Cycas pranburiensis

Cycas pranburiensis is a small cycad of the limestone hills of Prachuap Khiri Khan province, in south-western Thailand, where it clings to cliffs and rocky slopes around Khao Sam Roi Yot National Park. This species of the genus Cycas was described in 1999 by S.L. Yang, W. Tang, K.D. Hill and P. Vatcharakorn, and named after the district of Pran Buri. It branches from an early age, sometimes carrying as many as twenty crowns. The IUCN lists it as Critically Endangered.

Key facts about Cycas pranburiensis

  • Accepted name: Cycas pranburiensis S.L.Yang, W.Tang, K.D.Hill & Vatch. (1999), accepted by The World List of Cycads (version 2026.08.15) and by GBIF; 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: no synonym; the plants of Sam Roi Yot were previously included in Cycas circinalis by Smitinand (1971)
  • Family: Cycadaceae, order Cycadales
  • Common names: no English name attested; in Thai, prong khao sam roi yot (ปรงเขาสามร้อยยอด) and prong pran buri (ปรงปราณบุรี); “Pranburi sago” is a nursery name
  • Natural range: Thailand, Prachuap Khiri Khan province (Pran Buri district, Khao Sam Roi Yot National Park)
  • IUCN status: Critically Endangered (CR, criterion B1ab(v)), assessment by K.D. Hill (2010), reassessed by J.D. Bösenberg in Red List version 2023-1; CR according to GBIF; Vulnerable on the Thai national red list
  • CITES and other protection: CITES Appendix II (seeds exempt under annotation #4); Annex B in the European Union; export not permitted by Thailand
  • Documented hardiness: no data (see Cold hardiness)
  • Light and soil: in the wild, cliffs, steep slopes and rock crevices in limestone, between about 10 and 100 m; no cultivation data
  • Habit and adult size: small cycad with erect, decumbent or hanging stems, often branched; measured dimensions not available
  • In the UK, US and Australia: declared by San Diego Botanic Garden (California) and the University of Hawaii at Hilo botanical garden; no record in the United Kingdom or Australia
  • Toxicity: no data specific to the species; treat it as poisonous, like all Cycas (see Toxicity and precautions)

How to recognise Cycas pranburiensis

Cycas pranburiensis is a small rock-dwelling cycad that branches early and forms clumps of several crowns. Its microsporophylls end in a stout, spreading apical spine, comparable to that of Cycas circinalis and its relatives in peninsular India (Lindström et al. 2008). The original description (Yang et al. 1999) and the treatment by Hill and Yang (1999) could not be read: the description below comes from a 2019 report by Thailand’s Department of Agriculture, translated from Thai, and gives no measurements.

  • Trunk: bark almost smooth and yellowish; stems erect, decumbent or hanging, branching and producing small offsets along the trunk; some plants carry up to twenty crowns.
  • Leaves: pinnate, erect then spreading, with numerous, crowded, regular, leathery-looking leaflets; the rachis does not end in a spine, and the lower leaflets are not reduced to spines; the midrib is raised on both surfaces.
  • Cataphylls (the scale leaves that protect the growing point): triangular and soft, with short light brown to grey down.
  • Male cones: ovoid and orange, with a very strong, unpleasant smell; each microsporophyll ends in a spine.
  • Female cone: narrowly conical; the megasporophylls, covered in grey felt-like down, hang down as the seeds swell, and their short tip bears lateral spines.
  • Seeds: ovoid, with an orange coat containing a fibrous layer and no spongy layer. According to the same report, the plant produces very few seeds, 50 to 200 per coning.

Hybrids

No hybrid is documented for this species.

Possible confusion

In Thailand, several limestone-dwelling cycads are each confined to one massif: Cycas tansachana (Saraburi), Cycas petraea (Loei and Khon Kaen) and Cycas clivicola (cliffs of the south). The characters that separate them from Cycas pranburiensis are not given. On the French forum Fous de palmiers, a collector listed Cycas pranburiensis in January 2010 among the possible names for a misidentified Thai cycad, which shows how hard these plants are to name without cones.

Cycas aenigma, from the Philippines, has equally stout and spreading microsporophyll spines, but a green male cone and very long-tapering megasporophylls (Lindström et al. 2008). Before the species was described, the Sam Roi Yot plants were filed under Cycas circinalis: Smitinand (1971) cites under that name the collection that later became the type of Cycas pranburiensis.

Taxonomy

Cycas pranburiensis is a name accepted by The World List of Cycads and by GBIF; the World Checklist of Vascular Plants (WCVP), on which POWO is based, also accepts it (consulted through GBIF on 31 October 2026). The species was described in 1999 by S.L. Yang, W. Tang, K.D. Hill and P. Vatcharakorn in Brittonia (51(1): 44–47, fig. 1), in the same issue as Hill and Yang’s revision of the Cycas of Thailand (pp. 48–73), which describes it on pages 68 and 69.

Lindström et al. (2008) place it in subsection Cycas of section Cycas, with Cycas circinalis and its Indian allies, because of the shape of its microsporophylls. The phylogenetic analysis by Liu and colleagues (2018), carried out at the Kunming Institute of Botany, places Cycas pranburiensis and Cycas macrocarpa instead in the lineage of section Indosinenses: the position of the species within the genus therefore remains open.

Etymology and history

The epithet refers to its endemic occurrence in Pran Buri district, in the north of Prachuap Khiri Khan province (Haynes 2022).

The type is a much older collection: specimen Kerr 10972, gathered at Sam Roi Yot on 13 July 1926; the holotype is at Kew (K), with isotypes in Bangkok (BK) and at the Natural History Museum in London (BM), according to The World List of Cycads. In his 1971 account of the Thai Cycas, Tem Smitinand of the Royal Forest Department cited this specimen (“Sam Roi Yot, under 50 m”) under Cycas circinalis. In 2004, W. Tang, one of the authors, devoted an article in the journal Encephalartos to the species (“Focus on Cycas pranburiensis”). No history of its introduction into cultivation is documented.

Common names

No English common name is attested; the British nursery Trebrown uses “Pranburi sago”, a commercial name built from the epithet. In Thai, the Department of Agriculture calls it ปรงเขาสามร้อยยอด (prong khao sam roi yot, “cycad of Khao Sam Roi Yot”), after the national park where it grows, while the biodiversity information system of the Thai Office of Natural Resources and Environmental Policy and Planning (ONEP) uses ปรงปราณบุรี (prong pran buri, “cycad of Pran Buri”); prong is the Thai name for cycads.

In the wild

Cycas pranburiensis grows only on the limestone hills of Prachuap Khiri Khan province. According to Thailand’s Department of Agriculture, it occurs on cliffs, steep mountainsides and the slopes of the limestone massifs of Khao Sam Roi Yot National Park, often in their lower parts, in thorny scrub forest, in crevices and between sharp-edged blocks of rock. ONEP gives an altitude of about 10 to 100 m, and Smitinand (1971) recorded the 1926 collection at “under 50 m”. The ONEP database also mentions southern Vietnam, a record that neither The World List of Cycads nor the Thai authors repeat and that remains to be verified.

Pollination and phenology are not documented.

Conservation status and regulation

The IUCN lists Cycas pranburiensis as Critically Endangered (CR) under criterion B1ab(v) in the assessment by K.D. Hill (2010) cited by The World List of Cycads: its range is tiny and the number of mature plants is declining. A reassessment by J.D. Bösenberg was published in version 2023-1 of the Red List (reference found on Crossref); the Red List data relayed by GBIF give the category as CR (consulted on 24 October 2026), but these data do not give the criteria of the new assessment. At national level, the Thai plant red list (ONEP 2006) and the Department of Agriculture report (2019) place it in the Vulnerable category.

That report, prepared for the CITES non-detriment findings, notes that all Thai cycad species suffer from illegal removal of whole plants and offsets, and recommends that no species be authorised for export except Cycas chamaoensis and Cycas siamensis, for lack of sufficient artificial propagation.

Like every species in the genus except Cycas beddomei, Cycas pranburiensis is listed in CITES Appendix II, where the family Cycadaceae has been included since 4 February 1977. The listing carries annotation #4 (CoP20 version, in force since 5 March 2026): seeds, pollen, seedlings or tissue cultures obtained in vitro and transported in sterile containers, and cut flowers of artificially propagated plants, are not subject to CITES, whereas international trade in the plants themselves requires 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+, the official CITES database, names the species and confirms this status.

This general information does not replace the official texts: check the rules in force before buying or exchanging plants, ask the seller for proof of provenance and prefer plants raised from seed in cultivation.

Growing Cycas pranburiensis

In short: no institution documents its cultivation and no grower’s report is documented, in English, French or Italian. It is a plant of tropical limestone outcrops with a dry season, and any advice is a deduction from its habitat.

Outdoor and in-ground cultivation

Outdoors, it can only be considered in a tropical climate without a cold season. Its habitat, crevices and rocky slopes of lowland limestone, points to a very free-draining, mineral substrate and to a site that dries out quickly after rain; no source confirms this, and no outdoor trial has been published anywhere.

Container cultivation

In the United Kingdom and other temperate regions, it would be a plant for a heated glasshouse, in a pot. No Mediterranean experience is available either: the French forum Fous de palmiers mentions it only in an identification discussion.

In cultivation in the UK, US and Australia

In short: very rare in collections.

  • United States: San Diego Botanic Garden (Encinitas, California) and the botanical garden of the University of Hawaii at Hilo declare the species in the BGCI PlantSearch database (consulted on 24 October 2026). It does not appear in the online catalogue of Montgomery Botanical Center.
  • Australia and United Kingdom: no garden declares it in BGCI, and no other record is documented.

Outside these three countries, BGCI also lists Prague Botanical Garden and Singapore Botanic Gardens. A BGCI entry shows that a garden has declared the species at some point, not that a plant is alive there today.

Propagation

Like all Cycas, Cycas pranburiensis is dioecious: a male and a female plant are needed for fertile seed, which it produces in small numbers. The offsets it forms along the trunk could be used to propagate it; the Thai report recommends, for cycads in general, sowing, the separation of offsets and reintroduction. No germination data specific to the species have been published. Seeds are exempt from CITES under annotation #4; given the export ban, only seed or plants raised in cultivation, with documents, should be sought.

Pests and diseases

No pest or disease specific to the species is documented. In cultivation, scale insects, including Aulacaspis yasumatsui, can attack any Cycas.

Cold hardiness

No cold-tolerance data exist for Cycas pranburiensis. It grows at low altitude in a frost-free tropical region, and nothing suggests that it can take frost.

Mediterranean and European experience

No cultivation result has been published in Europe, in the open ground or in a pot, and no dated frost episode concerns the species.

United Kingdom, United States and Australia

No cold reading and no dated growing report are documented, either on forums or from botanic gardens. The British nursery Trebrown rates it USDA zone 9b (average annual minimum of −3.9 to −1.1 °C, or 25 to 30 °F), a commercial rating not backed by any published growing observation.

Toxicity and precautions

No toxicity analysis specific to Cycas pranburiensis has been published. The risk is, however, well documented in the genus: Cycas tissues, and the seeds above all, 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) as poisonous to dogs, cats and horses. Until proven otherwise, treat the plant as poisonous: keep seeds and leaves out of reach of children and pets, and wear gloves to clean the seeds. If any part is swallowed, contact a poison centre, a doctor or a vet straight away.

Traditional uses

No use is documented for this species; the removals reported in Thailand supply the ornamental plant trade.

Frequently asked questions

Where does the name pranburiensis come from?

From Pran Buri district, in Prachuap Khiri Khan province, Thailand, where the species grows.

Where does Cycas pranburiensis grow?

Only on the limestone hills of Prachuap Khiri Khan province, around Khao Sam Roi Yot National Park, on cliffs and in rock crevices at low altitude.

How can it be recognised?

It is a small rock-dwelling cycad that branches early, sometimes into some twenty crowns, with orange, strong-smelling male cones and microsporophylls ending in a stout spine.

Was it once called Cycas circinalis?

Yes, in a sense. Before 1999 the Sam Roi Yot plants were filed under Cycas circinalis, a name now restricted to a species of southern India; the type specimen, collected in 1926, was cited under that name by Smitinand in 1971.

Is it endangered?

Yes. The IUCN lists it as Critically Endangered, and Thai cycads suffer from illegal collecting.

Can it be bought?

Thailand does not permit its export. Any plant offered should come from seed raised in cultivation, with documents to prove it.

Is it hardy?

Almost certainly not. No cold data exist; it is a tropical lowland plant.

Is it poisonous?

It must be assumed so. No toxicity analysis specific to the species exists, but the Cycas studied contain dangerous toxins, especially in the seeds.

Further reading on Succulentes

Sources

Reference sites

Bibliography

  • Yang, S.-L., Tang, W., Hill, K.D. & Vatcharakorn, P. (1999). Cycas pranburiensis (Cycadaceae), a new cycad from Thailand. Brittonia 51(1): 44–47. doi:10.2307/2666555 [Original description.]
  • Hill, K.D. & Yang, S.-L. (1999). The genus Cycas (Cycadaceae) in Thailand. Brittonia 51(1): 48–73. [Description on pp. 68–69.]
  • Smitinand, T. (1971). The genus Cycas Linn. (Cycadaceae) in Thailand. Natural History Bulletin of the Siam Society 24: 163–175. https://thesiamsociety.org/wp-content/uploads/2020/04/NHBSS_024_1-2k_Smitinand_TheGenusCycasLi.pdf [Kerr 10972 (Sam Roi Yot, under 50 m) cited under Cycas circinalis.]
  • Tang, W. (2004). Focus on Cycas pranburiensis. Encephalartos 80: 15–22. [Reference taken from The World List of Cycads.]
  • Lindström, A.J., Hill, K.D. & Stanberg, L.C. (2008). The genus Cycas (Cycadaceae) in the Philippines. Telopea 12(1): 119–145. doi:10.7751/telopea20085805 [Comparison of microsporophylls and placement in subsection Cycas.]
  • Liu, J., Zhang, S., Nagalingum, N.S., Chiang, Y.-C., Lindstrom, A.J. & Gong, X. (2018). Phylogeny of the gymnosperm genus Cycas L. (Cycadaceae) as inferred from plastid and nuclear loci based on a large-scale sampling: evolutionary relationships and taxonomical implications. Molecular Phylogenetics and Evolution 127: 87–97. [Phylogenetic position; summarised on the genus page of this site.]
  • Hill, K.D. (2010). Cycas pranburiensis. The IUCN Red List of Threatened Species 2010: e.T42063A10641032. doi:10.2305/IUCN.UK.2010-3.RLTS.T42063A10641032.en [Assessment cited by The World List of Cycads.]
  • Bösenberg, J.D. (2023). Cycas pranburiensis. The IUCN Red List of Threatened Species: e.T42063A69155175. doi:10.2305/IUCN.UK.2023-1.RLTS.T42063A69155175.en [Reassessment; reference found on Crossref, CR category relayed by GBIF.]
  • Haynes, J.L. (2022). Etymological compendium of cycad names. Phytotaxa 550(1): 1–31. doi:10.11646/phytotaxa.550.1.1 [Source of the etymologies taken up 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.]