Cycadaceae

Wikipedia links:       Gymnosperms > Cycadales > Cycadaceae > Cycas

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Common name:         Cycads

Conservation status: unkown

• 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

• Cycas rumphii and Cycas pectinata have the most widespread distribution

Etymology:   

Cones and seed:                              

• 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

• Megasporophylls are not gathered in cones

• Pollination takes place by air.

• Cycas 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

Leaves:         

• 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

Stem & branches: 

• Most species form distinct branched or unbranched trunks

• In some species the main trunk can be subterranean with the leaf crown appearing to arise directly from the ground

Roots:         

Habit:        

Habitat:   

Distribution:                  

• 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

Species:

• About 113 species are accepted, which are native to the Indo-Pacific, East Africa and Madagascar

Additional notes:     

• Cycas is a genus of cycad, and the only genus in the family Cycadaceae

• Evolution

  • 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 to the Carboniferous

  • 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

  • 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 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

  • 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