Cycas chamaoensis

Cycas chamaoensis is a large cycad from south-eastern Thailand that grows only on the granite cliffs of Khao Chamao, a mountain in Rayong Province protected within Khao Chamao-Khao Wong National Park. Described in 1999 by the Australian botanist Ken Hill, this member of the genus Cycas can build a trunk 10 m tall and carries orange male cones up to 60 cm long. The IUCN lists it as Critically Endangered, mainly because wild plants have been dug up for gardens; yet it is also the native cycad most widely sold in Thailand, and the only one there grown in quantity from nursery stock.

Key facts about Cycas chamaoensis

  • Accepted name: Cycas chamaoensis K.D.Hill (1999), accepted by The World List of Cycads (version 2026.08.15); the World Checklist of Vascular Plants (WCVP), on which POWO is based, also accepts it (consulted through GBIF on 31 October 2026)
  • Former names and synonyms: none
  • Family: Cycadaceae, order Cycadales
  • Common names: no English name attested; in Thai ปรงเขาชะเมา (see Common names)
  • Natural range: south-eastern Thailand, the Khao Chamao massif only (Rayong Province; The World List of Cycads gives neighbouring Chanthaburi Province)
  • IUCN status: Critically Endangered (CR A2ad; B1ab(i,ii,iv,v); C2a(i); D), assessment by A. Lindström published in 2022; already CR in 2010
  • CITES and other protection: CITES Appendix II; Annex B in the European Union; protected in Thailand under the Plant Varieties Act of 1975 (B.E. 2518)
  • Documented hardiness: no measured value; a British nursery places it in USDA zone 9b, without cultivation data to back it up (see Cold hardiness)
  • Light and soil: in the wild, crevices in bare granite outcrops and cliffs, in full sun
  • Habit and adult size: trunk erect or leaning, up to 10 m; often more than 60 leaves, 1.2 to 2.5 m long, in the crown
  • In the UK, US and Australia: two accessions at Montgomery Botanical Center (Florida), from 1994 and 1995 judging by their numbers; listed by the University of Hawaii at Hilo in BGCI PlantSearch; no record in British or Australian gardens (see In cultivation in the UK, US and Australia)
  • Toxicity: no analysis specific to the species; treat it as poisonous, like all Cycas (see Toxicity and precautions)

How to recognise Cycas chamaoensis

It is a big, trunk-forming cycad with a very full crown of long leaves, and the male plants bear orange cones among the largest in the genus. The original description by Hill and Yang (Brittonia, 1999) sits behind a paywall and could not be read. The characters below therefore come from the profile published by the Palm and Cycad Societies of Australia (PACSOA), from the comparative table of Jutta and colleagues (2010) and, for the finer measurements of leaves and cones, from the English Wikipedia article, the only source available for those figures:

  • Trunk: tree-like, erect or leaning, up to 10 m, usually single (PACSOA, Wikipedia).
  • Leaves: numerous, often more than 60 in the crown, green to grey-green, semi-glossy and leathery, 1.2 to 2.5 m long, ending in a spine (PACSOA; spine according to Wikipedia).
  • Petiole: 30 to 60 cm, hairless, spiny along part of its length (Wikipedia).
  • Leaflets: 85 to 155 pairs, lance-shaped, hairless, angled forwards at 60 to 70° to the rachis (Wikipedia).
  • Male cones: single, upright, spindle-shaped to narrowly ovoid, 50 to 60 cm long and 12 to 13 cm across, orange, each scale ending in a conspicuous spine (Wikipedia).
  • Megasporophylls: 13 to 18 cm, with yellow to grey down, bearing 2 to 4 ovules; blade almost round, deeply comb-like, with 30 to 40 lateral spines up to 30 mm long (Wikipedia; Jutta and colleagues 2010 for the shape of the blade and the spines).
  • Seeds: flattened-ovoid, 35 to 40 mm by 30 to 40 mm; yellow sarcotesta about 3 mm thick, with a fibrous layer; smooth sclerotesta (Jutta and colleagues 2010; Wikipedia for colour and thickness).

Jutta and colleagues (2010) group the species with the cycads whose female cone is of the “closed type”, alongside Cycas tansachana, Cycas clivicola and Cycas cantafolia.

Hybrids

No hybrid, natural or garden-made, is documented.

Possible confusion

The main risk of confusion is with the other Thai and Malaysian cycads that have a closed female cone, and with a few Thai cycads common in cultivation:

  • Cycas tansachana, another Thai endemic with a closed cone, from the limestone cliffs of Saraburi and Lopburi provinces: Jutta and colleagues (2010) separate it by habitat and by details of the leaves and sporophylls;
  • Cycas cantafolia, its closest relative in Peninsular Malaysia, which also grows on granite: its megasporophyll blade is oval rather than almost round, with fewer (25 to 30) and shorter (18 mm at most) lateral spines;
  • Cycas clivicola, another closed-cone cycad with a round blade, which Jutta and colleagues (2010) compare with the three species above;
  • Cycas pectinata, widespread in mainland Asia, which PACSOA presents as a close relative of Cycas chamaoensis; the published sources do not give the characters that separate them;
  • Cycas elephantipes, endemic to Chaiyaphum Province in north-eastern Thailand, on sandstone rocks: the Thai Department of Agriculture describes it with a strongly swollen trunk base, like an “elephant’s foot”.

Taxonomy

Cycas chamaoensis is a name accepted by The World List of Cycads, with no synonym; the World Checklist of Vascular Plants (WCVP), on which POWO is based, also accepts it (consulted through GBIF on 31 October 2026). Ken Hill described the species in the revision of the genus in Thailand that he co-authored with S. L. Yang, “The genus Cycas (Cycadaceae) in Thailand”, published in Brittonia 51(1): 48–73 in 1999. The description is on pages 58 to 60, with figure 6, and the name is attributed to Hill alone.

The type is the collection Hill & Vatcharakorn 4617, made on 16 April 1994 on the steep north-western slopes of Khao Chamao, in Rayong Province. The holotype is kept at the National Herbarium of New South Wales in Sydney (NSW), with isotypes in Bangkok (BKF), at Kew (K), Leiden (L) and Beijing (PE).

Jutta and colleagues (2010) place the species in section Indosinenses. The name has not changed since publication.

Etymology and history

The epithet chamaoensis refers to Khao Chamao, the mountain in Rayong Province that is both the type locality and the only known habitat of the species (Haynes 2022, cited by The World List of Cycads).

Its recent history is one of conservation. On 15 and 16 February 2023, at the request of Khao Chamao-Khao Wong National Park, six specialists from Nong Nooch Tropical Garden, near Pattaya, and six park rangers surveyed the only known population. The project, named ACREE (Assisted Reproduction of the Critically Endangered and Endemic Cycas chamaoensis), is funded by the Mohamed bin Zayed Species Conservation Fund and involves the IUCN Cycad Specialist Group and Anders Lindström of Nong Nooch. The park’s drones made it possible to search cliffs that cannot be reached on foot: the plants turned out to be numerous, and an insect not yet identified was seen acting as the natural pollinator. Samples were sent to Liu Jian, of the Kunming botanic garden, for a study of genetic diversity by RADseq.

Common names

No English common name is attested: the British nursery Trebrown gives “None known”. In Thailand the species is called ปรงเขาชะเมา, which can be transliterated prong khao chamao (“cycad of Khao Chamao”); the name appears in the Thai Biodiversity Information Facility (THBIF), in the Thai Department of Agriculture’s report on cycads and in the Nong Nooch press release, which also uses the short form ปรงชะเมา.

In the wild

Cycas chamaoensis grows only on the Khao Chamao massif in south-eastern Thailand. According to the Thai Department of Agriculture (2019), it occupies the exposed granite cliffs of the Khao Chamao range, inside Khao Chamao-Khao Wong National Park, Khao Chamao district (Rayong Province). The PACSOA profile places the mountain north-east of Klaeng and says that the plant grows in crevices in bare granite outcrops, usually in full sun; Jutta and colleagues (2010) give “bare rock on slopes and cliffs” north-east of Ban Nam Sae.

The World List of Cycads gives Chanthaburi Province as its distribution, whereas the type label, the Thai report and the PACSOA profile all place the population in Rayong Province. No published source explains the discrepancy.

The park, created in 1975, covers only 84 km². In this part of Thailand the rainy season runs from May to October, the cool season from November to February and the hot season from March to April (Thai National Parks). For pollination, the only published observation is the unidentified insect seen during the 2023 survey.

One error is in circulation: the text of the paper by Jutta and colleagues (2010) calls the species “restricted to limestone”, while the table in the same paper, the PACSOA profile and the Thai report all give granite. Granite is the substrate to retain.

Conservation status and regulation

Cycas chamaoensis is listed as Critically Endangered (CR) by the IUCN. The first assessment, by K. D. Hill, dates from 2010; the current one, by A. Lindström, was published in 2022 under criteria A2ad; B1ab(i,ii,iv,v); C2a(i); D, according to The World List of Cycads, and the CR category is confirmed by the IUCN data relayed by GBIF (consulted on 13 October 2026). These criteria reflect a population decline, a tiny range that keeps shrinking and a very small number of plants; for the CR category, criterion D means fewer than 50 mature individuals estimated. The 2023 survey nevertheless found more plants than expected.

The main threat is the removal of wild plants. The Thai Department of Agriculture, which studied the country’s cycads from 2015 to 2019 to set the conditions for their export (a CITES non-detriment finding), found signs of illegal collecting in natural populations. It ranks Cycas chamaoensis as the second most threatened species in the country after Cycas tansachana, because it is promoted as the Thai cycad with the densest, most handsome foliage and the fastest growth. Like the other endemics, it also has a limited natural capacity for dispersal.

The same report notes an encouraging exception: Cycas chamaoensis is the only Thai cycad also sold as nursery-propagated plants, the only one whose harvesting is managed locally in favour of propagation and, with Cycas siamensis, the only one that Thailand allows to be exported. Exported plants must come from a nursery registered with the Department of Agriculture and have a basal circumference of less than 15 cm, as evidence of cultivated origin. In Thailand, all native cycads are protected under the Plant Varieties Act of 1975 (B.E. 2518).

Like every species in the genus except Cycas beddomei, it is listed in CITES Appendix II, where the family Cycadaceae has been included since 4 February 1977. Annotation #4 exempts seeds in particular, whereas live plants need an export permit. The United Kingdom, the United States and Australia apply CITES through their own national legislation; in the European Union the species is in Annex B of Regulation (EC) No 338/97, whose annexes in force are set by Commission Regulation (EU) 2026/1383, applicable since 29 June 2026. Species+ confirms this status (consulted on 12 October 2026). This general information does not replace the official texts: check the rules in force before any purchase or exchange, and prefer plants raised from seed in cultivation.

Growing Cycas chamaoensis

In short: a sought-after garden plant in Thailand, a rare collector’s plant elsewhere, with no published cultivation protocol. In Thailand it is the native cycad most present in the domestic trade, and local growers raise it from seed and from offsets (Thai Department of Agriculture, 2019).

Outdoor and in-ground cultivation

The few published indications agree. The PACSOA profile recommends a sunny, well-drained position and describes the plant as a “vigorous grower”; in Thailand it is promoted as the fastest-growing native cycad. Its habitat, crevices in bare granite in full sun, confirms that it needs plenty of light and a mineral soil that does not hold water. Outdoors, that points to tropical and frost-free subtropical gardens; no in-ground trial outside Thailand has been published, in Florida, California, Australia or Europe. A mature plant, with a crown of more than 60 leaves up to 2.5 m long, needs a lot of room.

Container cultivation

Outside the tropics it is a plant for a pot under glass, at least while young: a very free-draining mineral mix, maximum light and a frost-free winter are the prudent course, though no grower has published results for the species. In France, the only trace found is on the Fous de palmiers forum: a grower who keeps a glasshouse offered about fifteen seeds brought back from Thailand for exchange in September 2009, then four germinated seeds in February 2010. No later cultivation result was published, and the Jardin zoologique tropical at La Londe-les-Maures, on the French Mediterranean coast, has published nothing on the species.

In cultivation in the UK, US and Australia

In short: very rare in public collections outside Thailand. A garden listed in the BGCI PlantSearch database (consulted in October 2026) has declared the species at some point, which does not prove that a living plant is there today.

  • United States: the online catalogue of Montgomery Botanical Center (Coral Gables, Florida) lists two accessions of Cycas chamaoensis, whose numbers point to 1994 and 1995. The Botanical Garden at the University of Hawaii at Hilo lists the species in BGCI PlantSearch.
  • Australia: none of the online catalogues consulted (Royal Botanic Garden Sydney, Mount Annan, Royal Botanic Gardens Victoria) lists the species, and no Australian garden declares it in BGCI PlantSearch.
  • United Kingdom: no British garden lists the species. The Trebrown nursery offers it with a USDA zone rating (see Cold hardiness).

No report from a grower in the United Kingdom, the United States or Australia has been published on English-language forums.

Propagation

Like all Cycas, Cycas chamaoensis is dioecious: a male and a female plant are needed to obtain fertile seed. In Thailand it is propagated from seed and by separating offsets, and the Department of Agriculture’s report stresses that local producers know how to raise plants in numbers, unlike for the country’s other cycads. No germination data specific to the species has been published. Seeds are exempt from CITES under annotation #4; ask for seed from cultivated plants.

Pests and diseases

No data specific to the species is documented. Like every cultivated Cycas, it is exposed to the Asian cycad scale, Aulacaspis yasumatsui, and to root rot in a substrate that stays too wet.

Cold hardiness

There is no measured cold-tolerance data for Cycas chamaoensis. The British nursery Trebrown places it in USDA zone 9b, that is, an average annual minimum of −3.9 to −1.1 °C (25 to 30 °F), but this is a commercial rating, given to many other tropical cycads as well, with no cultivation observation behind it. No forum post reports a temperature that the species has survived.

The species lives under a tropical monsoon climate with a cool season from November to February, but no source gives the minimum temperatures of its habitat. No dated cultivation result exists outside Thailand. In the south of France, whose Mediterranean climate is close to that of California or southern Australia, the only plants mentioned on the Fous de palmiers forum were seedlings under glass, and the Jardin zoologique tropical has no observation to offer. Bear in mind, too, that an adult plant with a tall aerial trunk does not enjoy the protection that the soil gives to young seedlings. Without data, keep it in a pot, frost-free.

Toxicity and precautions

No toxicity analysis specific to Cycas chamaoensis is documented, but the risk is well documented in the genus: in Cycas, all parts of the plant are poisonous, and the seeds above all. They contain cycasin, which is converted during digestion into methylazoxymethanol, toxic to the liver and nervous system, along with a neurotoxic amino acid, BMAA. The ASPCA lists the sago palm (Cycas revoluta) among plants poisonous to dogs, cats and horses, with vomiting, diarrhoea that may be bloody, jaundice and liver damage that can be fatal. Wear gloves to handle the seeds and their flesh, pick up fallen seeds and keep plants and seeds out of reach of children and pets. If any part is swallowed, contact a poison centre, a doctor or a vet straight away.

Traditional uses

The published sources describe no traditional food or medicinal use of Cycas chamaoensis. The only documented use is ornamental: the species is much sought after for gardens in Thailand, and the Department of Agriculture regards collecting for that purpose as a danger to the natural populations.

Frequently asked questions

Where does Cycas chamaoensis grow?

Only in Thailand, on the granite cliffs of the Khao Chamao massif in Rayong Province, within Khao Chamao-Khao Wong National Park. It should not be confused with Cycas elephantipes, which lives in Chaiyaphum Province.

Does it grow on limestone or granite?

Granite. One paper mentions limestone in its text, but its own table, the PACSOA profile and the 2019 Thai report all describe bare granite outcrops and cliffs in full sun.

How big does it get?

Large: the trunk can reach 10 m, the crown often carries more than 60 leaves up to 2.5 m long, and the male cones reach 60 cm.

Is it slow-growing?

Less so than many cycads, according to the available sources. PACSOA calls it vigorous and in Thailand it is promoted as the fastest-growing native cycad; no growth measurement has been published, however.

Is it endangered?

Yes. The IUCN has listed it as Critically Endangered since 2010, because of its tiny range and collecting. The 2023 survey nevertheless found more plants than expected, and the species is now widely propagated in Thai nurseries.

Can it be grown outdoors in the UK or the cooler parts of the US?

Nobody knows, and it seems unlikely. There is no measurement of cold tolerance and no outdoor trial outside Thailand; the prudent course is a pot kept frost-free under glass.

Is it poisonous?

It must be assumed so. There is no analysis for the species, but all the Cycas studied contain toxins dangerous to people and animals, especially in the seeds.

Further reading on Succulentes

Sources

Reference sites

Bibliography

  • Hill, K.D. & Yang, S.-L. (1999). The genus Cycas (Cycadaceae) in Thailand. Brittonia 51(1): 48–73. doi:10.2307/2666557 [Revision of the genus in Thailand, with the original description of Cycas chamaoensis on pages 58–60; reference checked through The World List of Cycads.]
  • Jutta, M., Chew, K.L. & Saw, L.G. (2010). A new species of Cycas (Cycadaceae) from Peninsular Malaysia. Blumea 55(3): 249–252. doi:10.3767/000651910X544438 [Comparative table of the closed-cone species: megasporophylls, seeds, habitat, section.]
  • Hill, K.D. (2010). Cycas chamaoensis. The IUCN Red List of Threatened Species 2010: e.T42037A10634719. doi:10.2305/IUCN.UK.2010-3.RLTS.T42037A10634719.en [First assessment, CR.]
  • Lindström, A. (2022). Cycas chamaoensis. The IUCN Red List of Threatened Species 2022: e.T42037A67339012. [Current assessment, CR A2ad; B1ab(i,ii,iv,v); C2a(i); D; taken from The World List of Cycads.]
  • Haynes, J.L. (2022). Etymological compendium of cycad names. Phytotaxa 550(1): 1–31. doi:10.11646/phytotaxa.550.1.1 [Etymology; cited by The World List of Cycads.]
  • Calonje, M., Stevenson, D.W. & Osborne, R. (2026). The World List of Cycads, version 2026.08.15. Montgomery Botanical Center, Coral Gables. doi:10.5281/zenodo.21958524 [Reference checklist.]