The genus Cycas

cycas revoluta
Cycas revoluta

The genus Cycas is the oldest, most widespread and most species-rich cycad genus on Earth. With approximately 120 accepted species ranging from eastern Africa and Madagascar through tropical and subtropical Asia, Japan, Australia and the western Pacific islands, it is the only genus in the family Cycadaceae — the sister lineage to all other living cycads (Zamiaceae). Cycas includes the most widely cultivated cycad in the world (Cycas revoluta, the sago palm), the most devastating cycad pest crisis in modern history (the Aulacaspis yasumatsui pandemic), and some of the most critically endangered plant species known to science.

For gardeners, Cycas offers the widest range of cultivation possibilities of any cycad genus: from frost-tolerant species that survive in USDA zone 8 to tropical giants that need year-round warmth. This page provides a comprehensive overview of the genus and serves as a gateway to the individual species profiles on succulentes.net.

Taxonomy and systematic position

Cycas L. is the sole genus of the family Cycadaceae, one of the two families within the order Cycadales. This makes it phylogenetically isolated: all other living cycad genera belong to the family Zamiaceae. The genus was described by Linnaeus in 1753, with Cycas circinalis as the type species.

The most comprehensive modern taxonomic treatment is that of Ken Hill (Royal Botanic Gardens Sydney), whose monographic work from the 1990s through the 2010s multiplied the number of recognised species from fewer than 30 to over 100. This expansion was driven by fieldwork across South-East Asia, where many narrow endemics were described for the first time. The World List of Cycads (Calonje, Stevenson & Stanberg) currently recognises approximately 120 species.

Distinctive characters

Cycas is distinguished from all other cycad genera by its female reproductive structures: instead of a compact, closed cone (as in Zamiaceae), female Cycas plants produce loosely arranged, leaf-like megasporophylls — modified leaves each bearing 2–8 ovules along their margins. This open arrangement is considered the most primitive reproductive morphology among living cycads and has no parallel in Zamiaceae. Male plants produce conventional pollen cones.

Geographic range and diversity

Cycas has the broadest geographic range of any cycad genus, spanning from the east coast of Africa (Mozambique, Tanzania, Kenya, Madagascar) across the Indian subcontinent (India, Sri Lanka), through South-East Asia (Myanmar, Thailand, Laos, Vietnam, Cambodia, southern China, Taiwan), into Japan (the Ryukyu Islands and Kyushu), down through the Malay Archipelago (Philippines, Indonesia, Borneo, Sulawesi, Timor), New Guinea, and across to northern and north-eastern Australia and numerous Pacific islands (Tonga, Fiji, New Caledonia, Vanuatu, Micronesia).

The centre of species diversity lies unambiguously in mainland South-East Asia and southern China, particularly in Vietnam, southern China (Yunnan, Guizhou, Guangxi, Hainan) and northern Thailand, where dozens of narrow endemics occur in limestone karst landscapes and montane forests.

Ecological diversity

Cycas species occupy a remarkable range of habitats: coastal strand and sand dunes (Cycas rumphii, Cycas thouarsii), lowland tropical rainforest understoreys (Cycas clivicola, Cycas siamensis), montane pine-oak forests (Cycas pectinata, Cycas panzhihuaensis), limestone karst (Cycas micholitzii, Cycas debaoensis), seasonally dry savanna and open woodland (Cycas media, Cycas armstrongii), and even mangrove margins (Cycas thouarsii). This ecological breadth is unmatched by any other cycad genus.

Conservation and threats

IUCN status

A high proportion of Cycas species are threatened. Many of the recently described South-East Asian endemics have extremely restricted ranges — sometimes a single limestone hill or a few square kilometres of forest — and are classified as Endangered (EN) or Critically Endangered (CR). Species such as Cycas beddomei (India), Cycas micholitzii (Vietnam) and Cycas multipinnata (China) face severe pressure from habitat loss and illegal collection.

CITES

All Cycas species are listed under CITES Appendix II, meaning international trade requires export permits and proof of legal, sustainable sourcing. Cycas beddomei is listed under CITES Appendix I — the highest level of protection, prohibiting commercial trade in wild specimens.

The Aulacaspis yasumatsui crisis

The cycad aulacaspis scale (Aulacaspis yasumatsui Takagi), a tiny armoured scale insect native to South-East Asia, has become the single most devastating pest ever to afflict cycads. First detected outside its native range in Florida in 1996, it has since spread to Hawaii, the Caribbean, parts of Africa and numerous Pacific islands. It preferentially attacks Cycas species, covering leaves, trunks and even seed integuments in a dense white crust of female scales. Heavily infested plants die within months. Research by Marler et al. has shown that direct seed infestation reduces germination by two-thirds and kills over half of resulting seedlings. The pest has caused catastrophic declines in wild populations of Cycas micronesica (Guam, Mariana Islands) and threatens ex situ collections worldwide.

Biological control agents — particularly the predatory beetle Rhyzobius lophanthae and the parasitoid wasp Coccobius fulvus — have shown promise in some regions but have not eliminated the pest. Systemic insecticides (imidacloprid, dinotefuran) remain the most effective treatment for cultivated plants.

Cultivation

Light

Most Cycas species prefer full sun to bright partial shade. Cycas revoluta tolerates a wide range of light conditions, from full sun to relatively deep shade, which partly explains its ubiquity in cultivation. Forest-dwelling species (Cycas clivicola, Cycas siamensis) prefer filtered light. As a general rule, species from open habitats (savannas, coastal dunes, limestone ridges) want more sun than species from forest understoreys.

Temperature and cold hardiness

Cold tolerance varies enormously across the genus:

  • Hardy (−8 to −12 °C, USDA zone 8a–8b): Cycas revoluta (the hardiest widely available species; leaf damage below −8 °C, stem-hardy to −10/−12 °C in dry soil), Cycas panzhihuaensis (possibly the hardiest Cycas, tolerating −10 to −15 °C in its native habitat at 1,200–2,500 m in Yunnan/Sichuan).
  • Semi-hardy (−3 to −6 °C, USDA zone 9a–9b): Cycas taitungensis, Cycas media, Cycas multipinnata.
  • Tender (0 to −2 °C, USDA zone 10): Cycas rumphii, Cycas thouarsii, Cycas circinalis, Cycas beddomei and most tropical Asian and Pacific species.

As with all cycads, dry soil in winter dramatically improves cold tolerance. A Cycas revoluta in well-drained, rocky ground may survive −10 °C, while the same plant in waterlogged clay may die at −5 °C.

Substrate

Drainage is paramount. All Cycas species require a well-drained, aerated substrate. For in-ground planting, amend heavy soils with pumice, coarse sand, volcanic gravel or perlite. In pots, use a mix of approximately 50–60% mineral material (pumice, perlite, coarse sand) and 40–50% organic material (pine bark, coco coir). Avoid peat-heavy mixes that retain excessive moisture. Soil pH is generally not critical — most species tolerate slightly acidic to slightly alkaline conditions — but limestone-dwelling species (Cycas micholitzii, Cycas debaoensis) benefit from calcareous amendments.

Watering

Moderate watering during the growing season (spring–autumn), with thorough drying between irrigations. Reduce watering substantially in winter, especially for pot-grown plants and in cold climates. Overwatering is the most common cause of death in cultivated Cycas. Less water is better.

Propagation

Pollination

Cycas is dioecious: male and female plants must be present for seed production. In cultivation, hand pollination is standard practice. Pollen is collected from mature male cones by gently shaking or brushing microsporophylls over a clean container. Fresh pollen is dusted onto receptive ovules of the megasporophylls using a soft brush or puffer bottle. Pollen viability declines rapidly; use within 24–48 hours or store desiccated pollen frozen (−18 °C) for up to several months.

Seed maturation

After pollination, seeds develop over 12–18 months (sometimes longer). Mature seeds are large (2–5 cm depending on species), with a fleshy, often brightly coloured outer layer (sarcotesta) — red, orange or yellow — overlying a hard, bony inner layer (sclerotesta) protecting the embryo. Some species (Cycas thouarsii, Cycas rumphii) produce buoyant seeds adapted for oceanic dispersal.

Seed preparation

Remove the fleshy sarcotesta completely before sowing — it contains germination inhibitors and promotes fungal growth. Wear gloves (the sarcotesta is mildly toxic and irritating). Soak the cleaned seeds in warm water for 24–72 hours. Desiccated seeds may rattle slightly within the shell; this does not necessarily indicate loss of viability, but fresh seed gives the best results. A float test can help assess viability: most viable Cycas seeds sink (exception: the oceanic-dispersal species Cycas thouarsii, Cycas rumphii and Cycas edentata float naturally).

Advanced techniques for accelerating germination include scarification of the sclerotesta with concentrated sulphuric acid (H₂SO₄) and soaking in gibberellic acid (GA₃) solution to break physiological dormancy and promote embryo development. These methods are described in the scientific literature (e.g., Dehgan & Johnson, Huntington Botanical Gardens protocols) but require care and chemical safety precautions.

Sowing

Use a free-draining mix of coarse perlite, pumice, coarse sand or coco coir. Bury seeds only halfway in the medium — the upper half should remain exposed. Cover the container with clear plastic to maintain humidity. No light is required during germination. Maintain temperatures of 25–30 °C (rarepalmseeds.com). Check weekly for root emergence through the drainage holes or by gently pressing the seed. Most Cycas species germinate in 4–12 weeks, though some require longer (up to several months). After the root emerges, move the seedling into a tall, narrow pot with a well-drained mix and provide bright indirect light.

Raising seedlings

Seedling growth is very slow — expect one to two flushes of leaves per year in the first years. Provide bright light (full sun for savanna species, filtered light for forest species), moderate warmth, and careful watering (moist but never wet). A slow-release fertiliser applied once or twice per year supports growth. Protect seedlings from frost, slugs and snails. Seedlings of most species can be moved to their permanent position after 2–3 years when a sturdy caudex has developed.

Vegetative propagation

Some Cycas species produce basal offsets (suckers) that can be separated from the parent plant. Allow the offset to develop several leaves and ideally some roots before detachment. Let the wound dry for several days before potting in a well-drained mix. Cycas revoluta is the species most commonly propagated by offsets. Stem cuttings are not a reliable method for most species.

Pests and diseases

Cycad aulacaspis scale (Aulacaspis yasumatsui) — the most serious threat. White, armoured scale covering leaves and trunk. Can kill mature plants. Treat with systemic insecticides (imidacloprid, dinotefuran) applied as a soil drench. Monitor regularly. Quarantine new acquisitions.

Mealybugs — occasional, particularly on pot-grown plants. Treat with isopropyl alcohol, horticultural oil or systemic insecticide.

Cycad blue butterfly (Chilades pandava) — larvae feed on emerging leaves, causing severe defoliation. A serious pest in South-East Asia, Australia and increasingly in Mediterranean regions where Cycas revoluta is planted. Hand-pick larvae or treat with Bacillus thuringiensis (Bt).

Root and crown rot — caused by Phytophthora, Fusarium and Pythium in waterlogged conditions. Prevention: drainage. No effective cure once established.

Leaf spot and algal leaf spot — cosmetic in most cases. Improve air circulation and reduce overhead watering.

Species of Cycas

The following list includes all species currently accepted by Plants of the World Online (POWO) and/or the World List of Cycads. Species are arranged by geographic and taxonomic affinity following the infrageneric sections of Ken Hill (1995–2008), simplified here into five practical groups reflecting both phylogenetic relationships and horticultural relevance. Species with a particularly notable horticultural profile are briefly annotated.

East Asian species (Japan, China, Taiwan)

This group includes the hardiest Cycas species and the most important for European gardens. It corresponds broadly to Hill’s sections Asiorientales and Panzhihuaenses. These species originate from temperate to warm-temperate climates with significant seasonal cold, making them the best candidates for outdoor cultivation in Mediterranean and oceanic Europe.

South-East Asian mainland species (Indochina, India, Sri Lanka)

A large and taxonomically complex group, corresponding broadly to Hill’s sections Indosinenses and Stangerioides. These are primarily tropical to subtropical species of forest understoreys, limestone karst and seasonally dry woodlands. Most are frost-tender.

  • Cycas circinalis — queen sago; India (Malabar Coast, Western Ghats); the type species of the genus; large, arborescent; frost-tender
  • Cycas beddomei — Beddome’s cycad; Andhra Pradesh, India; Critically Endangered; the only Cycas on CITES Appendix I
  • Cycas indica — India
  • Cycas nathorstii — India
  • Cycas spherica — India
  • Cycas zeylanica — Sri Lanka
  • Cycas siamensis — Thailand, Myanmar, Laos, Vietnam; widespread in seasonally dry woodlands; swollen, bottle-shaped caudex base
  • Cycas pectinata — Himalayan cycad; India (north-east), Myanmar, Thailand, Laos, Vietnam, southern China; montane species to 1,500 m; one of the hardier tropical species
  • Cycas simplicipinna — Yunnan (China), Thailand, Laos, Vietnam, Myanmar
  • Cycas clivicola — Thailand; limestone cliff specialist
  • Cycas chamaoensis — Thailand
  • Cycas nongnoochiae — Thailand; named after Nong Nooch Tropical Garden
  • Cycas elephantipes — Thailand
  • Cycas micholitzii — Vietnam; section Stangerioides; distinctive soft-textured cones; sought-after collector’s species
  • Cycas chevalieri — Vietnam
  • Cycas hoabinhensis — Vietnam
  • Cycas lindstromii — Vietnam
  • Cycas collina — Vietnam, southern China
  • Cycas candida — Vietnam; recently described
  • Cycas jenkinsiana — north-eastern India, Myanmar

Malesian, Philippine and Pacific Island species

Species from the Malay Archipelago, the Philippines, New Guinea and the Pacific islands. Includes Hill’s section Wadeae (Philippines) and the oceanic-dispersal species of section Cycas (formerly Rumphiae group), characterised by buoyant seeds with spongy endotesta adapted for dispersal by ocean currents. All are tropical and frost-tender.

  • Cycas rumphii — queen sago; widespread from Sulawesi to New Guinea and the Moluccas; buoyant seeds; large arborescent species
  • Cycas edentata — Philippines, Indonesia; buoyant seeds; variable species complex
  • Cycas wadei — Culion Island, Philippines; section Wadeae; Critically Endangered
  • Cycas riuminiana — Philippines
  • Cycas falcata — Sulawesi, Indonesia
  • Cycas sundaica — Java, Lesser Sunda Islands
  • Cycas montana — Sulawesi, Indonesia
  • Cycas javana — Java, Indonesia
  • Cycas papuana — New Guinea
  • Cycas scratchleyana — New Guinea
  • Cycas apoa — New Guinea
  • Cycas bougainvilleana — Bougainville, Solomon Islands
  • Cycas seemannii — Fiji, Tonga, Vanuatu, New Caledonia; the most widely distributed Pacific island species
  • Cycas micronesica — Guam, Mariana Islands, Palau, Yap; Endangered; devastated by Aulacaspis yasumatsui

Australian species

Australia harbours approximately 27–34 Cycas species — the largest national concentration in the genus. These are primarily tropical to warm-temperate species of savanna, open woodland and monsoon vine thickets in Queensland, the Northern Territory and Western Australia. The southernmost species (Cycas megacarpa, ~26°S) extends into subtropical south-eastern Queensland. Several Australian species are important in cultivation.

  • Cycas media — widespread across northern Australia (Queensland, Northern Territory); the most commonly cultivated Australian Cycas; savanna and open woodland; hardy to −3/−5 °C
  • Cycas megacarpa — south-eastern Queensland; the southernmost Cycas in Australia (~26°S); large seeds; Endangered
  • Cycas ophiolitica — central Queensland; serpentinite specialist; Endangered
  • Cycas armstrongii — Northern Territory; deciduous (loses leaves in dry season); fire-adapted; widespread in savanna
  • Cycas calcicola — Northern Territory; limestone specialist
  • Cycas canalis — Northern Territory
  • Cycas maconochiei — Northern Territory
  • Cycas angulata — Queensland, Northern Territory
  • Cycas brunnea — Queensland
  • Cycas cairnsiana — Queensland; blue-leaved; ornamental
  • Cycas couttsiana — Queensland
  • Cycas desolata — Northern Territory
  • Cycas furfuracea — Queensland
  • Cycas lane-poolei — Western Australia
  • Cycas normanbyana — Queensland; the “hope’s cycad” of some older references
  • Cycas platyphylla — Queensland
  • Cycas pruinosa — Northern Territory, Western Australia
  • Cycas silvestris — Queensland
  • Cycas tuckeri — Queensland
  • Cycas yorkensis — Cape York, Queensland
  • Cycas xipholepis — Queensland
  • Cycas badensis — Queensland
  • Cycas terryana — Queensland
  • Cycas semota — Northern Territory
  • Cycas basaltica — Western Australia
  • Cycas conferta — Northern Territory

African and Indian Ocean species

A single species represents the westernmost outpost of the genus — a remarkable biogeographic outlier.

  • Cycas thouarsii — Comoros, Madagascar, coastal Tanzania, Mozambique, Kenya, Seychelles; the only African Cycas; large arborescent species with buoyant seeds; coastal habitats; frost-tender

Authority websites and online databases

The Cycad Pages — Royal Botanic Gardens Sydney
The most comprehensive online taxonomic resource for Cycas, maintained by Ken Hill and subsequently by the Royal Botanic Gardens. Includes descriptions, distribution maps and photographs for all species.
https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/cycadpg?taxname=Cycas

World List of Cycads
The standard taxonomic checklist for all cycad genera, including Cycas.
https://www.cycadlist.org/

IUCN SSC Cycad Specialist Group
Conservation status updates, annual reports, and the newsletter CYCADS.
https://www.cycadgroup.org/

The IUCN Red List of Threatened Species
Detailed assessments for all Cycas species.
https://www.iucnredlist.org/

Plants of the World Online (POWO) — Royal Botanic Gardens, Kew
Accepted names, synonymy and distribution for all Cycas species.
https://powo.science.kew.org/

CITES Species+ Database
Trade regulations and listing status for all Cycas species.
https://speciesplus.net/

rarepalmseeds.com — Germinating Cycads
Practical seed germination instructions from one of the leading cycad seed suppliers.
https://www.rarepalmseeds.com/germinating-cycads

Bibliography

Hill, K.D. — numerous publications on the taxonomy of Cycas, including “The Cycas rumphii complex” (2004), “The genus Cycas in China” (2008) and many species descriptions. The foundational modern taxonomic work on the genus.

Jones, D.L. — Cycads of the World. 2nd edition. Smithsonian Institution Press, 2002. The standard comprehensive reference; includes all Cycas species known at the time of publication.

Whitelock, L.M. — The Cycads. Timber Press, 2002. Excellent for habitat ecology and field observations.

Marler, T.E., Lindström, A.J. & Watson, G.W. — “Aulacaspis yasumatsui delivers a blow to international cycad horticulture.” Horticulturae, various publications (2020–2023). Essential reading on the aulacaspis scale crisis and its impact on Cycas conservation and propagation.

Nagalingum, N.S. et al. — “Recent synchronous radiation of a living fossil.” Science 334 (2011): 796–799. The landmark molecular phylogenetic study showing that living Cycas species diversified recently despite the ancient lineage.

Donaldson, J.S. (ed.) — Cycads: Status Survey and Conservation Action Plan. IUCN/SSC Cycad Specialist Group, 2003.

Dehgan, B. & Johnson, C.R. — “Improved seed germination of Zamia floridana with H₂SO₄ and GA₃.” Scientia Horticulturae 19 (1983): 37–43. Classic reference for chemical seed treatment techniques applicable across cycad genera.

IUCN SSC Cycad Specialist Group — Annual reports (2016–2025) and Handbook of Cycad Cultivation and Landscaping, 2nd edition. Available at https://www.cycadgroup.org/.