Cycas inermis

Cycas inermis is a cycad of central and southern Vietnam, also recorded in central Laos, where it grows in the foothills. Described in the late eighteenth century by the Portuguese missionary and botanist João de Loureiro, it is one of the oldest names in the genus Cycas. Its epithet means “unarmed”, because Loureiro had always found his plant without spines. The name has had a troubled history: it was applied to other plants in Europe and China, reduced to a variety of the sago palm, and even declared illegitimate, before being restored for the Vietnamese species in 2004 and defended in 2009. The IUCN lists it as Vulnerable.

Key facts about Cycas inermis

  • Accepted name: Cycas inermis Lour. (Flora Cochinchinensis, dated 1790, published in 1793), accepted by The World List of Cycads (version 2026.08.15) and by GBIF; POWO could not be consulted directly
  • Former names and synonyms: Cycas revoluta var. inermis (Lour.) Miq. (1861); Cycas siamensis subsp. inermis (Lour.) J.Schust. (1932)
  • Family: Cycadaceae, order Cycadales
  • Common names: no English name attested; no vernacular name confirmed by a reliable source
  • Natural range: Vietnam (Da Nang, Quang Nam, Khanh Hoa and Dong Nai provinces) and Laos (Khammouane province)
  • IUCN status: Vulnerable (VU, criteria A2cd+4cd), assessment by John Donald Bösenberg published in 2022; category confirmed by the Red List data relayed by GBIF
  • CITES and other protection: CITES Appendix II (seeds exempt under annotation #4); Annex B in the European Union
  • Documented hardiness: no data (see Cold hardiness)
  • Light and soil: not documented in the sources consulted, beyond its occurrence in the foothills
  • Habit and adult size: not verified at source (the 2004 revision could not be read; see How to recognise)
  • In the UK, US and Australia: no garden record found
  • Toxicity: no data for the species; treat it as poisonous, like all Cycas (see Toxicity and precautions)

How to recognise Cycas inermis

No verified measurements can be given here. The reference description of the species is in Hill, Nguyen and Phan’s revision of the Cycas of Vietnam (The Botanical Review, 2004, pp. 182–186, figs 16 and 17), which is behind a paywall and could not be consulted. The descriptions and figures found elsewhere online could not be checked against it and have not been used.

The original description gives only a few characters. Loureiro states that his plant was always unarmed, that he never saw it branched, and that it was never monoecious; as Hill and Stanberg (2009) point out, he does not say which organs lacked spines. De Laubenfels and Adema (1998) add that Loureiro gave leaflets 15 cm long, whereas the Loureiro specimen kept at the Natural History Museum in London (BM) has leaflets 32 cm long.

The absence of spines is a poor guide on its own. In China, Metcalf gave the name Cycas inermis to another species, Cycas sexseminifera, whose petioles are often unarmed, a character that Hill (2008) describes as “not at all consistent”. Only a plant of documented wild origin, or a comparison with the 2004 description, allows a reliable identification.

Hybrids

No natural or cultivated hybrid is documented for this species.

Possible confusion

Because the name was applied to several different plants, the risk of confusion is above all a matter of labels and old literature:

  • Cycas macrocarpa, from Thailand and Peninsular Malaysia, its closest relative according to Hill and Stanberg (2009);
  • Cycas sexseminifera, a small cycad of Guangxi and northern Vietnam, to which Metcalf applied the name Cycas inermis in 1942 because its petioles are often spineless (Hill 2008);
  • Cycas revoluta, the sago palm: Miquel made Cycas inermis a variety of it in 1861 and had given the name to spineless plants grown in Amsterdam, which Hill (2008) identifies as aberrant Cycas revoluta; de Laubenfels and Adema (1998) later placed the name in its synonymy;
  • Cycas siamensis, the cycad of the Indochinese savannas, to which Schuster attached the plant as a subspecies in 1932;
  • Cycas riuminiana, from the Philippines, to which Hill and Stanberg (2009) refer the type of Cycas truncata, a name published by de Laubenfels in 2007 with Cycas inermis in its synonymy.

Taxonomy

Cycas inermis is a name accepted by The World List of Cycads and by GBIF; POWO could not be consulted directly. João de Loureiro published it in his Flora Cochinchinensis (volume 2, p. 632), a work dated 1790 but issued in October 1793 according to the reference work Taxonomic Literature, as cited by The World List of Cycads. A Loureiro specimen at the Natural History Museum in London (BM) can reasonably be taken as the holotype (Hill et al. 2004; Hill and Stanberg 2009).

The later history of the name is complicated. In 1861 Miquel reduced it to a variety of Cycas revoluta; as early as 1851 he had given it, wrongly, to plants grown at the Amsterdam botanic garden, brought from Bogor and said to come from southern China, which Hill (2008) identifies as aberrant Cycas revoluta without petiole spines. In 1932 Schuster attached it to Cycas siamensis as a subspecies, and in 1942 Metcalf applied it in China to the species now called Cycas sexseminifera. In their 1998 revision, de Laubenfels and Adema treated the name as illegitimate, on the grounds that Loureiro had given it as a synonym of Cycas revoluta; they matched his description to an undescribed cycad from Saraburi, in Thailand, while noting that the London specimen, if taken as the type, would belong to yet another of their species. In 2007 de Laubenfels went further and placed Cycas inermis in the synonymy of his new Cycas truncata, from the Philippines.

Hill and Stanberg (Telopea, 2009) rejected this reading. In the Latin text, Loureiro cites Cycas circinalis, Cycas revoluta and the “Olus Calapoides” of Rumphius in order to compare them with his plant: in his view those three did not deserve to be kept apart, but his own differed from them because he had always found it unarmed. The name is therefore validly and legitimately published, and it is Cycas truncata, published with Cycas inermis as a synonym, that becomes illegitimate. Hill, Nguyen and Phan (2004) had already applied the name to the species of the foothills of central and southern Vietnam, which Hill and Stanberg describe as widespread and most closely related to Cycas macrocarpa; Hill (2008) likewise treats it as a distinct species from southern Vietnam. For the reader, this means that “Cycas inermis” in older books and catalogues may refer to quite different plants.

Etymology and history

The epithet comes from the Latin inermis, “unarmed”, a reference to the absence of spines (Haynes 2022, as cited by The World List of Cycads). Loureiro studied the flora of Cochinchina, in what is now southern Vietnam. His comment, in the translation given by Hill and Stanberg (2009), reads: “granted that I have always found it unarmed, in which [feature] it disagrees with them. I have never seen it branching, nor monoecious.” No history of the species’ introduction into cultivation is documented.

Common names

No English common name is attested for this species. No vernacular name could be confirmed in a reliable source: the Vietnamese names that circulate online could not be checked against a Vietnamese flora.

In the wild

The World List of Cycads records Cycas inermis in the Vietnamese provinces of Da Nang, Quang Nam, Khanh Hoa and Dong Nai, and in Khammouane province in Laos. Hill and Stanberg (2009) describe it as a widespread taxon of the foothills of southern and central Vietnam. GBIF holds 71 records under this name (consulted on 21 October 2026), 46 of them from Vietnam; it also lists 11 records from China, where the name was long applied to Cycas sexseminifera (Hill 2008), so these deserve caution.

Its vegetation type, soils, pollinator, phenology and seed dispersers are not documented in the sources consulted.

Conservation status and regulation

Cycas inermis is listed as Vulnerable (VU) by the IUCN, under criteria A2cd+4cd: a past and projected reduction of the population linked to the decline of its habitat and to exploitation. The current assessment, by John Donald Bösenberg, was published in version 2022-1 of the Red List (reference checked on Crossref), and the Red List data relayed by GBIF confirm the category (consulted on 21 October 2026). An earlier assessment, by H.T. Nguyen, was published in 2010. The Red List itself could not be consulted, and the specific threats are not detailed in the sources read.

Like every species in the genus except Cycas beddomei, Cycas inermis is listed in CITES Appendix II, through the listing of the family Cycadaceae, 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 exempt, whereas international trade in the plants themselves requires an export permit. Australia, the United Kingdom and the United States 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 (searches of 3 and 12 October 2026). 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 origin and prefer plants raised from cultivated seed.

Growing Cycas inermis

In short: no growing advice specific to Cycas inermis has been published, and no grower’s report was found. Its native range, the tropical foothills of central and southern Vietnam, points to a plant for warm, frost-free conditions; this is a deduction from its range, not a growing result.

Outdoor and in-ground cultivation

No planting in the open ground is documented outside its range. Only frost-free tropical and near-tropical climates can be considered, and no garden in the United Kingdom, the United States or Australia is known to grow it (see below).

Container cultivation

In temperate climates it would need a heated glasshouse or a pot brought in for the winter; no container growing report has been found. Searches of the French forum Fous de palmiers and the Italian forum Tropicamente found no report on this cycad (the results for “inermis” concerned Zamia inermis and unrelated plants), and the Jardin zoologique tropical at La Londe-les-Maures, in the south of France, has published no observation on it.

In cultivation in the UK, US and Australia

No record of Cycas inermis was found in BGCI PlantSearch, in the online catalogue of Montgomery Botanical Center (Florida), or in the inventory of cycads in British, American and Australian gardens compiled for this site (searches of 19 and 21 October 2026). Plants labelled with this name in older collections may well belong to other species, given the history of the name. No report from an English-speaking grower could be read; PalmTalk and Dave’s Garden could not be consulted.

Propagation

The plant is dioecious: a male and a female plant are needed to obtain seed. No germination data specific to the species have been published. Seeds are exempt from CITES under annotation #4; ask for seed from cultivated plants of known origin.

Pests and diseases

No pest or disease specific to the species is documented. Cycad scales, including the Asian cycad scale, Aulacaspis yasumatsui, can affect all cultivated species.

Cold hardiness

No cold-tolerance data exist for Cycas inermis. Its range in central and southern Vietnam is tropical, and nothing allows us to say that it tolerates frost.

Mediterranean experience

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

United Kingdom, United States and Australia

No cold reading or dated growing report was found, either on forums or from botanic gardens. No USDA zone can be given. In the UK and in most of the United States and Australia outside the tropics, keep it frost-free under glass.

Toxicity and precautions

No toxicity analysis specific to Cycas inermis has been found. 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 specific to this species is documented in the sources consulted.

Frequently asked questions

What does inermis mean?

“Unarmed” in Latin. Loureiro chose it because he had always found his plant without spines, although he did not say which parts he meant.

Is the name Cycas inermis valid?

Yes. De Laubenfels and Adema considered it illegitimate in 1998, but Hill and Stanberg showed in 2009 that Loureiro had described a distinct species and had not treated it as a synonym of Cycas revoluta.

Is it a variety of Cycas revoluta?

No. Miquel classified it as such in 1861, but it is a distinct Vietnamese species, closest to Cycas macrocarpa. The spineless plants that Miquel called inermis in Amsterdam were, according to Hill (2008), aberrant sago palms.

Where does it grow?

In the foothills of central and southern Vietnam, from Da Nang to Dong Nai, and in Khammouane province in central Laos.

Is it endangered?

Yes. The IUCN lists it as Vulnerable, because of the decline of its habitat and of exploitation.

Is it hardy?

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

Is it poisonous?

It must be assumed so. No analysis exists for the species, but all the cycads studied contain serious toxins, especially in the seeds.

Further reading on Succulentes

Sources

Reference sites

Bibliography

  • Loureiro, J. de (1790 [1793]). Flora Cochinchinensis 2: 632. Lisbon. [Original description; not consulted directly (BHL inaccessible), Latin text quoted and translated by Hill and Stanberg (2009).]
  • Hill, K.D., Nguyen, H.T. & Phan, L.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 [Reference revision, description pp. 182–186; not consulted (paywall).]
  • Hill, K.D. & Stanberg, L.C. (2009). Notes on Cycas truncata de Laub. and related matters. Telopea 12(3): 447–450. doi:10.7751/telopea20095832 [Validity of the name, Latin text of the original description and its translation, relationship with Cycas macrocarpa, distribution; full text consulted.]
  • Hill, K.D. (2008). The genus Cycas (Cycadaceae) in China. Telopea 12(1): 71–118. doi:10.7751/telopea20085804 [Misapplications of the name by Miquel and Metcalf; full text consulted.]
  • Laubenfels, D.J. de & Adema, F. (1998). A taxonomic revision of the genera Cycas and Epicycas gen. nov. (Cycadaceae). Blumea 43(2): 351–400. [Treatment of the name as illegitimate, leaflet length in the original description and on the London specimen; full text consulted.]
  • Laubenfels, D.J. de (2007). Cycas truncata de Laub., a long-known but not validly named species. Encephalartos 92: 17. [Not consulted; cited after Hill and Stanberg (2009).]
  • Bösenberg, J.D. (2022). Cycas inermis. The IUCN Red List of Threatened Species 2022-1: e.T42055A68902862. doi:10.2305/IUCN.UK.2022-1.RLTS.T42055A68902862.en [Current assessment (VU); reference checked on Crossref, category relayed by GBIF; Red List page not consulted (access blocked).]
  • Nguyen, H.T. (2010). Cycas inermis. The IUCN Red List of Threatened Species 2010-3: e.T42055A10640187. doi:10.2305/IUCN.UK.2010-3.RLTS.T42055A10640187.en [Previous assessment; reference checked on Crossref, not consulted.]
  • 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 given 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.]