Cycas aculeata

Cycas aculeata is a cycad with an underground stem, endemic to central Vietnam and known from a single site on the southern slope of the Hai Van Pass, on the boundary between the city of Da Nang and Thua Thien-Hue province. Described in 2004, this species of the genus Cycas takes its name from the short but prominent spines on its petioles, and its young leaves emerge covered in orange down. The IUCN lists it as Endangered; it remains very poorly known and almost absent from collections.

Key facts about Cycas aculeata

  • Accepted name: Cycas aculeata K.D.Hill & T.H.Nguyên (2004), accepted by The World List of Cycads (version 2026.08.15); POWO could not be consulted directly
  • Former names and synonyms: none
  • Family: Cycadaceae, order Cycadales
  • Common names: no English common name attested; no vernacular name found in any other language
  • Natural range: central Vietnam, a single known site on the southern slope of the Hai Van Pass (Da Nang, on the boundary with Thua Thien-Hue)
  • IUCN status: Endangered (EN); latest assessment by J. D. Bösenberg and Nguyen Tien Hiep, published in Red List version 2023-1 (first assessment: Nguyen Tien Hiep, 2010)
  • CITES and other protection: CITES Appendix II (whole family; seeds exempt under annotation #4); Annex B in the European Union
  • Documented hardiness: no data (see Cold hardiness)
  • Light and soil: in the wild, deep loamy soil over granite according to the English Wikipedia; no cultivation data published
  • Habit and adult size: underground stem 15 to 18 cm across; 6 to 23 leaves 1.8 to 2.5 m long (figures from the English Wikipedia, see below)
  • In the UK, US and Australia: no botanic garden found in any of the three countries
  • Toxicity: no analysis specific to the species; treat it as poisonous, like all Cycas (see Toxicity and precautions)

How to recognise Cycas aculeata

Cycas aculeata is recognised by its stem hidden in the ground, its large, glossy, finely divided leaves and above all by its petiole armed with short, prominent spines, the feature that gave the species its name (Haynes 2022, as taken up by The World List of Cycads). The young leaves, covered in orange down, later turn dark green.

The original description (Hill, Nguyen and Loc 2004) is behind a paywall and could not be consulted. The following measurements come only from the English Wikipedia article, which relies on the Cycad Pages of the Royal Botanic Garden Sydney, written by K. D. Hill; they are given with that reservation.

  • Stem: short, underground or barely emerging, 15 to 18 cm across.
  • Leaves: 6 to 23 in the crown, pinnate, 1.8 to 2.5 m long, glossy dark green when mature, at first covered in orange down that soon disappears.
  • Petiole: armed with short, prominent spines.
  • Leaflets: 100 to 150 per leaf, 35 to 52 cm by 13 to 19 mm, with a single midrib as in all Cycas; the young leaves unroll like a crozier.
  • Male cones: single, 15 to 20 cm by 4 to 6 cm.
  • Female cones: not yet described.

Like all Cycas, the species is dioecious. That its female organs are still unknown some twenty years after its description says a great deal about how few observations exist.

Hybrids

No hybrid, natural or horticultural, is known. A species known from a single site and almost absent from collections has not been studied on this point.

Possible confusion

According to the English Wikipedia, its closest relative is Cycas balansae, a cycad of northern Vietnam and southern China that also has an underground stem and large leaves; no primary source consulted sets out the characters that separate them, apart from the very spiny petiole of Cycas aculeata. Without cones, and above all without female organs, which are still unknown, identifying a young plant is guesswork: a Vietnamese cycad without documented provenance should not be referred to this species on the strength of a spiny petiole alone.

The case has already arisen in Europe. In April 2014, a member of the French forum Fous de palmiers who had received some unnamed young Vietnamese cycads with underground stems listed Cycas aculeata among four possible identities, without being able to decide in the absence of cones.

Taxonomy

The World List of Cycads, the reference checklist of cycad specialists, accepts Cycas aculeata, which has no synonym. POWO could not be consulted directly; the International Plant Names Index (IPNI) records the name under the identifier 60436307-2.

The species was described in 2004 by the Australian botanist Kenneth D. Hill and the Vietnamese botanist Nguyen Tien Hiep, in the revision of the cycads of Vietnam co-written with Phan Ke Loc and published in The Botanical Review (volume 70, issue 2, pages 134 to 193); it is treated on pages 149 to 150, with a figure. The type (Nguyen and Hill 4156) was collected in 2000 low on the southern slope of the Hai Van Pass, in Phu Loc district (Thua Thien-Hue); the holotype is kept at the Hanoi herbarium (HN) and an isotype at Sydney (NSW). The collection date differs between databases: 23 January 2000 in The World List of Cycads, 23 June 2000 in IPNI.

Some sources place the species in section Stangerioides and mention a molecular signal linking it with Cycas siamensis, after a chapter by Hill (2004) on the classification of the Cycadaceae. That text could not be consulted and no other source gives the section of the species, so these statements are not repeated here.

Etymology and history

The epithet aculeata comes from the Latin aculeatus, “prickly”, “armed with prickles”, referring to the prominent spines of the petiole (Haynes 2022, as taken up by The World List of Cycads).

The history of the species is short. The type material was collected in 2000 by Nguyen Tien Hiep and Kenneth Hill, and the description appeared in September 2004 in the revision that made several new cycads of Vietnam known. No source documents its introduction into cultivation.

Common names

No common name is attested in English. The sources consulted give no Vietnamese or other vernacular name specific to the species either: only the scientific name is in use.

In the wild

Cycas aculeata is known from a single site, on the southern slope of the Hai Van Pass, the coastal pass that separates Da Nang from Thua Thien-Hue province in central Vietnam. The World List of Cycads places it in Da Nang, whereas the type label gives Phu Loc district in Thua Thien-Hue: both refer to the same slope, which straddles the boundary.

According to the English Wikipedia, it grows in deep loamy soil formed over granite. No published information was found on the exact altitude, the surrounding vegetation or the size of the population.

Conservation status and regulation

Cycas aculeata is listed as Endangered (EN) on the IUCN Red List. The first assessment, by Nguyen Tien Hiep, dates from 2010; a new assessment by J. D. Bösenberg and Nguyen Tien Hiep was published in Red List version 2023-1 (reference checked on Crossref), and EN is the category currently relayed from the IUCN by GBIF (consulted on 21 October 2026). The World List of Cycads gives the criteria A2acde and B1ab(i,ii,iii,v): a marked population decline in the recent past, observed or inferred from habitat loss, collecting and other factors, and a very small range limited to very few locations, with continuing decline in range, area occupied, habitat quality and number of adults. The IUCN pages could not be read (access blocked), so the precise threats are not detailed here.

Like all Cycas, the species is covered by CITES Appendix II, where the family Cycadaceae has been listed since 4 February 1977. Annotation #4 (CoP20 version, in force since 5 March 2026) exempts seeds, among other items; live plants, even young ones, still need permits in international trade. 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. Any plant offered for sale should therefore have a documented, cultivated origin. This general information was checked in October 2026 and does not replace the official texts: check the rules in force before buying or importing a plant.

Growing Cycas aculeata

In short: no growing experience has been published, and the species is exceptional in collections. What follows is deduced from its natural habitat, not from documented results.

Outdoor and in-ground cultivation

A plant from central Vietnam, growing in deep soil derived from granite, probably needs warmth, plenty of light or light shade and a deep but free-draining soil. Because its stem sits underground in contact with moist soil, good drainage is especially important to avoid rot. Watering can be regular during summer growth and sparser in the cool season. Outdoor planting can only be considered in frost-free tropical or subtropical climates, and no such trial has been reported.

Container cultivation

In the United Kingdom and other temperate regions, the cautious approach is a deep pot kept in a heated glasshouse or a bright conservatory, at least in winter, with a very free-draining compost. In Europe, no cultivation is documented: the only message on the French forum Fous de palmiers that mentions the species (2014) concerns unidentified seedlings. The Jardin zoologique tropical at La Londe-les-Maures, in the south of France, has published no observation on this species.

In cultivation in the UK, US and Australia

In short: no record found. The species does not appear in the online catalogues of the botanic gardens checked (Montgomery Botanical Center and Fairchild Tropical Botanic Garden in Florida, the Royal Botanic Garden Sydney, the Royal Botanic Gardens Victoria, Cambridge University Botanic Garden) or in the British, American and Australian lists of the BGCI PlantSearch database consulted in October 2026. No report from a private grower in these countries was found; PalmTalk and Dave’s Garden could not be consulted.

Propagation

Propagation is from seed. As the species is dioecious, a male and a female plant are needed and, in cultivation, hand pollination, all the more uncertain since the female cones have never been described. The fleshy coat of the seed is removed before sowing, wearing gloves; germination needs warmth and a free-draining compost kept just moist. Given the status of the species, look only for seed or plants of legal, documented origin.

Pests and diseases

No problem specific to the species has been published. In cultivation, the Asian cycad scale, Aulacaspis yasumatsui, which can kill an adult cycad within months, threatens cycads in general, but no attack has been reported on this species in particular. The main problem remains rot of the underground stem and roots, caused by overwatering or poor drainage.

Cold hardiness

No cold-tolerance data exist for Cycas aculeata. It lives under the tropical monsoon climate of central Vietnam, and nothing suggests that it can take frost.

European experience

No result of outdoor cultivation has been published in Europe, on the Mediterranean coast or elsewhere, and no dated frost episode concerns the species. On the French forum Fous de palmiers the name appears only once, as a possible identification, without growing data; the Italian forum Tropicamente does not mention it. Until there is evidence to the contrary, it is a plant for a warm glasshouse or a bright indoor position.

United Kingdom, United States and Australia

No cold measurement was found, either on growers’ forums or from botanic gardens. Treat the plant as frost-tender and keep it above freezing at all times; no USDA zone can be given without a documented trial.

Toxicity and precautions

No toxicity study specific to Cycas aculeata was found, but the risk is 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. In the absence of evidence to the contrary, treat this species 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. In any case, the seeds and tissues of cycads should never be eaten, and the status of the species rules out any collecting in the wild.

Frequently asked questions

What does the name aculeata mean?

“Prickly”. The epithet comes from the Latin aculeatus and refers to the short but prominent spines on the petioles of the leaves.

Where does Cycas aculeata grow?

At a single known site in central Vietnam: the southern slope of the Hai Van Pass, on the boundary between Da Nang and Thua Thien-Hue province.

How can it be recognised?

By its almost entirely underground stem, its spiny petiole and its young leaves covered in orange down. Without cones, however, a young plant cannot be identified with certainty.

Which species is it closest to?

To Cycas balansae, according to the English Wikipedia. Both species have an underground stem and large leaves; Cycas aculeata stands out mainly by its very spiny petiole.

Is it endangered?

Yes. The IUCN has listed it as Endangered since 2010, a category confirmed by the assessment published in 2023: it is known from a single site, with a declining population and habitat.

Can it be grown outdoors in the UK?

No. No cold-tolerance data exist and the species comes from a frost-free tropical climate; keep it under glass or indoors.

Is it available in the trade?

Almost never. The species is extremely rare in collections and is listed in CITES Appendix II: any plant offered should have a documented, cultivated origin.

Is it poisonous?

It must be assumed so. It has not been analysed, but the Cycas studied contain dangerous toxins, especially in the seeds.

Further reading on Succulentes

Sources

Reference sites

Bibliography

  • Hill, K.D., Nguyen, T.H. & Loc, P.K. (2004). The genus Cycas (Cycadaceae) in Vietnam. The Botanical Review 70(2): 134–193. doi:10.1663/0006-8101(2004)070[0134:TGCCIV]2.0.CO;2 [Original description of Cycas aculeata, pages 149–150, figure 2; reference checked on Crossref and IPNI, text not consulted (paywall).]
  • Nguyen, H.T. (2010). Cycas aculeata. The IUCN Red List of Threatened Species 2010: e.T42043A10636505. doi:10.2305/IUCN.UK.2010-3.RLTS.T42043A10636505.en [First assessment (EN); reference checked on Crossref, page not consulted (access blocked).]
  • Bösenberg, J.D. & Nguyen, T.H. (2023). Cycas aculeata. The IUCN Red List of Threatened Species 2023: e.T42043A67334346. doi:10.2305/IUCN.UK.2023-1.RLTS.T42043A67334346.en [Current assessment; reference checked on Crossref, EN category from GBIF, text not consulted (access blocked).]
  • Haynes, J.L. (2022). Etymological compendium of cycad names. Phytotaxa 550(1): 1–31. doi:10.11646/phytotaxa.550.1.1 [Etymology, as taken up by The World List of Cycads; not consulted directly.]
  • 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; consulted directly.]