Distribution of Cycas, redrawn from Jones (1993).
A seed-bearing cycad in Bowling Green National Park, Queensland [C.J. Earle, 1996.03.17].
Distribution of Cycas, redrawn from Jones (1993).
A seed-bearing cycad in Bowling Green National Park, Queensland [C.J. Earle, 1996.03.17].
Cycas
Cycads, 
[Chinese].
The sole genus in Cycadaceae Persoon. In this treatment there are 88 species, but so far there has been no comprehensive generic study. The species are listed here, with links to those species treated here.
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For species not described here, interested readers are referred to the excellent descriptions provided by The World List of Cycads.
Cycas is readily recognized by the leaflets, which have a prominent midrib and lack any obvious secondary veins. Other features useful in recognizing members of the genus include:
Trunk ovoid and subterreanean or slender to stout and emergent. Leaf bases retained on the trunk at senescence. New leaves erect with circinnate leaflets, emerging singly or in flushes, glabrous or with hairs that are shed with age. Mature leaves pinnate, oblong in outline, flat or V-shaped in cross-section, the older leaves spreading or deflexing after a flush in growth. Cataphylls prominent, arising in alternating flushes with the leaves, often rigid and pungent-tipped. Petioles swollen and hairy at the base, often with a lateral series of short, rigid, thorn-like processes borne more or less in opposite pairs, these being reduced lower leaflets. Rhachis lacking prickles, not twisted, straight or recurved in profile. Leaflets decurrent at the base, alternate to nearly opposite, with a prominent midrib, mostly evenly spaced except for the lower leaflets, straight or falcate, margins usually entire, sometimes serrulate in the distal third, lacking a callous base. Cones markedly dissimilar in shape and size. Male cones cylindrical; sporophylls arranged in a typical cone. Female cones loose and open; sporophylls arranged in a loose grouping surrounding the vegetative apex of the stem, with a linear stalk and an expanded apical lobe which may be entire, pinnatifid or deeply lobed on the margins. Ovules two to eight (rarely one) on each sporophyll, attached to the linear portion. Seeds platyspermic, ovoid to oblate, or rounded, the sarcotesta not usually brightly colored but bright red in C. taiwaniana (Jones 1993).
Southeast Asia, southern China, Malaysia, tropical Australia, Oceania, Japan, Africa, and Madagascar. Habitats vary widely, from coastal and near-coastal lowlands to interior hills and ranges. Many species grow in woodlands, a few in grasslands, and many on rocky slopes and escarpments where vegetation is sparse. Some are in areas with frequent wildfire. Some species, in arid regions, are deciduous during the dry season. Others, in coastal locales, have floating seeds that have given them a wide distribution (Jones 1993).
The Cycadaceae are, in general, very much of conservation concern. The IUCN (2020) has identified 11 taxa as critically endangered, 16 as endangered, and 30 as vulnerable. Thus 58% of all cycads are at risk. Principal factors of decline include habitat conversion through agriculture or development, illegal removal of wild plants for horticultural collection, and climate change.
Cycas angulata (heights to 12 m, diameters to 40 cm) has the greatest height to be found in the genus. The greatest diameter attained by Cycas thouarsii. Norstog and Nichols (1997) provide a photograph of a specimen in the Mauritius Botanical Garden that appears to be approximately 150 cm dbh.
See Cycadales for general notes and see species descriptions for specifics.
Generic name derived from the Greek koikas, apparently used by Theophratus for a type of palm. This was transliterated to kykas and thence to Cycas.
Cycas is viewed as the most primitive cycad genus (lower Permian of China). One fossil species has been described from the Eocene of Kyushu, Japan (Jones 1993).
IUCN. 2020. IUCN Red List version 2020-1: Table 4b: Red List Category summary for all plant classes and families. https://nc.iucnredlist.org/redlist/content/attachment_files/2020_1_RL_Stats_Table_4b.pdf, accessed 2022.09.23.
Species descriptions at the Palm and Cycad Societies of Australia home page.
Last Modified 2023-03-03
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