Cycas glauca

Cycas glauca is a cycad of the eastern Lesser Sunda Islands, known from Timor (Indonesian West Timor and Timor-Leste) and from the island of Sumba, where it grows in inland evergreen forest, often near streams. Described as early as 1840 by the Dutch botanist Friedrich Anton Wilhelm Miquel from plants grown in Europe, this member of the genus Cycas owes its name to the waxy blue sheen of its leaves. It remained a puzzle for more than a century and a half, filed in turn under Cycas circinalis, Cycas rumphii and Cycas thouarsii, and was only clearly understood in 2009. The IUCN now lists it as Critically Endangered.

Key facts about Cycas glauca

  • Accepted name: Cycas glauca Hort. ex Miq. (1840), accepted by The World List of Cycads (version 2026.08.15); POWO could not be consulted directly
  • Former names and synonyms: Cycas rumphii var. timorensis Miq. (1840); Cycas circinalis f. glauca (Miq.) J.Schust. (1932); plants formerly referred to Cycas rumphii and Cycas thouarsii
  • Family: Cycadaceae, order Cycadales
  • Common names: no English name; “fay” in the Amarassi dialect of West Timor
  • Natural range: Indonesia (East Nusa Tenggara: West Timor and Sumba) and Timor-Leste
  • IUCN status: Critically Endangered (CR, criteria A2ac+4ace according to The World List of Cycads), in the reassessment by Anders Lindström published in 2023; 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: closed or more open inland evergreen forest, often near streams, on clay; persists in disturbed habitats
  • Habit and adult size: trunk up to 3 m tall and 22 to 35 cm across, sometimes branched at the top; leaves 174 to 220 cm long
  • In the UK, US and Australia: no garden record found under this name
  • Toxicity: no data for the species; treat it as poisonous, like all Cycas (see Toxicity and precautions)

How to recognise Cycas glauca

Cycas glauca is recognised by the clearly visible blue-glaucous sheen on its dark green leaves, especially as they emerge, by its broad leaflets (12 to 16 mm) and by its heavily bloomed seeds, which have no spongy layer. Its megasporophylls (the fertile leaves of female plants) have a small, barely comb-like blade ending in a distinct spine. Description after Lindström, Hill and Stanberg (2009):

  • Trunk: upright, up to 3 m tall and 22 to 35 cm across, usually single but sometimes branching two to four times at the top.
  • Leaves: 174 to 220 cm long, dark semi-glossy green with a blue-glaucous sheen, flat, with 69 to 118 leaflets; some down often remains even on mature leaves; petiole 42 to 58 cm (20 to 40% of the leaf), with short orange down, bloomed, spiny over 20 to 100% of its length.
  • Median leaflets: 15 to 30 cm long and 12 to 16 mm wide, hairless, slightly paler below, 5 to 14 mm apart; margins recurved; midrib slightly raised above, strongly raised below.
  • Cataphylls (the scale leaves protecting the crown): narrow, elongated, soft, 3 to 4 cm long.
  • Male cones: about 49 cm long and 10 cm across, brownish, on an 8 cm stalk; microsporophylls 38 to 40 mm by 18 to 20 mm, with an upturned apical spine up to 20 mm long.
  • Megasporophylls: 30 to 43 cm long, with persistent orange-brown down, carrying 4 to 7 hairless ovules; blade 25 to 40 mm by 23 to 35 mm, shortly comb-like or with rudimentary spines; distinct apical spine 20 to 40 mm long.
  • Seeds: flattened, 4 to 5 cm long and up to 3 cm wide; fleshy coat yellow, then dark reddish brown, heavily bloomed, without a fibrous layer; inner shell weakly sculptured; no spongy layer.

Hybrids

No natural or cultivated hybrid is documented for this species.

Possible confusion

  • Cycas rumphii, a coastal cycad of eastern Indonesia with which it has been confused: leaves without a blue sheen, seeds with a spongy layer that makes them float.
  • Cycas thouarsii, of the western Indian Ocean (Madagascar, the Comoros, East Africa), which it resembles in its bluish leaves: narrower leaflets and larger seeds with a spongy layer.
  • Cycas sundaica, from the neighbouring islands of Sumbawa, Flores and Alor: megasporophylls with clear lateral spines, seeds with a spongy layer.
  • Cycas silvestris, from Queensland, its probable closest relative judging by the width of the leaflets: no blue sheen on the young leaves.

Taxonomy

Cycas glauca is a name accepted by The World List of Cycads; POWO could not be consulted directly. The name “glauca” was circulating in European gardens before Miquel published it in his Commentarii Phytographici (1840–1841, page 127), hence the author citation “Hort. ex Miq.”; Link (1821–1822) and Sweet (1839) had used it without a description (nomina nuda). In the same work Miquel also described Cycas rumphii var. timorensis, from a Timor specimen in the Paris Museum, now a synonym.

The types of both names consist only of sterile leaves, which made them very hard to match with any known species. Miquel himself later listed Cycas glauca among the doubtful species (1861, 1868), as did Lemaire (1864) and de Candolle (1868); Regel kept it in 1876, and in 1932 Julius Schuster made it a form of Cycas circinalis. Ken Hill first placed it in the synonymy of Cycas rumphii (1995), then in that of Cycas thouarsii (1998). De Laubenfels and Adema (1998), unaware of the Utrecht specimen, treated it as a nomen nudum, placed it under Cycas rumphii (page 369) and attached the variety timorensis to their new Cycas edentata.

Field surveys on Sumba and Timor in 2000 showed that it is a distinct species, unrelated to the Cycas rumphii group. Lindström, Hill and Stanberg (Telopea, 2009) then designated as lectotype a herbarium sheet in Utrecht from the Rotterdam garden, and placed the species in subsection Endemicae of section Cycas, a mainly Australian group of which it is the only species known outside Australia and New Guinea. For the reader, this means that older books and labels may call this plant Cycas rumphii, Cycas circinalis or Cycas thouarsii.

Etymology and history

The epithet comes from the Greek glaukos, Latinised as glaucus, “blue-green, covered with a bluish bloom”, a reference to the glaucous leaves (Lindström et al. 2009; Haynes 2022). The species is a rare case of a cycad described from European garden plants more than a century and a half before its wild populations were studied: its type comes from the Rotterdam garden, which shows that it was already grown in Europe in the nineteenth century.

Common names

No English common name specific to the species was found in the sources consulted, and none is attested in French. Lindström and colleagues (2009) record the name “fay” in the Amarassi dialect of West Timor.

In the wild

Cycas glauca is known from Timor and Sumba, in the Lesser Sunda Islands. In West Timor it has been collected in Kupang regency, near the villages of Oekabiti and Baun (about 415 m), in the Amarassi area; on Sumba near Paimburu (about 274 m), in the north of West Sumba, and in cultivation at Waingapu. The World List of Cycads also records it in Timor-Leste, with photographs of observations made in 2023 in Covalima municipality and in 2003 in Lautém municipality. GBIF holds 41 records under this name (consulted on 21 October 2026), including 16 iNaturalist observations from Covalima in 2023.

It grows in inland evergreen forest, closed or more open and seasonally dry, often near streams, on clay soil, and persists in disturbed habitats. In 2009 it appeared fairly widespread and locally abundant on both islands. Its pollinator and seed dispersers are not documented.

Conservation status and regulation

Cycas glauca is listed as Critically Endangered (CR) by the IUCN, under criteria A2ac+4ace according to The World List of Cycads: an observed and projected population reduction, linked to the decline of its habitat and to exploitation. Two assessments are on record: one by John Donald Bösenberg (2010) and the reassessment by Anders Lindström, published in version 2023-1 of the Red List (reference checked on Crossref). The current category, relayed by GBIF from the IUCN data (consulted on 21 October 2026), is CR, which is therefore that of the 2023 reassessment. The Red List itself could not be consulted, and the category given in 2010 could not be checked. In 2009 Lindström and colleagues recommended Vulnerable, while noting that it was not known whether any populations lay within protected areas and that political instability complicated any protective measure.

They also reported that the Asian cycad scale, Aulacaspis yasumatsui, had been introduced to Timor and had become established in West Timor, but had not then been found outside the capital, Kupang.

Like every species in the genus except Cycas beddomei, Cycas glauca 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, with Indonesia and Timor-Leste as range states, 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 glauca

In short: although the species has been in cultivation since the nineteenth century, no growing advice specific to it has been published, and no grower’s report was found.

Outdoor and in-ground cultivation

Lindström and colleagues (2009) studied male cones on plants growing at Nong Nooch Tropical Garden in Thailand, and the species is also cultivated at Waingapu, on Sumba. These are tropical settings. In the wild it grows on clay in forest that is partly seasonally dry; this suggests a warm, frost-free climate, a deduction from its habitat rather than a growing result.

Container cultivation

In temperate climates it would have to be grown in a heated glasshouse; 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 species, 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 garden declares Cycas glauca in BGCI PlantSearch, and the inventory of cycads in British, American and Australian gardens compiled for this site found no plant under this name (searches of 19 and 21 October 2026). The online catalogue of Montgomery Botanical Center (Florida) lists no accession as Cycas glauca, but its record for Cycas thouarsii carries the note “Accepted name: Cycas glauca”, a remark that contradicts the displayed name and must be read with caution; what it means for these plants could not be checked. Because the species was long filed under Cycas rumphii, Cycas circinalis and Cycas thouarsii, old garden plants may still carry one of those names; no source consulted identifies such a plant. 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.

Pests and diseases

No disease specific to the species is documented. The Asian cycad scale, Aulacaspis yasumatsui, introduced to Timor, is the main pest threat reported within its range: it once destroyed the entire cycad collection of the Bogor Botanic Garden, on Java (Lindström et al. 2009).

Cold hardiness

No cold-tolerance data exist for Cycas glauca. Timor and Sumba are tropical islands, and the collections cited by Lindström and colleagues (2009) come from low and middle altitudes (up to about 415 m); nothing allows us to say that the plant 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. Searches of the French forum Fous de palmiers and the Italian forum Tropicamente found no cold report.

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 glauca 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 is documented for this species in the sources consulted; the Amarassi name “fay” shows only that the plant is known to the people of West Timor.

Frequently asked questions

What does glauca mean?

“Blue-green, bloomed”: the name describes the waxy blue sheen of the leaves.

Where does Cycas glauca grow?

On Timor (both the Indonesian side and Timor-Leste) and on the island of Sumba, in inland evergreen forest, often near streams.

Is it a form of Cycas rumphii or Cycas circinalis?

No. It was filed under both, then under Cycas thouarsii, but the study of its wild populations showed in 2009 that it is a distinct species, related to the Australian cycads.

How can it be told from Cycas thouarsii?

By its broader leaflets and its smaller seeds, which have no spongy layer; Cycas thouarsii lives in the western Indian Ocean.

Is it endangered?

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

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

  • Miquel, F.A.W. (1840–1841). Commentarii Phytographici: 125–127. [Original description of Cycas glauca and of Cycas rumphii var. timorensis; not consulted (BHL inaccessible), cited after Lindström et al. (2009).]
  • Lindström, A.J., Hill, K.D. & Stanberg, L.C. (2009). The genus Cycas (Cycadaceae) in Indonesia. Telopea 12(3): 385–418. doi:10.7751/telopea20095826 [Description, history, lectotypification, vernacular name, range and status (pp. 410–413); 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. [Very broad species concepts, Cycas glauca placed as a synonym of Cycas rumphii (p. 369); not consulted directly, cited after The World List of Cycads and Lindström et al. (2009).]
  • Lindström, A. (2023). Cycas glauca. The IUCN Red List of Threatened Species 2023-1: e.T178874A68901750. doi:10.2305/IUCN.UK.2023-1.RLTS.T178874A68901750.en [Current assessment (CR); reference checked on Crossref, category relayed by GBIF; Red List page not consulted (access blocked).]
  • Bösenberg, J.D. (2010). Cycas glauca. The IUCN Red List of Threatened Species 2010-3: e.T178874A7632756. doi:10.2305/IUCN.UK.2010-3.RLTS.T178874A7632756.en [Previous assessment; reference checked on Crossref, category not read.]
  • 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.]