cycas

''Cycas'' is a genus of plants belonging to a very ancient lineage, the Cycadophyta, which are not closely related to palms, ferns, trees or any other modern group of plants. They are evergreen perennials which achieved their maximum diversity in the Jurassic and Cretaceous periods, when they were distributed almost worldwide. At the end of the Cretaceous, when the non-avian dinosaurs became extinct, so did most of the cycas in the Northern Hemisphere.

''Cycas'' is the type genus and the only extant genus recognised in the family Cycadaceae. About 113 species are accepted. ''Cycas circinalis'', a species endemic to India, was the first cycad species to be described in western literature, and was the type of the generic name, ''Cycas''. The best-known ''Cycas'' species is ''Cycas revoluta''.

Range

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.Kew World Checklist of Selected Plant Families
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Evolution

''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. 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. 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.

Morphology

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

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

''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

*'' Cycas aculeata''
*'' Cycas aenigma''
*''Cycas angulata''
*'' Cycas annaikalensis''
*'' Cycas apoa''
*'' Cycas arenicola''
*'' Cycas armstrongii''
*'' Cycas arnhemica''
*''Cycas badensis''
*'' Cycas balansae''
*'' Cycas basaltica''
*'' Cycas beddomei''
*'' Cycas bifida''
*'' Cycas bougainvilleana''
*'' Cycas brachycantha''
*'' Cycas brunnea''
*'' Cycas cairnsiana''
*'' Cycas calcicola''
*'' Cycas campestris''
*'' Cycas canalis''
*'' Cycas candida''
*'' Cycas cantafolia''
*'' Cycas chamaoensis''
*''Cycas changjiangensis''
*'' Cycas chenii''
*'' Cycas chevalieri''
*''Cycas circinalis''
*'' Cycas clivicola''
*''Cycas collina''
*'' Cycas condaoensis''
*'' Cycas conferta''
*'' Cycas couttsiana''
*'' Cycas cupida''
*'' Cycas curranii''
*'' Cycas debaoensis''
*'' Cycas desolata''
*'' Cycas diannanensis''
*'' Cycas distans'' P.I.Forst. & B.Gray
*'' Cycas dolichophylla''
*'' Cycas edentata''
*'' Cycas elephantipes''
*'' Cycas elongata''
*'' Cycas falcata''
*'' Cycas fairylakea''
*'' Cycas ferruginea''
*''Cycas fugax''
*'' Cycas furfuracea''
*'' Cycas glauca''
*'' Cycas guizhouensis''
*'' Cycas hainanensis''
*''Cycas hoabinhensis''
*'' Cycas hongheensis''
*''Cycas indica'' (=''Cycas swamyi'')
*'' Cycas inermis''
*''Cycas javana''
*'' Cycas lacrimans''
*'' Cycas lane-poolei''
*'' Cycas lindstromii''
*'' Cycas litoralis''
*'' Cycas maconochiei''
*'' Cycas macrocarpa''
*''Cycas media''
*'' Cycas megacarpa''
*'' Cycas micholitzii''
*'' Cycas micronesica''
*'' Cycas montana''
*'' Cycas multipinnata''
*'' Cycas nathorstii''
*'' Cycas nayagarhensis''
*''Cycas nitida''
*'' Cycas nongnoochiae''
*'' Cycas ophiolitica''
*'' Cycas orientis''
*'' Cycas orixensis''
*'' Cycas pachypoda''
*'' Cycas panzhihuaensis''
*''Cycas papuana''
*'' Cycas pectinata''
*'' Cycas petraea''
*'' Cycas platyphylla''
*'' Cycas pranburiensis''
*'' Cycas pruinosa''
*''Cycas revoluta'' (Sago palm)
*'' Cycas riuminiana''
*''Cycas rumphii'' Miq.
*'' Cycas sancti-lasallei''
*'' Cycas sainathii''
*'' Cycas saxatilis''
*'' Cycas schumanniana''
*'' Cycas scratchleyana''
*''Cycas seemannii'' A.Braun
*'' Cycas segmentifida''
*'' Cycas semota''
*'' Cycas sexseminifera''
*'' Cycas shanyaensis''
*'' Cycas siamensis''
*''Cycas silvestris''
*'' Cycas simplicipinna''
*'' Cycas sphaerica''
*'' Cycas sundaica''
*'' Cycas szechuanensis''
*'' Cycas taitungensis''
*'' Cycas taiwaniana''
*'' Cycas tanqingii''
*''Cycas tansachana''
*'' Cycas thouarsii''
*'' Cycas tropophylla''
*'' Cycas tuckeri''
*'' Cycas vespertilio''
*''Cycas wadei''
*'' Cycas xipholepis''
*'' Cycas yorkiana''
*'' Cycas yunnanensis''
*'' Cycas zambalensis''
*'' Cycas zeylanica''

References

External links

*
*Hill, K.D.(1998–2004) The Cycad Pages, Royal Botanic Gardens Sydney. http://plantnet.rbgsyd.nsw.gov.au/PlantNet/cycad/index.html
Virtual Cycad Encyclopedia
edited by the Palm & Cycad Societies of Florida
*David, J. de Laubenfels
Cycas Taxonomy
*
*
*Singh, R & JS Khuraijam (2013-) Cycads of India. http://www.cycadsofindia.in/
*
*
*Terrence Walters & Roy Osborne (eds.) (2004), ''Cycad Classification: Concepts and Recommendations'', CABI publishing,
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