View source for Cycad

{{Short description|Division of naked seeded dioecious plants}}
{{For|the insect|Cicada}}
{{Use dmy dates|date=September 2020}}
{{Automatic taxobox
| name = Cycadales
| fossil_range = {{fossil range|Early Permian|0|earliest=300|[[Early Permian]]&ndash;[[Holocene]]}}
| display_parents = 4
| image = Cycas circinalis.jpg
| image_caption = ''[[Cycas rumphii]]'' with old and new male strobili.
| grandparent_authority = [[Charles Edwin Bessey|Bessey]] 1907: 321.<ref name="Bessey 1907">{{cite journal | last=Bessey | first=C.E. | year=1907 | title=A synopsis of plant phyla | journal=Nebraska Univ. Stud. | volume=7 | pages=275–373 }}</ref>
| parent_authority = [[Adolphe-Théodore Brongniart|Brongn.]]<ref name="Brongniart 1843">{{cite book | last=Brongniart | first=A. | year=1843 | title=Énumération des genres de plantes cultivées au Muséum d'histoire naturelle de Paris }}</ref>
| taxon = Cycadales
| authority = Pers. ex Bercht. & J. Presl
| subdivision_ranks = Extant groupings
| subdivision = *[[Cycadaceae]]
*[[Zamiaceae]]
| range_map = 
| range_map_caption = Global distribution of modern cycads
| synonyms = * Cycadofilicales <small>Němejc 1950</small>
* Dioales <small>Doweld 2001</small>
* Stangeriales <small>Doweld 2001</small>
* Zamiales <small>Burnett 1835</small>
}}

[[File:Cycads, Limpopo, South Africa (2417726335).jpg|thumb|Cycads in South Africa]]

'''Cycads''' {{IPAc-en|'|s|aI|k|ae|d|z}} are [[seed plant]]s that typically have a stout and woody ([[ligneous]]) [[trunk (botany)|trunk]] with a [[crown (botany)|crown]] of large, hard, stiff, [[evergreen]] and (usually) [[pinnate]] leaves. The species are [[dioecious]], that is, individual plants of a species are either male or female. Cycads vary in size from having trunks only a few centimeters to several meters tall. They typically grow slowly<ref>{{Cite journal |last=Dehgan |first=Bijan |year=1983 |title=Propagation and Growth of Cycads—A Conservation Strategy |url=https://journals.flvc.org/fshs/article/view/95611 |journal=Proceedings of the Florida State Horticultural Society |volume=96 |pages=137–139|via=Florida Online Journals}}</ref> and have long lifespans. Because of their superficial resemblance to [[Arecaceae|palms]] or [[fern]]s, they are sometimes mistaken for them, but they are not closely related to either group.
Cycads are [[gymnosperms]] (naked-seeded), meaning their [[fertilization|unfertilized]] seeds are open to the air to be directly fertilized by [[pollination]], as contrasted with [[angiosperms]], which have enclosed seeds with more complex fertilization arrangements. Cycads have very specialized [[pollinator]]s, usually a specific [[beetle]], and more rarely a [[thrips]] or a [[moth]].<ref>{{Cite journal |last1=Cai |first1=Chenyang |last2=Escalona |first2=Hermes E. |last3=Li |first3=Liqin |last4=Yin |first4=Ziwei |last5=Huang |first5=Diying |last6=Engel |first6=Michael S. |date=2018-09-10 |title=Beetle Pollination of Cycads in the Mesozoic |url=https://www.sciencedirect.com/science/article/pii/S0960982218308273#:~:text=Cycads%20are%20dioecious%20gymnosperms,%20and,(Thysanoptera)%20%5B3%5D. |journal=Current Biology |volume=28 |issue=17 |pages=2806–2812.e1 |doi=10.1016/j.cub.2018.06.036 |pmid=30122529 |bibcode=2018CBio...28E2806C |issn=0960-9822}}</ref>

Both male and female cycads bear cones ([[strobilus|strobili]]), somewhat similar to [[conifer cone]]s.

Cycads have been reported to [[nitrogen fixation|fix nitrogen]] in association with various [[cyanobacteria]] living in the roots (the "coralloid" roots).<ref>{{cite journal |vauthors=Rai AN, Soderback E, Bergman B |year=2000 |title=Tansley Review No. 116. Cyanobacterium-Plant Symbioses |journal=The New Phytologist |volume=147 |issue=3 |pages=449–481 |jstor=2588831 |doi=10.1046/j.1469-8137.2000.00720.x |pmid=33862930 |doi-access=free }}</ref> These photosynthetic bacteria produce a [[neurotoxin]] called [[BMAA]] that is found in the [[seed]]s of cycads. This neurotoxin may enter a  human food chain as the cycad seeds may be eaten directly as a source of flour by humans or by wild or feral animals such as bats, and humans may eat these animals. It is hypothesized that this is a source of some [[neurological disease]]s in humans.<ref name=Holtcamp>{{cite journal | author = Holtcamp, W. | year = 2012 | title = The emerging science of BMAA: do cyanobacteria contribute to neurodegenerative disease? | journal = Environmental Health Perspectives | volume = 120 | issue = 3 | doi = 10.1289/ehp.120-a110 | pmid=22382274 | pmc=3295368 | pages=a110–a116}}</ref><ref name="Cox and Davis">{{cite journal | vauthors = Cox PA, Davis DA, Mash DC, Metcalf JS, Banack SA | year = 2015 | title = Dietary exposure to an environmental toxin triggers neurofibrillary tangles and amyloid deposits in the brain | journal = Proceedings of the Royal Society B | volume = 283 | issue = 1823 | doi = 10.1098/rspb.2015.2397 | pages=20152397 | pmid=26791617 | pmc=4795023}}</ref> Another defence mechanism against herbivores is the accumulation of toxins in seeds and vegetative tissues; through [[horizontal gene transfer]], cycads have acquired a family of genes ([[Pseudomonas_protegens#Insecticidal_activity|fitD]]) from a microbial organism, most likely a fungus, which gives them the ability to produce an insecticidal toxin.<ref>{{cite journal | doi=10.1038/s41477-022-01129-7 |doi-access=free | title=The Cycas genome and the early evolution of seed plants | year=2022 | last1=Liu | first1=Yang | last2=Wang | first2=Sibo | last3=Li | first3=Linzhou | last4=Yang | first4=Ting | last5=Dong | first5=Shanshan | last6=Wei | first6=Tong | last7=Wu | first7=Shengdan | last8=Liu | first8=Yongbo | last9=Gong | first9=Yiqing | last10=Feng | first10=Xiuyan | last11=Ma | first11=Jianchao | last12=Chang | first12=Guanxiao | last13=Huang | first13=Jinling | last14=Yang | first14=Yong | last15=Wang | first15=Hongli | last16=Liu | first16=Min | last17=Xu | first17=Yan | last18=Liang | first18=Hongping | last19=Yu | first19=Jin | last20=Cai | first20=Yuqing | last21=Zhang | first21=Zhaowu | last22=Fan | first22=Yannan | last23=Mu | first23=Weixue | last24=Sahu | first24=Sunil Kumar | last25=Liu | first25=Shuchun | last26=Lang | first26=Xiaoan | last27=Yang | first27=Leilei | last28=Li | first28=Na | last29=Habib | first29=Sadaf | last30=Yang | first30=Yongqiong | journal=Nature Plants | volume=8 | issue=4 | pages=389–401 | pmid=35437001 | pmc=9023351 |bibcode=2022NatPl...8..389L | display-authors=1 }}</ref>

Cycads all over the world are in decline, with four species on the brink of extinction and seven species having fewer than 100 plants left in the wild.<ref>{{Cite news |last=Davis |first=Judi |date=2018-06-27 |title=Meet Durban's famous cycad family |work=South Coast Herald |url=https://southcoastherald.co.za/297604/meet-durbans-famous-cycad-family/ |access-date=2022-09-11}}</ref><ref>{{Cite news |title=Protecting cycads through microdots |work=Botanical Society of South Africa |url= https://botanicalsociety.org.za/cycad-micro-dotting/ |access-date=2025-02-11}}</ref><ref>{{Cite news |title=Cycad Project |work=Botanical Society of South Africa |url= https://botanicalsociety.org.za/cycad-project/ |access-date=2025-02-11}}</ref>

== Description ==
[[File: Cycad leaves semicircle.jpg|thumb|Cycads have a rosette of pinnate leaves around a cylindrical trunk]]
Cycads have a [[cylindrical]] trunk which usually does not [[branch]]. However, some types of cycads, such as ''[[Cycas zeylanica]],'' can branch their trunks. The apex of the stem is protected by modified leaves called [[cataphyll]]s.<ref>{{cite journal | pmc=6315973 | year=2018 | last1=Marler | first1=T. E. | last2=Krishnapillai | first2=M. V. | title=Does Plant Size Influence Leaf Elements in an Arborescent Cycad? | journal=Biology | volume=7 | issue=4 | page=51 | doi=10.3390/biology7040051 | pmid=30551676 | doi-access=free }}</ref> Leaves grow directly from the trunk, and typically fall when older, leaving a crown of leaves at the top. The leaves grow in a [[rosette (botany)|rosette]], with new foliage emerging from the top and center of the crown. The trunk may be buried, so the leaves appear to be emerging from the ground, so the plant appears to be a basal rosette. The leaves are generally large in proportion to the trunk size, and sometimes even larger than the trunk.

The leaves are [[pinnate]] (in the form of bird feathers, [[pinnation|pinnae]]), with a central leaf stalk from which parallel "ribs" emerge from each side of the stalk, perpendicular to it. The leaves are typically either compound (with [[leaflet (botany)|leaflets]] emerging from the leaf stalk as "ribs"), or have edges ([[Leaf margin|margin]]s) so deeply cut ([[Wiktionary:incised|incised]]) so as to appear compound. The Australian genus ''[[Bowenia]]'' and some Asian species of Cycas, like ''[[Cycas multipinnata]]'', ''[[Cycas micholitzii|C.&nbsp;micholitzii]]'' and ''[[Cycas debaoensis|C.&nbsp;debaoensis]]'', have leaves that are [[bipinnate]], the leaflets each having their own subleaflets, growing [[Self-similar|in the same form]] on the leaflet as the leaflets do on the stalk.<ref>{{Cite book |last=Rutherford |first=Catherine |url=https://www.kew.org/sites/default/files/2019-02/CITESCycadsPack.pdf.pdf |title=CITES and Cycads: A User's Guide |publisher=Royal Botanic Gardens, Kew |display-editors=et al.}}</ref><ref>{{cite book | url=https://books.google.com/books?id=_EMbBAAAQBAJ&dq=C.+multipinnata+within+the+genus.+C.+debaoensis&pg=PA129 | title=Cycadaceae Family | isbn=9781300654537 | last1=Lariushin | first1=Boris | date=19 January 2013 | publisher=Lulu.com }}</ref>

== Confusion with palms ==
Due to superficial similarities in foliage and plant structure, cycads and [[Arecaceae|palms]] are often mistaken for each other. They also can occur in similar climates. However, they belong to different [[Phylum|phyla]] and as such are not closely related. The similar structure is the product of [[convergent evolution]].

Beyond those superficial resemblances, there are a number of differences between cycads and palms. For one, cycads are [[gymnosperm]]s and bear cones (strobili), while palms are [[angiosperm]]s and so flower and bear fruit. The mature foliage looks similar between both groups, but the young emerging leaves of a cycad resemble a [[fiddlehead fern]] before they unfold and take their place in the rosette, while the leaves of palms are just small versions of the mature frond. Another difference is in the [[Plant stem|stem]]. Both plants leave some scars on the stem below the rosette where there used to be leaves, but the scars of a cycad are [[Helical symmetry|helically]] arranged and small, while the scars of palms are a circle that wraps around the whole stem. The stems of cycads are also in general rougher and shorter than those of palms.<ref>{{Cite book |title=The Tree |last=Tudge |first=Colin |publisher=Crown Publishers |year=2006 |isbn=978-1-4000-5036-9 |location=New York |pages=[https://archive.org/details/treenaturalhisto00tudg/page/70 70–72, 139–148] |url-access=registration |url=https://archive.org/details/treenaturalhisto00tudg}}</ref>

==Taxonomy==
{{More citations needed|date=November 2018}}
The two extant [[family (biology)|families]] of cycads both belong to the order [[Cycadales]], and are the [[Cycadaceae]] and [[Zamiaceae]] (including [[Stangeriaceae]]). These cycads have changed little since the Jurassic in comparison to some other plant divisions. Five additional families belonging to the [[Medullosales]] became extinct by the end of the Paleozoic Era.

Based on genetic studies, cycads are thought to be more closely related to ''[[Ginkgo]]'' than to other living gymnosperms. Both are thought to have diverged from each other during the early [[Carboniferous]].<ref name="Wu 2013">{{cite journal |last1=Wu |first1=Chung-Shien |last2=Chaw |first2=Shu-Miaw |last3=Huang |first3=Ya-Yi |date=January 2013 |title=Chloroplast phylogenomics indicates that ''Ginkgo biloba'' is sister to cycads |journal=Genome Biology and Evolution |volume=5 |issue=1 |pages=243–254 |doi=10.1093/gbe/evt001 |issn=1759-6653 |pmc=3595029 |pmid=23315384 |language=en}}</ref><ref name="Stull 2021">{{cite journal |last1=Stull  |first1=Gregory W. |last2=Qu |first2=Xiao-Jian |last3=Parins-Fukuchi |first3=Caroline |last4=Yang |first4=Ying-Ying |last5=Yang |first5=Jun-Bo |last6=Yang |first6=Zhi-Yun |last7=Hu |first7=Yi |last8=Ma |first8=Hong |last9=Soltis |first9=Pamela S. |last10=Soltis |first10=Douglas E. |last11=Li |first11=De-Zhu |date=July 19, 2021 |title=Gene duplications and phylogenomic conflict underlie major pulses of phenotypic evolution in gymnosperms |journal=Nature Plants |volume=7 |issue=8 |pages=1015–1025 |doi=10.1038/s41477-021-00964-4 |pmid=34282286 |bibcode=2021NatPl...7.1015S |s2cid=236141481 |issn=2055-0278 |language=en |url=https://www.nature.com/articles/s41477-021-00964-4|url-access=subscription }}</ref>

{| class="wikitable"
|-
! colspan=1 | External phylogeny<ref name="Wu 2013"/><ref name="Stull 2021"/>
|- 
| style="vertical-align:top|

{| style="border:0; margin:auto;"
|-
|style="padding:10px;"|{{clade
|1={{clade
  |1='''Cycads'''
  |2=''[[Ginkgo]]''
  |3={{clade
    |1=[[Conifers]]
    |label2=Anthophytes
    |2={{clade
      |1=[[Bennettitales]]
      |2=[[Gnetales]]
      |3=[[Angiosperms]]
       }}
     }}
   }}
}}
|style="padding:10px;"|{{clade 
|1={{clade
  |label1=[[Gymnosperm]]s
  |1={{clade 
    |1='''Cycads'''
    |2=''[[Ginkgo]]'' 
    |3={{clade 
      |1=[[Conifers]]
      |2=[[Gnetophytes]]
       }}
     }}
  |label2=[[Angiosperm]]s
  |2=(flowering plants)
   }}
}}
|-
!<br/>{{small|Traditional view}}
!<br/>{{small|Modern view}}
|}
|}

{| class="wikitable"
|-
! colspan=1 | Internal phylogeny<ref name="Nagalingum2011">{{cite journal |last1=Nagalingum |first1=N. S. |last2=Marshall |first2=C. R. |last3=Quental |first3=T. B. |last4=Rai |first4=H. S. |last5=Little |first5=D. P. |last6=Mathews |first6=S. |date=2011 |title=Recent synchronous radiation of a living fossil |journal=Science |volume=334 |issue=6057 |pages=796–799 |bibcode=2011Sci...334..796N |doi=10.1126/science.1209926 |pmid=22021670 |s2cid=206535984}}</ref><ref name="Condamine-2015">{{cite journal |last1=Condamine |first1=Fabien L. |last2=Nagalingum |first2=Nathalie S. |last3=Marshall |first3=Charles R. |last4=Morlon |first4=Hélène |date=17 April 2015 |title=Origin and diversification of living cycads: a cautionary tale on the impact of the branching process prior in Bayesian molecular dating |journal=BMC Evolutionary Biology |volume=15 |issue=1 |at=65 |doi=10.1186/s12862-015-0347-8 |pmid=25884423|s2cid=14815027 |language=en |doi-access=free|pmc=4449600 |bibcode=2015BMCEE..15...65C }}</ref>
|- 
| style="vertical-align:top|

{| style="border:0; margin:auto;"
|-
|style="padding:10px;"|{{clade|style=font-size:90%;line-height:80%;width:300px
|label1 =Cycads
|1={{clade
  |label1=Cycadineae
  |1={{clade
    |label1=[[Cycadaceae]]
    |1=''[[Cycas]]''
     }}
  |label2=Zamiineae
  |2={{clade
    |label1=[[Zamiaceae]]
    |1={{clade
      |label1=Diooideae
      |1=''[[Dioon]]''
      |label2=Zamioideae
      |2={{clade
        |label1=Encephalarteae
        |1={{clade
          |1=''[[Macrozamia]]''
          |2={{clade
            |1=''[[Lepidozamia]]''
            |2=''[[Encephalartos]]''
             }}
           }}
        |label2=Zamieae
        |2={{clade
          |1=''[[Bowenia]]''
          |2={{clade
            |1={{clade
              |1=''[[Ceratozamia]]''
              |2=''[[Stangeria]]''
               }}
            |2={{clade
              |1=''[[Zamia]]''
              |2=''[[Microcycas]]''
               }}
             }}
           }}
         }}
       }}
     }}
   }}
}}
|}
|}

Classification of the Cycadophyta to the rank of family.

* Class Cycadopsida <small>Brongniart 1843</small>
** Order Cycadales <small>Persoon ex von Berchtold & Presl 1820</small>
*** Suborder Cycadineae <small>Stevenson 1992</small>
**** Family [[Cycadaceae]] <small>Persoon 1807</small>
***** Genus ''[[Cycas]]''
*** Suborder Zamiineae <small>Stevenson 1992</small>
**** Family [[Zamiaceae]] <small>Horaninow 1834</small>
***** subfamily Diooideae <small>Pilg. 1926</small>
****** Tribe Diooeae <small>Schuster</small>
******* Genus ''[[Dioon]]''
***** subfamily Zamioideae <small>Stevenson 1992</small>
****** Tribe Encephalarteae <small>Miquel 1861</small>
******* Genus ''[[Macrozamia]]''
******* Genus ''[[Lepidozamia]]''
******* Genus ''[[Encephalartos]]''
****** Tribe Zamieae <small>Miquel 1861</small>
******* Genus ''[[Bowenia]]''
******* Genus ''[[Ceratozamia]]''
******* Genus ''[[Stangeria]]''
******* Genus ''[[Zamia]]''
******* Genus ''[[Microcycas]]''

=== Fossil genera ===
The following extinct cycad genera are known:<ref>{{Cite web |title=PBDB |url=https://paleobiodb.org/classic/basicTaxonInfo?taxon_no=55349 |access-date=2024-03-16 |website=paleobiodb.org}}</ref>

* ''[[Amuriella]]'' Late Jurassic, Russian Far East (leaf fragments)
* ''[[Androstrobus]]'' Triassic to Cretaceous, worldwide (leaf form genus)
* ''[[Antarcticycas]]'' Middle Triassic, Antarctica (known from the whole plant)<ref>{{Cite journal |last1=Hermsen |first1=Elizabeth J. |last2=Taylor |first2=Edith L. |last3=Taylor |first3=Thomas N. |date=January 2009 |title=Morphology and ecology of the ''Antarcticycas'' plant |journal=Review of Palaeobotany and Palynology |language=en |volume=153 |issue=1–2 |pages=108–123 |doi=10.1016/j.revpalbo.2008.07.005|bibcode=2009RPaPa.153..108H }}</ref>
* ?''[[Anthrophyopsis]]'' Late Triassic, worldwide (leaf form genus, possibly a [[Pteridospermatophyta|pteridospermatophyte]])<ref>{{Cite journal |last1=Xu |first1=Yuanyuan |last2=Popa |first2=Mihai Emilian |last3=Zhang |first3=Tingshan |last4=Lu |first4=Ning |last5=Zeng |first5=Jianli |last6=Zhang |first6=Xiaoqing |last7=Li |first7=Liqin |last8=Wang |first8=Yongdong |date=2021-09-01 |title=Re-appraisal of Anthrophyopsis (Gymnospermae): New material from China and global fossil records |url=https://www.sciencedirect.com/science/article/pii/S0034666721000993 |journal=Review of Palaeobotany and Palynology |volume=292 |pages=104475 |doi=10.1016/j.revpalbo.2021.104475 |bibcode=2021RPaPa.29204475X |issn=0034-6667|url-access=subscription }}</ref>
* ''[[Apoldia]]'' Triassic-Jurassic, Europe
* ''[[Archaeocycas]]'' Early Permian, Texas (leaf with sporophylls)
* ''[[Aricycas]]'' Late Triassic, Arizona (leaf form genus)
* ''[[Beania (plant)|Beania]]'' (=''Sphaereda''), Triassic to Jurassic, Europe & Central Asia (leaf form genus)
* ''[[Behuninia]]'' Late Jurassic, Colorado & Utah (fruiting structures)
* ''[[Bucklandia]]'' Middle Jurassic to Early Cretaceous, Europe and India (leaf form genus)
* ''[[Bureja (genus)|Bureja]]'' Late Jurassic, Russia
* ''[[Cavamonocolpites]]'' Early Cretaceous, Brazil (pollen)
* ''[[Crossozamia]]'' Early to Late Permian, China (leaf form genus)
* ''[[Ctenis]]'' Mesozoic-Paleogene, Worldwide (leaf form genus)
* ''[[Ctenozamites]]'' Triassic-Cretaceous, worldwide (leaf form genus)
* ''[[Cycadenia]]'' Triassic, Pennsylvania (trunks)
* ''[[Cycadinorachis]]'' Late Jurassic, India (rachis)
* ''[[Fascisvarioxylon]]'' Late Jurassic, India (petrified wood)
* ''[[Gymnovulites]]'', Latest Cretaceous/earliest Paleocene, India (seed)
* ''[[Heilungia]]'', Late Jurassic to early Cretaceous, Russia & Alaska (leaf form genus)
* ''[[Leptocycas]]'' Late Triassic, North Carolina & China (known from the whole plant)<ref>{{Cite journal |last1=Zhang |first1=Jian-Wei |last2=Yao |first2=Jian-Xin |last3=Chen |first3=Jia-Rui |last4=Li |first4=Cheng-Sen |date=2010-05-25 |title=A new species of Leptocycas (Zamiaceae) from the Upper Triassic sediments of Liaoning Province, China |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1759-6831.2010.00079.x |journal=Journal of Systematics and Evolution |language=en |volume=48 |issue=4 |pages=286–301 |doi=10.1111/j.1759-6831.2010.00079.x|bibcode=2010JSyEv..48..286Z }}</ref>
* ''[[Mesosingeria]]'', Jurassic to Early Cretaceous, Antarctica & Argentina (leaf form genus)
* ''[[Michelilloa]]'', Late Triassic, Argentina (stem)
* ?''[[Nikania]]'', Early Cretaceous, Russia (leaf fragments)
* ?''[[Nilssonia (plant)|Nilssonia]]'', Middle Permian to Late Cretaceous, worldwide (leaf form genus) (possibly not a cycad)<ref>{{Cite journal |last1=Vajda |first1=Vivi |last2=Pucetaite |first2=Milda |last3=McLoughlin |first3=Stephen |last4=Engdahl |first4=Anders |last5=Heimdal |first5=Jimmy |last6=Uvdal |first6=Per |date=August 2017 |title=Molecular signatures of fossil leaves provide unexpected new evidence for extinct plant relationships |url=https://www.nature.com/articles/s41559-017-0224-5 |journal=Nature Ecology & Evolution |language=en |volume=1 |issue=8 |pages=1093–1099 |bibcode=2017NatEE...1.1093V |doi=10.1038/s41559-017-0224-5 |issn=2397-334X |pmid=29046567 |s2cid=3604369}}</ref>
* ?''[[Nilssoniocladus]]'', Early to Late Cretaceous, United States & Russia (stems, likely associated with ''Nilssonia'', possibly [[deciduous]])<ref>{{Cite journal |last1=Spicer |first1=Robert A. |last2=Herman |first2=Alexey B. |date=1996-05-01 |title=Nilssoniocladus in the Cretaceous Arctic: new species and biological insights |url=https://dx.doi.org/10.1016/0034-6667%2895%2900111-5 |journal=Review of Palaeobotany and Palynology |volume=92 |issue=3 |pages=229–243 |doi=10.1016/0034-6667(95)00111-5 |bibcode=1996RPaPa..92..229S |issn=0034-6667|url-access=subscription }}</ref>
* ''[[Palaeozamia]]'', Middle Jurassic, England
* ''[[Paracycas]]'', Middle Jurassic to Late Jurassic, Europe and Central Asia
* ?''[[Phasmatocycas]]'', Late Carboniferous to Early Permian, Kansas, Texas & New Mexico (leaf with sporophylls)<ref>{{Cite journal |last1=Axsmith |first1=Brian J. |last2=Serbet |first2=Rudolph |last3=Krings |first3=Michael |last4=Taylor |first4=Thomas N. |last5=Taylor |first5=Edith L. |last6=Mamay |first6=Sergius H. |date=2003 |title=The Enigmatic Paleozoic plants Spermopteris and Phasmatocycas reconsidered |url=https://bsapubs.onlinelibrary.wiley.com/doi/10.3732/ajb.90.11.1585 |journal=American Journal of Botany |language=en |volume=90 |issue=11 |pages=1585–1595 |doi=10.3732/ajb.90.11.1585 |pmid=21653333 |bibcode=2003AmJB...90.1585A |issn=0002-9122|url-access=subscription }}</ref>
* ''[[Pleiotrichium]]'', Late Cretaceous, Germany (leaf)
* ''[[Pseudoctenis]]'', Late Permian to Late Cretaceous, worldwide (leaf form genus)
* ''[[Sarmatiella]]'', Late Triassic, Ukraine 
* ''[[Stangerites]]'', Late Triassic to Early Jurassic, Virginia and Mexico (leaf form genus)
* ''[[Sueria]]'', Early Cretaceous, Argentina (leaf)
* ''[[Taeniopteris]]'', Carboniferous to Cretaceous, worldwide (polyphyletic leaf form genus, also includes bennettitales and [[Marattiales|marattialean]] ferns)

==Fossil record==

[[File:Bowenia spectabilis.JPG|thumb|''[[Bowenia spectabilis]]'' : plant with single frond in the Daintree rainforest, north-east Queensland]]

[[File:Cycad cone.jpg|upright|thumb|Leaves and strobilus of ''[[Encephalartos sclavoi]]'']]

The oldest probable cycad foliage is known from the latest Carboniferous-Early Permian of South Korea and China, such as ''[[Crossozamia]]''. Unambiguous fossils of cycads are known from the Early-Middle Permian onwards.<ref>{{Cite journal |last1=Spiekermann |first1=Rafael |last2=Jasper |first2=André |last3=Siegloch |first3=Anelise Marta |last4=Guerra-Sommer |first4=Margot |last5=Uhl |first5=Dieter |date=June 2021 |title=Not a lycopsid but a cycad-like plant: ''Iratinia australis'' gen. nov. et sp. nov. from the Irati Formation, Kungurian of the Paraná Basin, Brazil |journal=Review of Palaeobotany and Palynology |language=en |volume=289 |pages=104415 |doi=10.1016/j.revpalbo.2021.104415 |bibcode=2021RPaPa.28904415S |s2cid=233860955}}</ref> Cycads were generally uncommon during the Permian.<ref>{{Cite journal |last=Gomankov |first=A. V. |date=June 2022 |title=Cycads in the Permian of thе Subangara Region  |journal=Paleontological Journal |language=en |volume=56 |issue=3 |pages=317–326 |doi=10.1134/S0031030122030066 |bibcode=2022PalJ...56..317G |s2cid=249627815 |issn=0031-0301}}</ref> The two living cycad families are thought to have split from each other sometime between the Jurassic<ref name="Nagalingum2011" /> and Carboniferous.<ref name=":0">{{Cite journal |last1=Coiro |first1=Mario |last2=Allio |first2=Rémi |last3=Mazet |first3=Nathan |last4=Seyfullah |first4=Leyla J. |last5=Condamine |first5=Fabien L. |date=2023-06-11 |title=Reconciling fossils with phylogenies reveals the origin and macroevolutionary processes explaining the global cycad biodiversity |journal=New Phytologist |volume=240 |issue=4 |pages=1616–1635 |language=en |doi=10.1111/nph.19010 |pmid=37302411 |issn=0028-646X|doi-access=free |pmc=10953041 |bibcode=2023NewPh.240.1616C }}</ref> Cycads are thought to have reached their apex of diversity during the Mesozoic.<ref>{{Cite journal |last1=Coiro |first1=Mario |last2=Seyfullah |first2=Leyla Jean |date=2024-03-14 |title=Disparity of cycad leaves dispels the living fossil metaphor |journal=Communications Biology |language=en |volume=7 |issue=1 |page=328 |doi=10.1038/s42003-024-06024-9 |issn=2399-3642 |pmc=10940627 |pmid=38485767}}</ref> Although the Mesozoic is sometimes called the "Age of Cycads,"  some other groups of distantly related extinct seed plants with similar foliage, such as [[Bennettitales]] and [[Nilssonia (plant)|Nilssoniales]] were considerably more abundant than cycads during the Mesozoic, with true cycads being minor components of Mesozoic vegetation.<ref name="Coiro-2017">{{Cite journal |last1=Coiro |first1=Mario |last2=Pott |first2=Christian |date=December 2017 |title=Eobowenia gen. nov. from the Early Cretaceous of Patagonia: indication for an early divergence of Bowenia? |journal=BMC Evolutionary Biology |language=en |volume=17 |issue=1 |pages=97 |doi=10.1186/s12862-017-0943-x |issn=1471-2148 |pmc=5383990 |pmid=28388891 |doi-access=free |bibcode=2017BMCEE..17...97C }}</ref> The oldest records of the modern genus ''Cycas'' are from the Paleogene of East Asia.<ref>{{Cite journal |last1=Liu |first1=Jian |last2=Lindstrom |first2=Anders J |last3=Marler |first3=Thomas E |last4=Gong |first4=Xun |date=2022-01-28 |title=Not that young: combining plastid phylogenomic, plate tectonic and fossil evidence indicates a Palaeogene diversification of Cycadaceae |journal=Annals of Botany |language=en |volume=129 |issue=2 |pages=217–230 |doi=10.1093/aob/mcab118 |doi-access=free |issn=0305-7364 |pmc=8796677 |pmid=34520529}}</ref> Fossils assignable to Zamiaceae are known from the Cretaceous,<ref name="Coiro-2017" /> with fossils assignable to living genera of the family known from the Cenozoic.<ref name="Condamine-2015" />

[[File:Fossilized cycad New York Botanical Garden.jpg|upright|thumb|Petrified cycad fossil, New York Botanical Garden]]

==Distribution==

{{See also|List of cycad species by country}}

The living cycads are found across much of the [[subtropical]] and [[tropical]] parts of the world, with a few in temperate regions such as in Australia.<ref name="Orchard1998">Orchard, A.E. & McCarthy, P.M. (eds.) (1998). Flora of Australia 48: 1–766. Australian Government Publishing Service, Canberra.</ref> The greatest diversity occurs in [[South America|South]] and [[Central America]].{{citation needed|date=July 2015}} They are also found in [[Mexico]], the [[Antilles]], southeastern [[United States of America|United States]], [[Australia]], [[Melanesia]], [[Micronesia]], [[Japan]], [[China]], [[Southeast Asia]], [[Bangladesh]], [[India]], [[Sri Lanka]], [[Madagascar]], and [[Southern Africa|southern]] and tropical [[Africa]], where at least 65 [[species]] occur. Some can survive in harsh [[desert]] or semi-desert [[climate]]s ([[xerophytic]]),<ref>{{cite report |title=National Recovery Plan for the MacDonnell Ranges Cycad ''Macrozamia macdonnellii'' |publisher=Department of Natural Resources, Environment, The Arts and Sport, Northern Territory |url=http://www.environment.gov.au/system/files/resources/c17de516-c635-4c67-b040-c9db4da380e4/files/macrozamia-macdonnellii.pdf |access-date=16 July 2015}}</ref> others in wet [[rain forest]] conditions,<ref>{{cite book |author1=Bermingham, E. |author2=Dick, C.W. |author3=Moritz, C. |year=2005 |title=Tropical Rainforests: Past, Present, and Future |publisher=University of Chicago Press |isbn=9780226044682 |url=https://books.google.com/books?id=Y3dXZyCCDpEC}}</ref> and some in both.<ref>{{citation |chapter-url=http://iucnredlist.org/details/42000/0 |title=The IUCN Red List of Threatened Species |chapter=''Macrozamia communis''}}</ref> Some can grow in [[sand]] or even on [[rock (geology)|rock]], some in oxygen-poor, swampy, [[bog]]-like soils rich in [[organic material]].{{Citation needed|date=April 2011}} Some are able to grow in full sun, some in full shade, and some in both.{{Citation needed|date=April 2011}} Some are [[Sodium chloride|salt]] tolerant ([[halophyte]]s).{{citation needed|date=July 2015}}

Species diversity of the extant cycads peaks at 17˚ 15"N and 28˚ 12"S, with a minor peak at the [[equator]]. There is therefore not a [[Latitudinal gradients in species diversity|latitudinal diversity gradient]] towards the equator but towards the [[Tropic of Cancer]] and the [[Tropic of Capricorn]]. However, the peak near the northern tropic is largely due to ''Cycas'' in Asia and ''Zamia'' in the New World, whereas the peak near the southern tropic is due to ''Cycas'' again, and also to the diverse genus ''Encephalartos'' in southern and central Africa, and ''Macrozamia'' in Australia. Thus, the distribution pattern of cycad species with latitude appears to be an artifact of the geographical isolation of the remaining cycad genera and their species, and perhaps because they are partly [[xerophytic]] rather than simply [[tropical]].{{citation needed|date=February 2025}}

==Cultural significance==
Nuts of the ''[[Cycas orientis]]'' (''nyathu'') are coveted by the [[Yolngu]] in Australia's [[Arnhem Land]] as a source of food. They are harvested on their [[Indigenous Australian seasons#North coast – Yolngu seasons|dry season]] to leach its poison under water overnight before ground into a paste, wrapped under bark and cooked on open fire until done.<ref>{{cite book|page=48|isbn=978-1-921953-31-6|publisher=National Museum of Australia Press|title= Midawarr {{!}} Harvest: The Art of Mulkun Wirrpanda and John Wolseley |url=https://www.nma.gov.au/about/publications/midawarr-harvest|year=2017}}</ref> Roots of ''[[Zamia integrifolia]]'' were used by the [[Seminole]] and other native peoples to produce [[Florida arrowroot]] by a similar process.

In [[Vanuatu]], the cycad is known as ''namele'' and is an important symbol of traditional culture. It serves as a powerful [[taboo]] sign,<ref>{{cite web |author=Dan McGarry |date=Apr 9, 2018 |title=A Princely Title |website=Vanuatu Daily Post |url=http://dailypost.vu/news/a-princely-title/article_3b08dcb8-6286-51f6-bc85-ac5aee546242.html}}</ref> and a pair of ''namele'' leaves appears on the [[Flag of Vanuatu|national flag]] and coat of arms. Together with the [[Cordyline terminalis|nanggaria]] plant, another symbol of Vanuatu culture, the ''namele'' also gives its name to [[Nagriamel]], an indigenous political movement.

==See also==

* [[Fossil Cycad National Monument]], now withdrawn, in the U.S. state of South Dakota{{-}}

==References==
{{Reflist|25em}}

==External links==
{{Commons}}
* {{cite web |url=http://palm-trees.org/ |title=Palm Trees, Small Palms, Cycads, Bromeliads and tropical plants |archive-url=https://web.archive.org/web/20140520003137/http://palm-trees.org/ |archive-date=2014-05-20}} Site with thousands of large, high quality photos of cycads and associated flora. Includes information on habitat and cultivation. (Site is dead.)
* {{cite web |title=The Cycad Pages |publisher=Royal Botanic Gardens Sydney |url= http://plantnet.rbgsyd.nsw.gov.au/PlantNet/cycad/index.html |url-status=dead |archive-date=29 March 2021 |archive-url=https://web.archive.org/web/20210329132148/https://plantnet.rbgsyd.nsw.gov.au/PlantNet/cycad/index.html}}
* {{cite web |url=http://www.conifers.org/zz/cycadales.htm |title=Gymnosperm Database: Cycads |archive-url=https://web.archive.org/web/20100810215325/http://www.conifers.org/zz/cycadales.htm |archive-date=2010-08-10}}
* {{cite web |title=Fairchild Tropical Botanic Garden |url=http://www.fairchildgarden.org/horticulture/n_collections.html |archive-url=https://web.archive.org/web/20150223092247/http://www.fairchildgarden.org/horticulture/n_collections.html |archive-date=2015-02-23}} One of the largest collections of cycads in the world in Florida, U.S.A.
* {{cite web |title=Main Page |url=http://www.pacsoa.org.au/ |publisher=Palm and Cycad Societies of Australia (PACSOA) |access-date=2023-06-18}}
* {{cite web |title=Welcome |url=http://cycadsociety.org/ |publisher=The Cycad Society of South Africa |access-date=2023-06-18}}
* {{cite web |author=David Dalton |date=1997 |title=Part I. The range of organisms that can fix nitrogen |website=Nitrogen Fixation |url=http://academic.reed.edu/biology/Nitrogen/Nfix1.html |access-date=2023-06-18}} Cycad nitrogen fixation
* {{cite web |title=Cycad toxicity |website=The Cycad Pages |publisher=Royal Botanic Gardens Sydney |url=http://plantnet.rbgsyd.nsw.gov.au/PlantNet/cycad/toxic.html |url-status=dead |archive-date=2020-07-17 |archive-url=https://web.archive.org/web/20200717151457/http://plantnet.rbgsyd.nsw.gov.au/PlantNet/cycad/toxic.html}} 
* {{cite web |author=Lauren Kessler |date=Aug 28, 2005 |url=https://www.nytimes.com/2005/08/28/magazine/the-cult-of-the-cycads.html |url-status=live |archive-url=https://web.archive.org/web/20220604003638/https://www.nytimes.com/2005/08/28/magazine/the-cult-of-the-cycads.html |archive-date=2022-06-04 |title=The Cult of the Cycads |work=[[The New York Times Magazine]]}} Magazine article on cycad collectorship and cycad smuggling.

{{Plant classification}}
{{Nuts}}
{{Life on Earth}}

{{Taxonbar|from1=Q1089795|from2=Q157114|from3=Q5197912|from4=Q5605610}}
{{Authority control}}

[[Category:Cycads| ]]
[[Category:Dioecious plants]]
[[Category:Cisuralian first appearances]]
[[Category:Extant Permian first appearances]]