Cycas

Cycas is a genus of cycad, and the only genus in the family Cycadaceae. About 113 species are accepted, which are native to the Indo-Pacific, East Africa and Madagascar.[3] Cycas circinalis, a species endemic to India, was the first cycad species to be described in western literature, and is the type species of the genus. The best-known Cycas species is Cycas revoluta.

Cycas
Temporal range:
A large cycas under development
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Gymnosperms
Division: Cycadophyta
Class: Cycadopsida
Order: Cycadales
Suborder: Cycadineae
Family: Cycadaceae
Pers.[1]
Genus: Cycas
L.[2]
Type species
C. circinalis[2]
L.[2]
Synonyms[3]
  • Dyerocycas Nakai
  • Epicycas de Laub.
  • Todda-pana Adans.

Range
See also: List of cycad species by country

The genus is native to the Old World, with the species concentrated around the equatorial regions - eastern and southeastern Asia including the Philippines with 10 species (9 of which are endemic), eastern Africa (including Madagascar), northern Australia, Polynesia, and Micronesia. Australia has 26 species, while the Indo-Chinese area has about 30. India has 9 species. The northernmost species (C. revoluta) is found at 31°N in southern Japan. The southernmost (C. megacarpa) is found at 26°S in southeast Queensland. Due to the occurrence of large number of Cycas species in China, Australia and India, those countries are considered as centres of Cycas diversity.[4]

Evolution
Cycas sp.

Cycas is thought to have a deep split from all other living cycads, with estimates of the timing of the split ranging from the Jurassic[5] to the Carboniferous.[6] Fossil seeds from the Middle Jurassic of England and British Columbia were suggested in a 2017 study to be more closely related to Cycas than other cycads, and were assigned to the same family, Cycadaceae.[7] However, a later study suggested that these seeds could not be assigned to the stem-group of Cycas with confidence due to lacking the double vascular system that characterises the seeds of all living cycads.[8] The leaf fossil genus Paracycas known from the Jurassic and Cretaceous of Europe has been suggested to be early representatives of the Cycas lineage by cladistic analysis.[6] The earliest fossils assignable to Cycas are known from the Paleogene of East Asia, such as Cycas fushunensis from the Eocene of Northeast China, with East Asia likely representing the ancestral homeland of the genus.[9]

Morphology
Bark of Cycas rumphii

The plants are dioecious, and the family Cycadaceae is unique among the cycads in not forming seed cones on female plants, but rather a group of leaf-like structures called megasporophylls each with seeds on the lower margins, and pollen cones or strobilus on male individuals.

The caudex is cylindrical, surrounded by the persistent petiole bases. Most species form distinct branched or unbranched trunks but in some species the main trunk can be subterranean with the leaf crown appearing to arise directly from the ground. There are two types of leaves - foliage leaves and scaly leaves. The foliage leaves are pinnate (or more rarely bipinnate) and arranged spirally, with thick and hard keratinose. They are not permanent and fall off leaving back leaf-bases. The leaflets are articulated, have midrib but lack secondary veins. The scaly leaves are persistent, brown in colour and protective in function. Megasporophylls are not gathered in cones. Pollination takes place by air.

Reproduction
A male cone of Cycas circinalis
A male cone of Cycas orixensis with unique forked microsporophylls

Cykas take about 10 years to reach sexual maturity, after years of exclusive vegetative growth, which occurs by bulbils arising at the base of the trunk.

Conservation status

Cycas species are threatened worldwide and almost all the species are listed in the IUCN Red List. Cycas beddomei is the only species of the genus Cycas listed in Appendix I of CITES. All other members of Cycadaceae are listed under Appendix II.[10] Cycas rumphii and Cycas pectinata have the most widespread distribution.

Phylogeny
Cycas media megasporophylls with nearly-mature seeds on a wild plant in north Queensland, Australia
Grove of Cycas media in north Queensland
Cycas platyphylla in north Queensland with new flush of fronds during the rainy season, still with glaucous bloom
Phylogeny of Cycas[11][12]
section

C. micholitzii Dyer

Stangerioides
(Pectinata)

C. multipinnata Chen & Yang

C. pectinata Buchanan-Hamilton

C. thouarsii Brown ex Gaudichaud-Beaupré

(Panzhihuaenses)
section

C. revoluta Thunberg (Sago palm)

C. taitungensis Shen et al.

Asiorientales
section

C. tropophylla Hill & Lôc

C. ferruginea Wei

C. curranii (Schuster) Hill

C. debaoensis Zhong & Chen

C. brachycantha Hill, Nguyên & Lôc

C. immersa Craib

Panzhihuaenses
(Cycas)

C. bifida (Dyer) Hill

C. szechuanensis Cheng & Fu

section
subsection

C. wadei Merrill

Wadeanae
subsection

C. hainanensis Chen

C. taiwaniana Carruthers

C. fairylakea Wang

Taiwanianosae
Wadeanae
section
subsection

C. circinalis L. (Indu)

C. micronesica Hill

Cycas
subsection

C. pschannae Srivastava & Singh

C. edentata de Laubenfels

C. nitida Hill & Lindström

C. rumphii Miquel

Rumphiae
Cycas
section

C. clivicola Hill

subsection

C. siamensis Miquel

C. vespertilio Lindström & Hill

C. riuminiana Porte ex Regel

C. bougainvilleana Hill

C. celebica Miquel

Indosinenses
subsection

C. macrocarpa Griffith

C. nongnoochiae Hill

C. elongata (Leandri) Wang

C. tansachana Hill & Yang

C. lindstromii Yang, Hill & Nguyên

C. condaoensis Hill & Yang

C. chamaoensis Hill

C. media Brown

Lindstroemiae
Indosinenses
section

C. diannanensis Guan & Tao

C. cairnsiana von Mueller

C. petrae Lindström & Hill

C. megacarpa Hill

C. calcicola Maconochie

C. armstrongii Miquel

C. balansae Warburg

C. segmentifida Wang & Deng

C. dolichophylla Hill, Nguyên & Lôc

C. simplicipinna (Smitinand) Hill

C. guizhouensis Lan & Zou

C. chevalieri Leandri

C. maconochiei Chirgwin & Hill

C. arenicola Hill

C. schumanniana Lauterbach

C. aculeata Hill & Nguyên

C. silvestris Hill

C. basaltica Gardner

C. semota Hill

C. orientis Hill

C. canalis Hill

C. hongheensis Yang & Yang ex Wang

C. conferta Chirgwin

C. angulata Brown

C. couttsiana Hill

C. ophiolitica Hill

C. tanqingii Wang

C. platyphylla Hill

C. indica Lindström & Hill (=Cycas swamyi)

C. annaikalensis Rita Singh &Radha

C. beddomei Dyer

C. sphaerica Roxburgh

Endemicae

Other species:

References
  1. Kramer, K.U.; Green, P.S., eds. (1990). Pteridophytes and Gymnosperms (PDF). The families and genera of vascular plants. Vol. 1. Assisted by E. Götz (illustrations). Berlin: Springer-Verlag. p. 370. ISBN 978-3-540-51794-8.
  2. Hill, Ken; Leonie Stanberg; Dennis Stevenson. "The Cycad Pages". Genus Cycas. Royal Botanic Gardens Sydney. Archived from the original on 2021-03-01. Retrieved 6 September 2013.
  3. "Cycas L." Plants of the World Online. Royal Botanic Gardens, Kew. Retrieved 28 March 2023.
  4. "World Checklist of Selected Plant Families (WCSP)". World Checklist of Selected Plant Families. Board of Trustees of the Royal Botanic Gardens, Kew. Archived from the original on 13 April 2020. Retrieved 28 March 2023.
  5. Nagalingum, N. S.; Marshall, C. R.; Quental, T. B.; Rai, H. S.; Little, D. P.; Mathews, S. (2011-11-11). "Recent Synchronous Radiation of a Living Fossil". Science. 334 (6057): 796–799. Bibcode:2011Sci...334..796N. doi:10.1126/science.1209926. ISSN 0036-8075. PMID 22021670. S2CID 206535984.
  6. Coiro, Mario; Allio, Rémi; Mazet, Nathan; Seyfullah, Leyla J.; Condamine, Fabien L. (2023-06-11). "Reconciling fossils with phylogenies reveals the origin and macroevolutionary processes explaining the global cycad biodiversity". New Phytologist. doi:10.1111/nph.19010. ISSN 0028-646X. PMID 37302411. S2CID 259137975.
  7. Spencer, Alan R. T.; Garwood, Russell J.; Rees, Andrew R.; Raine, Robert J.; Rothwell, Gar W.; Hollingworth, Neville T. J.; Hilton, Jason (2017-08-28). "New insights into Mesozoic cycad evolution: an exploration of anatomically preserved Cycadaceae seeds from the Jurassic Oxford Clay biota". PeerJ. 5: e3723. doi:10.7717/peerj.3723. ISSN 2167-8359. PMC 5578371. PMID 28875075.
  8. Rothwell, Gar W.; Stockey, Ruth A.; Stevenson, Dennis W.; Zumajo-Cardona, Cecilia (2022-10-01). "Large Permineralized Seeds in the Jurassic of Haida Gwaii, Western Canada: Exploring the Mode and Tempo of Cycad Evolution". International Journal of Plant Sciences. 183 (8): 674–690. doi:10.1086/721710. ISSN 1058-5893. S2CID 251947260.
  9. Liu, Jian; Lindstrom, Anders J; Marler, Thomas E; Gong, Xun (2022-01-28). "Not that young: combining plastid phylogenomic, plate tectonic and fossil evidence indicates a Palaeogene diversification of Cycadaceae". Annals of Botany. 129 (2): 217–230. doi:10.1093/aob/mcab118. ISSN 0305-7364. PMC 8796677. PMID 34520529.
  10. "Appendices I, II and III". Convention on International Trade in Endangered Species of Wild Fauna and Flora. 21 May 2023. Retrieved 22 August 2023.
  11. Stull, Gregory W.; Qu, Xiao-Jian; Parins-Fukuchi, Caroline; Yang, Ying-Ying; Yang, Jun-Bo; Yang, Zhi-Yun; Hu, Yi; Ma, Hong; Soltis, Pamela S.; Soltis, Douglas E.; Li, De-Zhu; Smith, Stephen A.; Yi, Ting-Shuang; et al. (2021). "Gene duplications and phylogenomic conflict underlie major pulses of phenotypic evolution in gymnosperms". Nature Plants. 7 (8): 1015–1025. bioRxiv 10.1101/2021.03.13.435279. doi:10.1038/s41477-021-00964-4. PMID 34282286. S2CID 232282918.
  12. Stull, Gregory W.; et al. (2021). "main.dated.supermatrix.tree.T9.tre". Figshare. doi:10.6084/m9.figshare.14547354.v1. {{cite journal}}: Cite journal requires |journal= (help)
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