Cycad

{{Short description|Division of naked-seeded dioecious plants}} {{good article}} {{Use dmy dates|date=September 2020}} {{Automatic taxobox |name = Cycadales |fossil_range = {{fossil range|Early Permian|0|earliest=300|Early Permian–Holocene}} |display_parents = 4 |image = Cycas circinalis.jpg |image_caption = ''Cycas rumphii'' with old and new male strobili |grandparent_authority = Bessey 1907: 321.<ref name="Bessey 1907">{{cite journal |last=Bessey |first=C.E. |year=1907 |title=A synopsis of plant phyla |journal=Nebraska University Studies |volume=7 |pages=275–373 }}</ref> |parent_authority = 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 |synonyms = * Cycadofilicales Němejc 1950 * Dioales Doweld 2001 * Stangeriales Doweld 2001 * Zamiales Burnett 1835 }}

'''Cycads''' {{IPAc-en|'|s|aI|k|ae|d|z}}—constituting the division '''Cycadophyta'''—are seed plants with a stout, woody cylindrical trunk with a crown of large, hard, stiff, evergreen and usually pinnate (feather-shaped) 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 and have long lifespans. They superficially resemble palms or ferns, but are not closely related to either group. Cycads are gymnosperms. Cycads have specialized pollinators, usually a specific beetle, and more rarely a thrips or a moth.

Both male and female cycads bear strobili, somewhat like conifer cones, containing their pollen and seeds, respectively. Cycads fix nitrogen in association with cyanobacteria living in their roots. Some species are used as narcotics, while in Vanuatu the plant symbolizes peace and appears on the national flag. Cycads all over the world are in decline, with four species on the brink of extinction and seven species each with fewer than 100 plants left in the wild.

== Description ==

Cycads are seed plants with a stout, woody, and usually unbranched cylindrical trunk, and a 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 name="Dehgan 1983">{{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 palms or ferns, they are sometimes mistaken for them, but they are not closely related to either group. Cycads are gymnosperms (naked-seeded), meaning their 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 pollinators, usually a specific beetle, and more rarely a thrips or a moth.<ref name="Cai 2018">{{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}}</ref>

The leaves are pinnate (shaped like feathers), 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, or have margins so deeply cut as to appear compound. The Australian genus ''Bowenia'' and some Asian species like ''Cycas multipinnata'', ''C. micholitzii'' and ''C. debaoensis'', have bipinnate leaves, the leaflets each having subleaflets.<ref>{{cite book |editor1-last=Rutherford |editor1-first=Catherine |display-editors=etal |title=CITES and Cycads: A user's guide |publisher=Royal Botanic Gardens, Kew |place=London, England |url=https://www.kew.org/sites/default/files/2019-02/CITESCycadsPack.pdf.pdf}}</ref> The apex of the stem is protected by modified leaves called cataphylls.<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 |doi-access=free |pmid=30551676 }}</ref>

Cycads superficially resemble palms in foliage and plant structure, occur in similar climates, and are often mistaken for them. However, they are so distantly related that they are classified in different phyla. Their similarities are caused by convergent evolution. Differences between cycads and palms include the cones (strobili) of cycads: they are gymnosperms, whereas palms are flowering plants and bear fruit. Both groups' mature foliage look similar, but young emerging cycad leaves – before they unfold and shift into place in the rosette crown – resemble a fiddlehead fern; in contrast, new leaves of palms are just miniature versions of a mature frond. Another difference is in the stem: Both phyla show scarring on their stems – below the rosette, where leaves used to attach – but the scars on a cycad's trunks are helically arranged and small; the scars on palm trunks are a circle, that wraps around the whole stem. The stems of cycads are generally rougher and shorter than those of palms.<ref name="Tudge 2006">{{cite book |last=Tudge |first=Colin |year=2006 |title=The Tree |location=New York |publisher=Crown Publishers |isbn=978-1-4000-5036-9 |pages=[https://archive.org/details/treenaturalhisto00tudg/page/70 70–72, 139–148] |url-access=registration |url=https://archive.org/details/treenaturalhisto00tudg |via=Internet Archive (archive.org)}}</ref>

<gallery class=center mode=nolines widths=200 heights=200> File:Cycads, Limpopo, South Africa (2417726335).jpg|Growth habit File: Cycad leaves semicircle.jpg|Rosette of pinnate leaves around a cylindrical trunk File:Cycad cone.jpg|Leaves and strobilus of ''Encephalartos sclavoi'' File:Bowenia spectabilis.JPG|''Bowenia spectabilis'': plant with single leaf </gallery>

== Evolution ==

=== Fossil record ===

[[File:Cycadeoidea marylandica - National Museum of Natural History - IMG 1978 (cropped).JPG|upright|thumb|Petrified fossil of ''Cycadeoidea marylandica'']]

The oldest probable cycad foliage is known from the latest Carboniferous to early Permian (around 300 million years ago) of South Korea and China, such as ''Crossozamia''. Unambiguous fossils are known from the early to middle Permian onwards.<ref name="Spiekermann 2021">{{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 |volume=289 |article-number=104415 |doi=10.1016/j.revpalbo.2021.104415 |bibcode=2021RPaPa.28904415S |s2cid=233860955 }}</ref> Cycads were uncommon during the Permian.<ref name="Gomankov 2022">{{cite journal |last=Gomankov |first=A.V. |date=June 2022 |title=Cycads in the Permian of thе Subangara region |journal=Paleontological Journal |volume=56 |issue=3 |pages=317–326 |doi=10.1134/S0031030122030066 |bibcode=2022PalJ...56..317G |s2cid=249627815 }}</ref> The two living cycad families diverged from each other at some time between the Carboniferous<ref name="Coiro Allio 2023">{{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 |pmid=37302411 |doi=10.1111/nph.19010 |doi-access=free |pmc=10953041 |bibcode=2023NewPh.240.1616C }}</ref> and the Jurassic.<ref name=Nagalingum2011/> Cycads are thought to have reached their apex of diversity during the Mesozoic.<ref name="Coiro 2024">{{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 |volume=7 |issue=1 |page=328 |doi=10.1038/s42003-024-06024-9 |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 Nilssoniales, were considerably more abundant than cycads during the Mesozoic: the "true" cycads were only 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 |volume=17 |issue=1 |page=97 |doi=10.1186/s12862-017-0943-x |doi-access=free |pmc=5383990 |pmid=28388891 |bibcode=2017BMCEE..17...97C }}</ref> The oldest records of the modern genus ''Cycas'' are from the Paleogene of east Asia.<ref name="Liu Lindstrom 2022">{{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 |volume=129 |issue=2 |pages=217–230 |doi=10.1093/aob/mcab118 |doi-access=free |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 from the Cenozoic.<ref name=Condamine-2015/>

=== Phylogeny ===

The two extant families of cycads both belong to the order Cycadales, and are the Cycadaceae and Zamiaceae (including Stangeriaceae). These cycads may have changed little since the Jurassic in comparison to some other plant divisions, but are by no means "living fossils" as they have continued to evolve.<ref name="Nagalingum2011"/> Based on genetic studies, cycads are thought to be more closely related to ''Ginkgo'' than to other living gymnosperms. They 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 |pmc=3595029 |pmid=23315384}}</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 |display-authors=5 |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 |url=https://www.nature.com/articles/s41477-021-00964-4 |url-access=subscription }}</ref>

==== External phylogeny ====

The Cycads have traditionally been thought to fall within the seed plants as the sister lineage to other groups. However, a more modern view is that they are Gymnosperms.<ref name="Wu 2013"/><ref name="Stull 2021"/>

{| |- |style="vertical-align:top|

{|style="border:0; margin:auto;" |- |style="padding:10px;"|{{clade |label1=Seed plants |1={{clade |1='''Cycads''' 70px |2=''Ginkgo'' 50px |3={{clade |1=Conifers 50px |label2=Anthophytes |2={{clade |1=† Bennettitales 70px |2= Gnetales 70px |3= Angiosperms 50px }} }} }} }}

|style="padding:10px;"|{{clade |label1=Seed plants |1={{clade |label1=Gymnosperms |1={{clade |1='''Cycads''' 70px |2=''Ginkgo'' 50px |3={{clade |1=Conifers 50px |2=Gnetophytes 70px }} }} |2=Angiosperms 50px }} }} |- ! {{small|Traditional view}} ! {{small|Modern view}} |} |}

==== Internal phylogeny ====

The Cycads are in two clades, the Cycadaceae and the Zamiaceae.<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 |doi-access=free |pmc=4449600 |bibcode=2015BMCEE..15...65C }}</ref>

{{clade|label1=Cycads |1={{clade |label1=Cycadineae |1={{clade |label1=Cycadaceae |1=''Cycas'' 70px }} |label2=Zamiineae |2={{clade |label1=Zamiaceae |1={{clade |label1=Diooideae |1=''Dioon'' 70px |label2=Zamioideae |2={{clade |label1=Encephalarteae |1={{clade |1=''Macrozamia'' 70px |2={{clade |1=''Lepidozamia'' 50px |2=''Encephalartos'' 50px }} }} |label2=Zamieae |2={{clade |1=''Bowenia'' 70px |2={{clade |1={{clade |1=''Ceratozamia'' 70px |2=''Stangeria'' 50px }} |2={{clade |1=''Zamia'' 70px |2=''Microcycas'' 50px }} }} }} }} }} }} }} }}

=== Taxonomy ===

Classification of extant Cycadophyta to genus:<ref>{{cite web |title=''Cycadophyta'' Bessey |url=https://www.worldfloraonline.org/taxon/wfo-4100003333 |website=World Flora Online |access-date=20 August 2025 |id=wfo-4100003333}}</ref>

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

== Distribution and ecology ==

thumb|upright=2|Global distribution of cycad genera. Red areas: cycad diversity; Purple dots: sampled fossil localities<ref name="Coiro Allio Mazet 2023"/>

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">{{cite book |editor1-last=Orchard |editor1-first=A.E. |editor2-last=McCarthy |editor2-first=P.M. |year=1998 |title=Flora of Australia |volume=48 |pages=1–766 |publisher=Australian Government Publishing Service |place=Canberra, Australia }}</ref> The greatest diversity is in the Americas, but they also grow in China, South and Southeast Asia, the Pacific islands, and southern and tropical Africa.<ref>{{cite web |title=Global Distribution of Cycadales |url=https://www.researchgate.net/figure/Global-distribution-of-Cycadales-a-Species-richness-of-the-10-extant-cycad-genera_fig1_371489209 |website=ResearchGate |access-date=20 August 2025}}</ref><ref name="Coiro Allio Mazet 2023">{{cite journal |last1=Coiro |first1=Mario |last2=Allio |first2=Rémi |last3=Mazet |first3=Nathan |last4=Seyfullah |first4=Leyla J. |last5=Condamine |first5=Fabien L. |title=Reconciling fossils with phylogenies reveals the origin and macroevolutionary processes explaining the global cycad biodiversity |journal=New Phytologist |volume=240 |issue=4 |date=2023 |pmid=37302411 |pmc=10953041 |doi=10.1111/nph.19010 |doi-access=free |pages=1616–1635 |bibcode=2023NewPh.240.1616C }}</ref> Some are xerophytes that can survive in desert or semi-desert climates,<ref name="Northern Territory">{{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 name="Bermingham Dick 2005">{{cite book |last1=Bermingham |first1=E. |last2=Dick |first2=C.W. |last3=Moritz |first3=C. |year=2005 |title=Tropical Rainforests: Past, present, and future |publisher=University of Chicago Press |isbn=978-0-226-04468-2 |url=https://books.google.com/books?id=Y3dXZyCCDpEC}}</ref> and some in both.<ref name="Redlist">{{cite report |title=The IUCN Red List of Threatened Species |chapter=''Macrozamia communis'' |type=annual list |publisher=International Union for Conservation of Nature |place=Gland, CH |chapter-url=http://iucnredlist.org/details/42000/0}}</ref>

Cycads accommodate nitrogen-fixing cyanobacteria in their coralloid roots.<ref name="Rai Soderback 2000">{{cite journal |author1=Rai, A.N. |author2=Soderback, E. |author3=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> The cyanobacteria produce a neurotoxin, BMAA, that accumulates in the plants' seeds, possibly as a defense against herbivores.<ref name=Holtcamp>{{cite journal |last=Holtcamp |first=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 |article-number=20152397 |pmid=26791617 |pmc=4795023}}</ref>

Cycads have acquired a family of genes (fitD) from a microbe, most likely a fungus, via horizontal gene transfer, 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 |display-authors=5 |journal=Nature Plants |volume=8 |issue=4 |pages=389–401 |pmid=35437001 |pmc=9023351 |bibcode=2022NatPl...8..389L }}</ref>

== Relationship with humans ==

Nuts of ''Cycas orientis'' (''nyathu'') are eaten by the Yolngu in Australia's Arnhem Land. They are harvested during the dry season and soaked in water overnight before being ground into a paste, wrapped under bark, and cooked on an open fire.<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> A pair of ''namele'' cycad leaves, representing peace, appears on the Flag of Vanuatu.<ref>{{cite web |last=Oslievskyi |first=Yevhenii |title=Human Relationships with Cycads: Cycads in Vanuatu: Tabu mo Kot |url=https://ethnobiology.org/conference/sessions/42/human-relationships-cycads |access-date=20 August 2025 |quote=The leaves of cycads ('namele' in Bislama) appear as one of the most prominent objects in the symbolic vocabulary of Vanuatu archipelago since the time the first ethnographic accounts on the territory were written. They continue to occupy a privileged place in the country's culture today: namele leaves are portrayed on Vanuatu's flag, used in the practice of traditional courts, and chiefly authorities.}}</ref><ref name="VIMB">{{cite web |title=The Vanuatu Flag: An Emblem of Unity, Tradition, and Prosperity |url=https://vimb.vu/the-vanuatu-flag-an-emblem-of-unity-tradition-and-prosperity/ |publisher=VIMB |access-date=20 August 2025 |date=19 May 2023}}</ref> Cycads are used as narcotics in Mexico, where they are among the substances called "peyote", while in South Africa, ''Encephalartos'' is used for the same purpose. In both regions, collecting for the drugs market is harming wild cycad populations.<ref>{{cite web |last=Bonta |first=Mark|title=Cycads: Cycads in as Narcotics |url=https://ethnobiology.org/conference/sessions/42/human-relationships-cycads |access-date=20 August 2025 |quote=Cycads are ingested for narcotic purposes and are likely hallucinogens. The Nahuatl term 'peyote' ...}}</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 name="Davis 2018">{{cite news |last=Davis |first=Judi |date=27 June 2018 |title=Meet Durban's famous cycad family |work=South Coast Herald |url=https://southcoastherald.co.za/297604/meet-durbans-famous-cycad-family/}}</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=11 February 2025}}</ref><ref name="BSSA">{{cite news |title=Cycad Project |work=Botanical Society of South Africa |url=https://botanicalsociety.org.za/cycad-project/}}</ref> The Fossil Cycad National Monument was a protected area in South Dakota from 1922, containing many fossils of ''Cycadeoidea''.<ref>{{cite web |title=Fossil Cycad National Monument |url=https://www.nps.gov/articles/fossil-cycad-national-monument.htm |access-date=13 December 2021 |publisher=National Park Service}}</ref> After vandalism of the exposed fossils, the status was withdrawn in 1957.<ref name="Hughes">{{cite web |first1=Vincent L. |last1=Santucci |first2=Marikka |last2=Hughes |title=Fossil Cycad National Monument: A Case of Paleontological Resource Mismanagement |url=https://www.nps.gov/parkhistory/online_books/northern_plains/cycad_mismanagement.pdf |access-date=29 August 2018}}</ref>

''Cycas micronesica'' seeds, containing β-Methylamino-L-alanine, were made into flour by the Chamorro people of Guam as a dietary staple. Chronic dietary exposure to BMAA is now considered to be a cause of the amyotrophic lateral sclerosis/parkinsonism–dementia complex (ALS/PDC) that had an extremely high rate of incidence among the Chamorro.<ref name=Cox2>{{cite journal |vauthors=Cox PA, Sacks OW | s2cid = 12044484 | year = 2002 | title = Cycad neurotoxins, consumption of flying foxes, and ALS-PDC disease in Guam | journal = Neurology | volume = 58 | pages = 956–9 | doi=10.1212/wnl.58.6.956 | pmid=11914415 | issue=6}}</ref> The Chamorro call the condition ''lytico-bodig''.<ref name=Kurland /> In the 1950s, ALS/PDC prevalence ratios and death rates for Chamorro residents of Guam and Rota were 50–100 times that of developed countries, including the United States.<ref name=Kurland>{{cite journal | author = Kurland, LK |author2=Mulder, DW | year = 1954 | title = Epidemiologic investigations of amyotrophic lateral sclerosis | journal = Neurology | volume = 4|issue=5 |doi=10.1212/wnl.4.5.355 |pmid=13185376 | pages=355–78|s2cid=44801930 }}</ref> No demonstrable heritable or viral factors were found for the disease, and a subsequent decline of ALS/PDC after 1963 on Guam led to the search for responsible environmental agents.<ref name=Galasko>{{cite journal |vauthors=Galasko D, Salmon DP, Craig UK, Thal LJ, Schellenberg G, Wiederholt W | year = 2002 | title = Clinical features and changing patterns of neurodegenerative disorders on Guam, 1997-2000 | journal = Neurology | volume = 58 | issue = 1 | pages = 90–7 | doi=10.1212/wnl.58.1.90| pmid = 11781411 | s2cid = 24248686 }}</ref>(<ref name=Hill>{{cite journal | author = Hill, K.D. | year = 1994 | title = The cycas rumphii complex (Cycadeceae) in New Guinea and the Western Pacific | journal = Australian Systematic Botany | volume = 7 | issue = 6 | pages = 543–567 | doi=10.1071/sb9940543 | bibcode = 1994AuSyB...7..543H }}</ref>) <ref name=Whiting>{{cite journal | author = Whiting, M.G. | year = 1963 | title = Toxicity of cycads | journal = Economic Botany | volume = 17 | issue = 4 | pages = 270–302 | doi=10.1007/bf02860136| bibcode = 1963EcBot..17..270W | s2cid = 31799259 }}</ref> Cycads harbor symbiotic cyanobacteria of the genus ''Nostoc'' in specialized roots which push up through the leaf litter into the light; these cyanobacteria produce BMAA.<ref>{{citation |author1=Rai, A.N. |author2=Soderback, E. |author3=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> In addition to eating traditional food items from cycad flour directly, BMAA may be ingested by humans through biomagnification. Flying foxes, a Chamorro delicacy, forage on the fleshy seed covering of cycad seeds and concentrate the toxin in their bodies. Twenty-four specimens of flying foxes from museum collections were tested for BMAA, which was found in large concentrations in the flying foxes from Guam.<ref name=Banack2>{{cite journal |vauthors=Banack SA, Murch SJ, Cox PA | year = 2006 | title = Neurotoxic flying foxes as dietary items for the Chamorro people, Mariana Islands | journal = Ethnopharmacology | volume = 106 | issue = 1 | pages = 97–104 | doi = 10.1016/j.jep.2005.12.032| pmid = 16457975 }}</ref> As of 2021 studies continued examining BMAA biomagnification in marine and estuarine systems and its possible impact on human health outside of Guam.<ref>{{cite journal | last1=Wang | first1=Chao | last2=Yan | first2=Chen | last3=Qiu | first3=Jiangbing | last4=Liu | first4=Chao | last5=Yan | first5=Yeju | last6=Ji | first6=Ying | last7=Wang | first7=Guixiang | last8=Chen | first8=Hongju | last9=Li | first9=Yang | last10=Li | first10=Aifeng | title=Food web biomagnification of the neurotoxin β-N-methylamino-L-alanine in a diatom-dominated marine ecosystem in China | journal=Journal of Hazardous Materials | volume=404 | year=2021 | issue=Pt B | issn=0304-3894 | doi=10.1016/j.jhazmat.2020.124217|doi-access=free | article-number=124217| pmid=33129020 | bibcode=2021JHzM..40424217W }}</ref>

== References ==

== Further reading ==

{{ubli | {{Cite book |first=David L. |last=Jones |date=2002 |title=Cycads of the World |edition=2nd |publisher=Smithsonian Books |author-link=David L. Jones (botanist) |isbn=978-1-5883-4043-6 }} | {{Cite book |first1=Loran M. |last1=Whitelock |first2=Duke |last2=Benadom |date=2015 |title=The Cycads |type=2nd ed., 2 volumes |publisher=Superb Succulents |author1-link=Loran Whitelock |isbn=978-0-9896-5142-4 |oclc=935926513}} }}

== External links ==

* [http://www.pacsoa.org.au/ Palm and Cycad Societies of Australia] * [http://cycadsociety.org/ Cycad Society of South Africa]

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

Cycads Category:Dioecious plants Category:Cisuralian first appearances Category:Extant Permian first appearances