascular cambium]]. Although secondary xylem is also found in members of the [[gymnosperm]] groups [[Gnetophyta]] and [[Ginkgophyta]] and to a lesser extent in members of the [[Cycadophyta]], the two main groups in which secondary xylem can be found are:
# [[conifers]] (''Coniferae''): there are approximately 600 known species of conifers.<ref name="Judd">{{cite book|last=Walter S. Judd|title=Plant systematics: A phylogenetic approach|date=2002|publisher=W.H. Freeman |isbn=0-87893-403-0|editor-last=Walter S. Judd|edition=2|url-access=registration|url=https://archive.org/details/plantsystematics0002unse}}</ref> All species have secondary xylem, which is relatively uniform in structure throughout this group. Many conifers become tall trees: the secondary xylem of such trees is used and marketed as [[softwood]].
# [[angiosperms]] (''Angiospermae''): there are approximately 250,000<ref name=Judd/> known species of angiosperms. Within this group secondary xylem is rare in the [[monocots]].<ref>{{cite book|author=Dickison, W.C.|year=2000|title=Integrative Plant Anatomy (page 196)|publisher=Elsevier Science|isbn=9780080508917|url=https://books.google.com/books?id=-os1kvkFbS0C|url-status=live|archive-url=https://web.archive.org/web/20171106151303/https://books.google.com/books?id=-os1kvkFbS0C|archive-date=2017-11-06}}</ref> Many non-monocot angiosperms become trees, and the secondary xylem of these is used and marketed as [[hardwood]].