Cycas aenigma

Cycas aenigma is a cycad of the Philippines described in 2008 from plants grown in the city of Puerto Princesa, on the island of Palawan, whose origin was then unknown. That puzzle gave the species its name. This member of the genus Cycas is recognised by its green or cream male cones bristling with long spines and by its very long megasporophylls with fine, long teeth. The IUCN now lists it as Endangered (EN).

Key facts about Cycas aenigma

  • Accepted name: Cycas aenigma K.D.Hill & A.Lindstr. (2008), 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 name attested, in English or any other language
  • Natural range: Philippines, island of Palawan; described from plants cultivated in Puerto Princesa, wild origin not documented in the sources read (see In the wild)
  • IUCN status: Endangered (EN), criteria B1ab(iii,v); assessment by Agoo and Lindström published in Red List version 2023-1
  • 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
  • Habit and adult size: trunk 0.5 to 4 m tall and 20 to 25 cm across; leaves 2 to 2.9 m long
  • In the UK, US and Australia: no botanic garden found in any of the three countries
  • Toxicity: no toxicity data specific to the species; treat it as poisonous, like all Cycas (see Toxicity and precautions)

How to recognise Cycas aenigma

The authors distinguish Cycas aenigma from every other species of the region by its robust male cones, whose microsporophylls end in a strong, spreading spine, and by its open female cones with long megasporophylls, whose very drawn-out tip carries long, fine teeth. The description published by Lindström, Hill and Stanberg (2008) is as follows:

  • Trunk: tree-like, 0.5 to 4 m tall, 20 to 25 cm across at the narrowest point; bark thin and smooth, base slightly swollen.
  • Leaves: bright, very glossy green, 200 to 290 cm long, flat, with 300 to 380 leaflets, always ending in a pair of leaflets; hairless petiole 40 to 60 cm long, spiny along almost its whole length.
  • Median leaflets: 30 to 34 cm by 10 to 13 mm, inserted at 60 to 75°, spaced 10 to 12 mm apart, much narrowed at the base (2.5 to 3 mm), clearly paler beneath; margins flat or slightly recurved, not wavy.
  • Cataphylls (the scales protecting the growing point): narrowly triangular, soft, hairy, 7 to 10 cm long.
  • Male cones: egg-shaped, green or cream, about 34 cm by 16 cm; microsporophylls about 8 cm long, ending in a spreading spine of about 47 mm.
  • Megasporophylls (the fertile leaves of female plants): 36 to 40 cm long, with brown down that soon falls, carrying 4 to 6 ovules; lance-shaped blade 22 to 24 cm by 3.5 to 4 cm, deeply or shallowly comb-like, with 24 to 34 lateral spines of 16 to 25 mm; terminal spine 11 to 14 cm.
  • Seeds: not seen when the species was described.

Hybrids

No natural or garden hybrid is documented.

Possible confusion

The authors compare the strong, spreading spines of the microsporophylls with those of several geographically distant species, none of which combines them with a green male cone or with such drawn-out megasporophylls:

  • Cycas circinalis and the related species of southern India;
  • Cycas pranburiensis, from Thailand;
  • in the Philippines, Cycas riuminiana and Cycas lacrimans, which the key of Lindström and colleagues (2008) separates from Cycas aenigma by a sterile part of the megasporophyll shorter than 80 mm, against more than 20 cm in Cycas aenigma.

Taxonomy

Cycas aenigma is accepted by The World List of Cycads; POWO could not be consulted directly. The species was described in 2008 by Ken Hill and Anders Lindström in Telopea (volume 12, pages 130 to 132, figure 3), in a revision of the Cycas of the Philippines written with Leonie Stanberg that brought the number of species in the country to ten, five of them new. The authors placed it in section Cycas, subsection Cycas (seeds without a spongy layer, narrow megasporophyll blade), because of the shape of its microsporophylls, shared with Cycas circinalis and its Indian allies.

In 2012, Esperanza Maribel Agoo and Domingo Madulid (Blumea, description of Cycas sancti-lasallei) included it in their key to the Philippine species, recalling that it was known only in cultivation; their key separates it by its leaves of 220 to 300 cm and its lance-shaped megasporophyll blade.

Etymology and history

The epithet comes from the Latin aenigma, “to speak in riddles”, the root of the English word “enigma”: something that cannot be satisfactorily explained. The authors chose it because this very distinctive species was known only as a cultivated plant (original description, as taken up by Haynes 2022).

The plants were recognised as new only in 2001, in cultivation in the city of Puerto Princesa. The type (no. 1617, a male plant) and a second collection (no. 1618, a female plant) were made there by Fernando on 26 June 2001; the holotype is kept at the Los Baños herbarium (LBC). The illustrations in the original description were drawn from Ken Hill’s slides.

Common names

No common name is attested for this species, in English or in any language of the Philippines, in the sources consulted.

In the wild

In 2008 the range and habitat of Cycas aenigma were unknown: the species was known only in cultivation in Puerto Princesa, and the authors considered it “probable”, without being able to confirm it, that the plants came from the island of Palawan. Agoo and Madulid still described it as known only in cultivation in 2012. The World List of Cycads now gives its range as “Philippines (Palawan, cultivated)”.

The IUCN listing under criterion B1, which concerns the extent of the natural range, suggests that wild populations have since been located. A search-engine snippet mentions three small wild populations on ultramafic soils on Palawan, but no verifiable publication was found to confirm this: the natural habitat therefore remains undocumented here.

Conservation status and regulation

Cycas aenigma is listed as Endangered (EN) under criteria B1ab(iii,v), a small range with declining habitat quality and number of mature individuals, according to The World List of Cycads. The assessment, by Esperanza Maribel Agoo and Anders Lindström, was published in Red List version 2023-1 (reference checked on Crossref); the IUCN data relayed by GBIF confirm the EN category (consulted on 21 October 2026). In 2008, for lack of data, the authors of the description recommended the category Data Deficient (DD). The Red List itself could not be consulted directly.

In 2008, Lindström and colleagues identified two main threats to Philippine cycads: habitat destruction and the collection of plants from the wild for trade or local use.

Like every species in the genus except Cycas beddomei, Cycas aenigma 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 aenigma

In short: by its very history Cycas aenigma is a garden plant, since it was discovered in gardens in Puerto Princesa, but no growing advice has been published.

Outdoor and in-ground cultivation

The only documented cultivation is that of the gardens of Puerto Princesa, on a tropical island, where the type plants were collected. Outdoors, the species can only be considered in frost-free tropical climates; no trial elsewhere has been published.

Container cultivation

In the United Kingdom and other temperate regions, its tropical origin makes it a plant for a heated glasshouse. No growing trial has been published in Europe, and 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

The plant is dioecious: a male and a female plant are needed for seed. Seeds had not been seen when the species was described, and no germination data have been published. Seeds are exempt from CITES under annotation #4; ask for seed from cultivated plants.

Pests and diseases

No pest specific to the species is documented. In the Philippines, Lindström and colleagues reported in 2008 that the Asian cycad scale, Aulacaspis yasumatsui, was devastating many cultivated cycads on Luzon, Negros and Panay; on Palawan it then seemed to be kept in check by natural predators in the wild populations of Cycas curranii and Cycas saxatilis.

Cold hardiness

No cold-tolerance data exist for Cycas aenigma. Palawan is a tropical island, and nothing suggests that the plant can take frost.

European experience

No cultivation result has been published in Europe, in the open ground or in a pot. A search of the French forum Fous de palmiers and the Italian forum Tropicamente found no report of cold tolerance for this species, and no dated frost episode concerns it. The Mediterranean experience available for other cycads therefore offers no guide here: it is a plant for a warm glasshouse.

United Kingdom, United States and Australia

No cold reading and no dated growing report were found. Treat the plant as frost-tender and keep it warm all year; no USDA zone can be given without a documented trial.

Toxicity and precautions

No toxicity analysis specific to Cycas aenigma was 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. A chemical study published in 2015 (Ng, Agoo, Shen and Ragasa, Journal of Applied Pharmaceutical Science) deals with the constituents of Cycas aenigma, but its content could not be consulted. In the absence of evidence to the contrary, 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.

Frequently asked questions

Why is it called aenigma?

Because it was known only as a cultivated plant in Puerto Princesa, with no known origin: aenigma means “riddle” in Latin.

Where does it come from?

From the Philippines. In 2008 the authors considered it probable that it came from the island of Palawan; no publication consulted describes its wild populations.

How can it be recognised?

By its green or cream male cones with long, spreading spines, and by its megasporophylls, 36 to 40 cm long, whose drawn-out tip carries long, fine teeth.

Is it endangered?

Yes. The IUCN lists it as Endangered (EN); in 2008, for lack of data, Data Deficient was recommended.

Can it be grown?

Yes, in a heated glasshouse. It was discovered in cultivation, but no growing advice has been published.

Can it be grown outdoors in the UK?

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

Is it poisonous?

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

Further reading on Succulentes

Sources

Reference sites

Bibliography

  • 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 [Original description (pp. 130–132), key, threats, Aulacaspis; full text consulted.]
  • Agoo, E.M.G. & Madulid, D.A. (2012). Cycas sancti-lasallei (Cycadaceae), a new species from the Philippines. Blumea 57: 131–133. doi:10.3767/000651912X657503 [Key to the Philippine species; “known only in cultivation”; full text consulted.]
  • Ng, V.A.S., Agoo, E.M.G., Shen, C.-C. & Ragasa, C.Y. (2015). Chemical constituents of Cycas aenigma. Journal of Applied Pharmaceutical Science 5(9): 32–36. doi:10.7324/JAPS.2015.50906 [Reference checked on Crossref; content not consulted.]
  • Agoo, E.M.G. & Lindström, A. (2023). Cycas aenigma. The IUCN Red List of Threatened Species 2023: e.T187353A1826898. doi:10.2305/IUCN.UK.2023-1.RLTS.T187353A1826898.en [Red List assessment; reference checked on Crossref, category confirmed by GBIF and The World List of Cycads; page 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 [Source of the etymologies 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.]