Editing Cycad (section)

{{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|thrip]] 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>