Cycas

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

Cycas is a genus of cycad. It is the only genus in the family Cycadaceae. About 113 species are accepted, which are native to the Asia-Pacific, East Africa and Madagascar.[4] 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.

Range[edit]

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.[3]

Evolution[edit]

Cycas sp.

Cycas is though to have split from all other living cycads at least 200 million years ago, possibly much earlier. 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, were assigned to the same family, Cycadaceae.[5] 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.[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.[7]

Morphology[edit]

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[edit]

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

The plant takes several years to grow, sexual reproduction takes place after 10 years of exclusive vegetative growth which occurs by bulbils arising at the base of the trunk.

Conservation status[edit]

Cycas species are threatened worldwide and almost all the species are listed in IUCN Redlist. Cycas beddomei is the only species of the genus Cycas listed in Appendix I of CITES. Cycas rumphii and Cycas pectinata have the most widespread distribution

List of species[edit]

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

References[edit]

  1. ^ a b c 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.
  2. ^ 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.
  3. ^ a b Kew World Checklist of Selected Plant Families
  4. ^ The World List of Cycads
  5. ^ 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.
  6. ^ 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.
  7. ^ 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.

External links[edit]

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Wikispecies has information related to Cycas.
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