Cycas calcicola

Cycas calcicola is a cycad endemic to the Top End, the northern part of Australia’s Northern Territory, where it grows on the rocky high points of open woodland between Katherine, the Daly River basin and Litchfield National Park. Described in 1978 by John Maconochie, this member of the genus Cycas is recognised by its flat leaves bearing a very large number of very narrow leaflets, permanently hairy beneath, and by its silvery new growth, which rises from the ashes after the dry-season fires. Its name recalls the limestone outcrops where it was first collected, but it also grows on sandstone and shale. The IUCN classes it as Vulnerable, and a 2022 genomic study showed that botanic gardens hold only part of its genetic diversity.

Key facts about Cycas calcicola

  • Accepted name: Cycas calcicola Maconochie (1978), accepted by The World List of Cycads (version 2026.08.15); 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: none; no subspecies
  • Family: Cycadaceae, order Cycadales
  • Common names: fire fern, a local Northern Territory name for the new fronds that this species and Cycas armstrongii put up after fire (PACSOA, 1990); names in four Aboriginal languages (see Common names)
  • Natural range: Australia, Northern Territory: Daly River basin and Finniss Range, from Katherine to the north of Litchfield National Park
  • IUCN status: Vulnerable (VU A4cd; B2ab(i,ii,iii,iv,v)), assessment by N. S. Nagalingum and J. Clugston (2021) 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: exposed rocky summits in open woodland; limestone, sandstone, sandy alluvium and shale
  • Habit and adult size: trunk usually up to 2 m, rarely 4 or 5 m, 16 to 22 cm across; flat leaves 60 to 130 cm long
  • In the UK, US and Australia: five accessions of 1997 at Montgomery Botanical Center (Florida); listed by Honolulu Botanical Gardens in BGCI PlantSearch; no record in British gardens (see In cultivation in the UK, US and Australia)
  • Toxicity: no data specific to the species; treat it as poisonous, like all Cycas (see Toxicity and precautions)

How to recognise Cycas calcicola

Ken Hill (1996) separates it from the other Australian Cycas by its flat leaves carrying a very large number of very narrow leaflets that stay hairy beneath, and by its slender, spindle-shaped male cones. The description below follows Hill (1996) and the Flora of Australia:

  • Trunk: up to 2 m, rarely 4 m according to Hill (5 m according to the Flora of Australia), 16 to 22 cm in diameter.
  • Leaves: 60 to 130 cm long, flat in section (the two rows of opposite leaflets form an angle of 180°), with 210 to 410 leaflets; petiole 18 to 30 cm, densely covered in grey-white down, spiny along 10 to 50 % of its length.
  • Median leaflets: 5 to 12 cm long and 2.5 to 4 mm wide (rarely 5 mm), crowded (4 to 6 mm apart), with rolled-under margins and an abruptly tapering tip; at first hairy above, then hairless, glossy, dark slightly bluish green (not glaucous), densely covered beneath with brown-white hairs.
  • New growth and cataphylls: new growth densely covered in grey-white hairs mixed with a few orange ones; cataphylls soft, not pungent, 3 to 6 cm long, with grey-white down.
  • Male cones: spindle-shaped, 25 to 30 cm long and 5 to 7 cm across, orange to orange-brown; microsporophylls ending in a fine, sharply upturned spine 7 to 10 mm long.
  • Megasporophylls: 12 to 18 cm long, with grey and orange down, bearing 4 to 6 ovules; blade 20 to 25 mm long, regularly toothed (26 to 36 lateral teeth), terminal spine 6 to 10 mm.
  • Seeds: flattened-ovoid, green turning orange, strongly glaucous, 28 to 31 mm long and 27 to 30 mm wide; sarcotesta 2.5 to 3 mm thick.

The leaflets have the anatomy of a plant of dry places: a continuous layer of cells beneath the epidermis, stomata sunk in deep, closed pits and a very thick cuticle (Hill 1996). The Palm and Cycad Societies of Australia (PACSOA) describes upright new fronds of an intense silver.

Hybrids

Natural populations of probable hybrid origin are known, but no garden hybrid. Hill (1996) cites herbarium specimens intermediate between Cycas calcicola and Cycas conferta, collected at Blackfellows Creek in 1993, and reports apparent hybrids with Cycas calcicola within the range of Cycas conferta. An article published in 1990 in the PACSOA magazine, reproduced on the society’s website, also reports that a Darwin naturalist was convinced that hybrids with Cycas armstrongii exist where the two species meet (Florence Falls, north of Katherine, the upper Daly River); this suggestion is not taken up in Hill’s revision.

Possible confusion

In the wild, confusion is possible mainly with the other Cycas of the Top End; in the trade, with plants sold under a false name:

  • Cycas arenicola, the only other Australian species whose adult leaflets are densely hairy beneath: fewer leaflets (180 to 270), broader (4 to 6.5 mm), more widely spaced (8 to 14 mm) and gradually tapering to the tip (Hill 1996);
  • Cycas armstrongii and its relatives (Cycas conferta, Cycas canalis), with pungent cataphylls and leaflets more than 4 mm wide, without rolled-under margins;
  • Cycas arnhemica, of the same series, whose adult leaflets do not stay densely hairy, and Cycas maconochiei, also in the series, with leaflets more than 4 mm wide and not rolled under (Hill 1996);
  • in the trade: in February 2010, a grower from Belley (Ain) and Montpellier (Hérault), in France, warned on the French forum Fous de palmiers about a seller who offered Cycas siamensis under the name Cycas pruinosa, and the same plant under the name Cycas calcicola; seed or plants of documented origin are the safer choice.

Taxonomy

Cycas calcicola is a name accepted by The World List of Cycads, with no synonym; the World Checklist of Vascular Plants (WCVP), on which POWO is based, also accepts it (consulted through GBIF on 31 October 2026). John R. Maconochie described it in 1978 in the Journal of the Adelaide Botanic Gardens (volume 1, page 175, figure 1), in the same paper as Cycas pruinosa. The type (Maconochie 1314) was collected on 10 June 1971, 16 km north of Katherine; the holotype is kept at the Northern Territory Herbarium in Darwin (DNA), with isotypes at Brisbane, Canberra, Kew, Leiden and Perth (Hill 1996; The World List of Cycads).

In his revision of the Australian Cycas, Ken Hill (1996) made it the type species of series Calcicolosae, in subsection Endemicae of section Cycas. The series brings together four species from the north of the Northern Territory, with flat leaves, leaflets with more or less rolled-under margins and soft cataphylls: Cycas calcicola, Cycas arenicola, Cycas arnhemica and Cycas maconochiei. Hill nevertheless stresses that some characters, such as the orange down, link Cycas maconochiei with other species, and that these resemblances do not always allow clear-cut groupings.

Etymology and history

The epithet comes from the Latin calci-, “lime”, and recalls the limestone outcrops where the species was found (Haynes 2022, cited by The World List of Cycads); the suffix -cola means “dweller”. The name has proved partly misleading: Hill (1996) and the Flora of Australia point out that the species, described from limestone and named accordingly, also grows on non-calcareous substrates, sandstone, sandy alluvium and aluminous shale.

According to Len Butt’s article reproduced by PACSOA (1990), a slender-trunked Cycas with silvery new growth, forming great stands among limestone rocks, had long been reported in the Top End. Maconochie, botanist at the Northern Territory Herbarium, described it, giving its habitat as limestone outcrops and open forest north of Katherine, with two further populations, at Bamboo Creek on the Mandora Road south of Darwin and on the East Alligator River.

Common names

One English name is attested locally: fire fern. Len Butt’s 1990 article, reproduced on the PACSOA wiki, states that the new fronds that Cycas armstrongii and Cycas calcicola produce after the dry-season fires are known locally as “fire-fern”. The compendium of vernacular cycad names by Mark Bonta and Roy Osborne also gives names in four Aboriginal languages of the Northern Territory: walangkirrik in Malakmalak, turtur in Matngala, yerrsya for the plant and misya for the seeds in Ngan’gikurunggurr and Ngan’giwumirri, and ngewerrin in Wardaman. The first two are also given for Cycas canalis: they probably refer to cycads in general rather than to a single species.

In the wild

Cycas calcicola is endemic to the Northern Territory. According to Hill (1996) and the Flora of Australia, it is abundant around the Daly River basin and northwards along the Finniss Range, from Katherine in the south-east to the north of Litchfield National Park, and south to the area of the Daly River police station. It grows mainly on rocky summits, on limestone, sandstone, sandy alluvium and shale. The nurseryman Simon Lavaud (2021) writes that it grows on limestone and basalt alike, which neither Hill nor the Flora of Australia mentions. The genomic study by Clugston and colleagues (2022) sampled wild populations in Litchfield and around Katherine, together with botanic garden plants originally collected at Katherine, Daly River and the Spirit Hills.

According to PACSOA, in areas burnt every year by Aboriginal people, the stands of Cycas calcicola are the first to regain colour, with their silvery new growth. The Flora of Australia gives a fruiting period from October to May. From the Katherine climate records discussed by Simon Lavaud (2021), nights there can fall to around 15 °C (59 °F), days stay above 30 °C (86 °F) for almost the whole year, rainfall exceeds 1,000 mm a year, and the coolest months are also the driest.

Conservation status and regulation

Cycas calcicola is classed as Vulnerable (VU) by the IUCN, under criteria A4cd and B2ab(i,ii,iii,iv,v), as The World List of Cycads states. According to Crossref metadata, the latest assessment, by N. S. Nagalingum and J. Clugston, dated 20 October 2021, was published in Red List version 2023-1; the previous one, by Ken Hill, dates from 2010. GBIF confirms the category. In 1996, by contrast, Hill regarded the species as widespread and not at risk.

The study by Clugston and colleagues (2022), based on 2,271 genetic markers (SNPs), found low to moderate genetic diversity, very little gene flow between populations and high inbreeding (mean FIS of 0.491). The populations fall into two genetic groups, Katherine on one side and Litchfield, Daly River and the Spirit Hills on the other. The botanic garden collections studied had markedly lower genetic diversity than the wild populations and did not represent those of Litchfield National Park; the authors recommend expanding them and managing the Katherine and Litchfield populations separately.

Like every species in the genus except Cycas beddomei, Cycas calcicola 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 and tissue cultures obtained in vitro and transported in sterile containers, and cut flowers of artificially propagated plants, are not covered by CITES, whereas international trade in plants 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, confirms this status (consulted on 17 October 2026). A specific protection under Northern Territory law could not be verified.

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

Growing Cycas calcicola

In short: a tropical plant reputed to be very difficult outside the tropics; no institution has published recommendations for it, and no dated report of long-term cultivation in Europe, Britain or North America has been published. In its home region it is grown: PACSOA shows a plant cultivated at Katherine, and a member of the French forum Fous de palmiers living in Thailand photographed plants at the George Brown Darwin Botanic Gardens and at Bamboo Creek, in Litchfield National Park, in September 2016.

Outdoor and in-ground cultivation

Simon Lavaud (Cycadales.eu), in his 2021 note on growing Australian Cycas in a European climate, classes all the Northern Territory species except Cycas angulata as “very difficult” in a temperate climate. He shows a Cycas calcicola grown at Nong Nooch Tropical Garden in Thailand (photograph of 2019), where, in his view, the Australian Cycas thrive thanks to almost constant temperatures of 25 to 30 °C (77 to 86 °F) and a short dry season; a specialist he quotes considers that they grow even better there than in Darwin. He also points out that in Europe the coolest months are the wettest, the reverse of the Katherine climate. By simple deduction, the same reversal applies to other climates with winter rain, such as coastal California or southern Australia; no outdoor trial of the species in those regions has been published.

Container cultivation

In France, a grower from Belley (Ain) and Montpellier (Hérault) reported on the Fous de palmiers forum in December 2010 that seeds of Cycas calcicola had germinated indoors in midwinter; no later news of the seedlings is documented.

In cultivation in the UK, US and Australia

In short: outside its native region, the species is very rare in public collections. A garden listed in the BGCI PlantSearch database (consulted in October 2026) has declared the species at some point, which does not prove that a living plant is there today.

  • United States: the online catalogue of Montgomery Botanical Center (Coral Gables, Florida) lists five accessions of Cycas calcicola, whose numbers point to 1997. Honolulu Botanical Gardens (Hawaii) lists the species in BGCI PlantSearch.
  • Australia: none of the online catalogues consulted (Royal Botanic Garden Sydney, Mount Annan, Royal Botanic Gardens Victoria) lists the species, and no list is documented for the George Brown Darwin Botanic Gardens, where it was photographed in 2016. The botanic garden plants studied by Clugston and colleagues (2022) are not attributed to named gardens in the summary consulted.
  • United Kingdom: no British garden lists the species.

No report from a grower in the United Kingdom, the United States or Australia has been published on English-language forums.

Propagation

Like all Cycas, Cycas calcicola is dioecious: a male and a female plant are needed to obtain fertile seed. Propagation is from seed; the only report found is the indoor winter germination mentioned above, posted in 2010 on the Fous de palmiers forum. No germination data specific to the species has been published. Seeds are exempt from CITES under annotation #4; ask for seed from cultivated plants of documented origin.

Pests and diseases

No pest or disease specific to the species is documented. Cycad scale insects, including Aulacaspis yasumatsui, can attack any cultivated Cycas, and root rot in a cold, wet substrate is the cause of failure most often cited for Australian Cycas in Europe (Lavaud 2021).

Cold hardiness

There is no cold-tolerance data for Cycas calcicola. Its whole range lies in the tropical north of Australia, and nothing allows us to say that it tolerates frost. No USDA zone for the species is given by any reliable published source.

No cultivation result, in the ground or in a pot, has been published in Europe, the United States or temperate Australia, and no dated frost episode concerns it. On the Fous de palmiers forum, whose members garden largely in the south of France, it appears only as an indoor seedling, and the Jardin zoologique tropical in the Var has published no observation of it. In Italy, the species is only mentioned on the Tropicamente forum: in 2012, a grower in Ravenna counted it among the interesting blue Australian Cycas, while fearing that it would not tolerate the humidity of that region. Without data, the prudent course is a pot, frost-free and kept dry in winter.

Toxicity and precautions

No toxicity analysis specific to Cycas calcicola is documented. 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) among plants poisonous to dogs, cats and horses. Without 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 traditional use of Cycas calcicola is documented, although the existence of separate Aboriginal names for the plant and for its seeds shows that the species is known to local people. The food uses of the seeds of other Australian Cycas, after long detoxification, cannot be attributed to it without a source.

Frequently asked questions

Does Cycas calcicola grow only on limestone?

No. It was described from limestone outcrops, hence its name, but it also grows on sandstone, sandy alluvium and shale, mainly on rocky summits.

How can it be recognised?

By its flat leaves bearing 210 to 410 very narrow, crowded leaflets, permanently hairy beneath, and by its slender, spindle-shaped male cones. Cycas arenicola, the only other Australian species with leaflets hairy beneath, has fewer, broader and more widely spaced leaflets.

Why is its new growth silver?

Because it is covered in thick grey-white down. New fronds appear in numbers after the dry-season fires, and PACSOA describes them as the first return of colour in burnt areas; locally they are called “fire-fern”.

Is it threatened?

Yes. The IUCN classes it as Vulnerable, and a 2022 genomic study found low genetic diversity, little exchange between populations and high inbreeding.

Can it be grown outdoors in the UK or the cooler parts of the US?

Nothing suggests it can. There is no measurement of cold tolerance and no trial outside the tropics; it is a tropical plant, to be kept in a pot under glass and frost-free, and a specialist nurseryman considers it, like the other Northern Territory species, very difficult in a temperate climate.

Are plants sold under this name reliable?

Not always. In 2010 a seller was reported on the Fous de palmiers forum for offering Cycas siamensis under the names Cycas pruinosa and Cycas calcicola: choose suppliers who document the origin of their seed.

Is it poisonous?

It must be assumed so. There is no analysis specific to the species, but all the Cycas studied contain serious toxins, especially in the seeds.

Further reading on Succulentes

Sources

Reference sites

Bibliography

  • Maconochie, J.R. (1978). Two new species of Cycas from northern Australia. Journal of the Adelaide Botanic Gardens 1(3): 175–178. [Protologue; reference taken from The World List of Cycads and the Flora of Australia.]
  • Hill, K.D. (1996). A taxonomic revision of the genus Cycas (Cycadaceae) in Australia. Telopea 7(1): 1–64. doi:10.7751/telopea19963040 [Description, type, series Calcicolosae, key, anatomy, distribution, hybrids.]
  • Hill, K.D. (1998). Cycadaceae. In: McCarthy, P.M. (ed.), Flora of Australia 48: 597–635. CSIRO Publishing, Melbourne. [Consulted in its updated online version (profiles.ala.org.au).]
  • Clugston, J.A.R., Ruhsam, M., Kenicer, G.J., Henwood, M., Milne, R.I. & Nagalingum, N.S. (2022). Conservation genomics of an Australian cycad Cycas calcicola, and the absence of key genotypes in botanic gardens. Conservation Genetics 23(3): 449–465. doi:10.1007/s10592-022-01428-8 [Genetic diversity, population structure, ex situ collections.]
  • Nagalingum, N.S. & Clugston, J. (2023). Cycas calcicola. The IUCN Red List of Threatened Species 2023-1: e.T41989A67338115. doi:10.2305/IUCN.UK.2023-1.RLTS.T41989A67338115.en [Assessment dated 20 October 2021; reference found on Crossref, category confirmed by GBIF.]
  • Hill, K.D. (2010). Cycas calcicola. The IUCN Red List of Threatened Species 2010: e.T41989A10595908. [Previous assessment; cited by The World List of Cycads.]
  • Bonta, M. & Osborne, R. Cycads in the Vernacular: A Compendium of Local Names. The Cycad Society. http://www.cycad.org/documents/Bonta-Osborne-Cycads-Vernacular.pdf [Aboriginal names of the species.]
  • Butt, L.P. (1990). [Article on Cycas armstrongii and Cycas calcicola.] Palms & Cycads 27. [Known through its reproduction on the PACSOA wiki.]
  • Haynes, J.L. (2022). Etymological compendium of cycad names. Phytotaxa 550(1): 1–31. doi:10.11646/phytotaxa.550.1.1 [Etymology of the epithet; cited 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.]