Dioon spinulosum

Dioon spinulosum is a cycad of south-eastern Mexico that grows in the lowland and foothill rainforests of northern Oaxaca and Veracruz, often on limestone rocks. It is the tallest species of the genus Dioon: its slender trunk commonly passes 5 m and the published figures run from 10.7 m measured in the field to more than 15 m, and up to 16 or even 18 m in the oldest plants according to a 2020 revision. Its broad leaflets keep a row of small spines along the margin throughout the plant’s life, hence its name. Listed as Endangered by the IUCN, it is, with Dioon edule, one of the two Dioon most widely grown in Florida, where it is known as the giant dioon, but it dislikes frost: outdoors in Europe it has only been reported on the mildest Mediterranean coasts, where it has taken brief frosts of −1 to −2 °C (30 to 28 °F).

Key facts about Dioon spinulosum

  • Accepted name: Dioon spinulosum Dyer ex Eichler (1883), accepted by The World List of Cycads (version 2026.08.15) and by Kew’s World Checklist of Vascular Plants, the database behind POWO (June 2026 version, published on GBIF)
  • Former names and synonyms: no heterotypic synonym; the name Dioon spinulosum Dyer, published a year later (1884), is treated as a later homonym of the same plant
  • Family: Zamiaceae, order Cycadales
  • Common names: giant dioon (University of Florida); in Mexico coyolillo, coyolito de cerro, palma de chicle, palma de chicalite, chicalito, palma de dolores and others (see Common names)
  • Natural range: Mexico, northern Oaxaca and Veracruz, between 50 and 600 m above sea level
  • IUCN status: Endangered (EN A2acd+4acd; B1ab(iii,v)), assessment by A.P. Vovides, J. Chemnick and T. Gregory published in 2022
  • CITES and other protection: CITES Appendix II; Annex B in the European Union; “in danger of extinction” (P) under the Mexican standard NOM-059-SEMARNAT-2010
  • Documented hardiness: −2 °C (28 °F) for one morning without damage in a pot, and −1 °C (30 °F) with drying winds, foliage slightly bronzed, in the ground (south of France); USDA zones 9b to 11 according to the University of Florida (see Cold hardiness)
  • Light and soil: part shade to full shade according to the University of Florida; well-drained soil, watered in summer
  • Habit and adult size: plants (3) 5 to 16 m tall, up to 18 m; trunk 18 to 25 cm across; leaves 1 to 2.5 m long (2020 revision)
  • In the UK, US and Australia: Kew, Edinburgh, Wisley, Eden Project and other gardens (BGCI); Missouri Botanical Garden (a female plant donated in 1918), Montgomery Botanical Center (30 accessions), Lotusland and some forty other American gardens; Royal Botanic Gardens Victoria (outdoor beds), Royal Botanic Garden Sydney and other Australian gardens
  • Toxicity: treat as poisonous, especially the seeds (see Toxicity and precautions)

How to recognise Dioon spinulosum

Dioon spinulosum is recognised by its tall, relatively slim trunk, its very long leaves and its broad leaflets whose margins carry about ten small spines, even on adult plants. The revision of the genus published in 2020 by Hernández-Tapia, Jiménez-Ramírez and Vovides describes it as follows:

  • Habit: plants 5 to 16 m tall, rarely only 3 m or up to 18 m; trunk 18 to 25 cm in diameter;
  • Leaves: 8 to 40 in the crown, 100 to 250 cm long and 20 to 40 cm wide; the lowest leaflets are reduced to spines along the petiole (pinnacanths);
  • Leaflets: 60 to 130 pairs, sickle-shaped, 1.3 to 1.8 cm wide, the middle ones 7.4 to 19 cm long; margin with 8 to 12 spines, rarely 6 to 15;
  • Male cones: cylindrical to ovoid, 21 to 50 cm long;
  • Female cones: cylindrical to ovoid, 35 to 50 cm long and 20 to 27 cm wide, on a long stalk;
  • Seeds: ovoid to ellipsoid, 3.4 to 4.8 cm long, with a yellow sarcotesta.

August Wilhelm Eichler’s original description (1883), read in the copy held by The Cycad Society, was based on young plants without cones. Its largest leaf was only 65 cm long, with 38 pairs of leaflets 10 to 13 cm long and 13 to 16 mm wide, each with about 18 veins and some seven sharp, forward-pointing teeth 3 to 4 mm long on both margins from the lower third upwards. Eichler stressed three differences from Dioon edule: leaflets toothed on every leaf and much broader; lower leaflets reduced to small spiny teeth right down to the base of the leaf, so that no bare petiole is visible on mature leaves; and foliage glossy, pure green on both sides once the juvenile wool has gone, instead of matt and often bluish. He also noted that at first sight the plant looks more like an Encephalartos, recalling Encephalartos hildebrandtii, but that the way the base of each leaflet runs down the rachis is that of Dioon.

The female cones are so heavy that they end up hanging below the crown. Charles J. Chamberlain, who studied the species in the field in the early twentieth century, describes them as more than 20 inches (about 50 cm) long and weighing more than 30 pounds (about 14 kg), with two or three hundred seeds about an inch and a half (about 4 cm) long. He also observed growth rings in the trunk, one forming with each new crown of leaves.

Hybrids

No natural or garden hybrid of Dioon spinulosum has been documented.

Possible confusion

With Dioon rzedowskii

This is its closest relative, which grows in the same part of northern Oaxaca, a little higher up, on limestone slopes. According to the 2020 revision, Dioon rzedowskii loses the marginal spines of its leaflets as it ages, whereas Dioon spinulosum keeps them all its life (6 to 15 per leaflet), and its petiole lacks the basal spines (pinnacanths); its seeds are usually ovoid, those of Dioon spinulosum usually ellipsoid. Young plants of both species are spiny and hard to tell apart without knowing their origin.

With Dioon mejiae

Dioon mejiae, from Honduras and Nicaragua, belongs to the same group of tall, trunk-forming Dioon. According to the 2020 revision, its adult leaflets have entire margins, rarely with 1 to 3 spines, and its seeds are globose with a cream sarcotesta. In the wild it grows in drier, deciduous tropical forest rather than rainforest, and its origin is usually enough to rule it out.

With Dioon purpusii and Dioon edule

Dioon purpusii also has spiny leaflets, but it is a short-trunked plant (1.5 to 2 m) of the Oaxacan canyons between 900 and 1,750 m, with keeled leaves and shorter leaflets (5 to 9 cm in the original description). Dioon edule has narrower leaflets (0.4 to 1.5 cm) with smooth margins on adult plants and a trunk that rarely exceeds 1.5 m in the wild. Seedlings of Dioon edule do, however, have spiny leaflets, as Chamberlain noted.

Taxonomy

Dioon spinulosum was described in 1883 by August Wilhelm Eichler in the Berlin Gartenzeitung (2: 411–413, figure on pp. 438–439). Eichler explains that the plant had reached Europe the year before, at almost the same time and in two places: a dried leaf sent to William Thiselton-Dyer at Kew by C.J. Hoge from Yucatán, and a living plant sent to the Berlin botanic garden by the collector E. Kerber from a commercial nursery at Córdoba, Veracruz, whose owner said it grew wild in ravines near Tuxtla, followed by some forty more plants. The two botanists had agreed that Dyer would publish the name, which he did in the Biologia Centrali-Americana (1884); the 2020 revision treats that later publication as a homonym. The holotype, at Kew, is Hoge’s collection from a plant cultivated at Progreso, Yucatán (The World List of Cycads; 2020 revision). Chamberlain showed in 1912 that the species does not grow wild in Yucatán. The name has never changed and no synonym is recorded; the 2020 revision regards “Dioon spinulosum var. spinulosum”, found in some lists, as an invalid name.

According to the 2020 revision, which follows the phylogeny of Dorsey and colleagues (2018), Dioon spinulosum forms the Spinulosum clade with Dioon rzedowskii and Dioon mejiae, the clade of the tall, trunk-forming Dioon; the other species fall into the Edule, western and southern clades.

Etymology and history

The epithet comes from the Latin spinulosus, “covered with small spines”, a reference to the spiny leaflet margins (Haynes 2022, as given by The World List of Cycads). Chamberlain saw in it an example of recapitulation: seedlings of Dioon edule have spiny leaflets, like adult plants of Dioon spinulosum.

Chamberlain tells the story of its discovery in the wild in The Living Cycads (1919). After seeing a small potted plant in a park in Veracruz in 1906, he made enquiries through correspondents and two years later set off for the mountains beyond Tuxtepec, where it had been located. On the way, near Tierra Blanca, he found “splendid specimens” on the Hacienda de Joliet, a plantation owned by people from Joliet, Illinois, growing on limestone rocks in the shade of Spanish cedar, mahogany and ceiba. He measured one plant at 35 ft (about 10.7 m); his colleagues Barnes and Land found plants of 50 ft (about 15 m) a few months later. Beyond Tuxtepec, the plant was so abundant that “it would not be exaggerating to speak of a Dioon forest”. Chamberlain considered it the tallest of all cycads after one Australian species, which he called Macrozamia hopei, now Lepidozamia hopei.

How tall does it grow?

The published figures point the same way, with some differences that are worth setting out:

  • Chamberlain (1919) measured one plant at 35 ft (10.7 m), wrote that plants of 10 to 30 ft (3 to 9 m) are “not uncommon”, and reported plants of 50 ft (15 m) found by his colleagues; the caption of his photograph at Tierra Blanca gives the tallest plant as about 32 ft (9.8 m);
  • Jody Haynes, of the Montgomery Botanical Center, writes that some specimens soar to “more than 50 feet” (over 15 m) and that it is the tallest cycad of the New World and the second tallest in the world;
  • the 2020 revision gives (3) 5 to 16 (18) m and states that the species reaches 18 m “in the oldest specimens”.

No detailed measurement supports the 18 m figure; 15 m is supported by two independent sources. In cultivation, the University of Florida expects 5 to 12 ft (1.5 to 3.7 m).

Common names

In English, the University of Florida calls it giant dioon, and the Californian nursery Jungle Music uses the same name. “Gum palm”, sometimes given, is not documented by any reliable source. In Mexico, Species+ lists coyolillo, coyolito de cerro, palma de chicle and palma de dolores; the 2020 revision adds palma de chicalite and chicalito, and the 2019 update of the Mexican standard NOM-059 also lists espadaña, palma, palma canillo, palma cordoncillo and palma navaja. Palma de dolores is also used for Dioon edule.

In the wild

Dioon spinulosum grows in northern Oaxaca and Veracruz, between 50 and 600 m above sea level according to the 2020 revision, which cites collections around Tuxtepec, San José Chiltepec, Valle Nacional, Jacatepec, Soyaltepec and Acatlán de Pérez Figueroa in Oaxaca and Tezonapa in Veracruz. With Dioon rzedowskii, it is the only species in the genus that grows only in tropical rainforest, in very wet regions. Chamberlain found it on limestone rocks in the shade of a tall forest heavy with orchids, bromeliads and ferns, often on rocks with little soil, its roots exposed.

A small beetle, Pharaxonotha woodruffi, lives in its cones; it was described in 2022 by Skelley, Tang and Pérez-Farrera, who found it only on Dioon spinulosum, in north-eastern Oaxaca.

Conservation status and regulation

Dioon spinulosum is listed as Endangered (EN) on the IUCN Red List, in the assessment by A.P. Vovides, J. Chemnick and T. Gregory dated July 2020 and published in 2022, under criteria A2acd+4acd and B1ab(iii,v): a past and projected decline linked to habitat loss and exploitation, and a small range in which the habitat is deteriorating (The World List of Cycads; Crossref).

The species is listed in CITES Appendix II, like the whole family since 4 February 1977, with annotation #4 (CoP20 version, in force since 5 March 2026), which exempts seeds and pollen among other items. In the European Union it is in Annex B of Regulation (EC) No 338/97, whose current annexes are set by Regulation (EU) 2026/1383, applicable since 29 June 2026. In Mexico, the standard NOM-059-SEMARNAT-2010 lists it as “in danger of extinction” (category P), a category kept in the update of 14 November 2019.

Databases checked on 26 October 2026 (Species+, GBIF, The World List of Cycads, Crossref). This information does not replace the official texts: check the regulations in force before any purchase and prefer seed-grown plants.

Growing Dioon spinulosum

Dioon spinulosum grows faster than Dioon edule, according to several growers, but it needs warmth all year and does not tolerate prolonged frost. The University of Florida (UF/IFAS) recommends it for southern Florida, as an alternative to the queen sago, and gives these guidelines:

  • Light: part shade to full shade, whereas Dioon edule prefers sun;
  • Soil: well drained and irrigated, although the plant is drought-tolerant once established; a balanced fertiliser with trace elements improves growth;
  • Size in cultivation: 5 to 12 ft (1.5 to 3.7 m) tall and about 6 ft (1.8 m) across.

Outdoor and in-ground cultivation

Outdoors, the species belongs to frost-free or almost frost-free climates, which the University of Florida translates as USDA zones 9b to 11. Jungle Music, in coastal southern California, writes that it can take full sun in the tropics or right on the coast but always looks best with morning sun or strong filtered light, and suggests Dioon mejiae for full-sun positions; the nursery calls it the Dioon most likely to be found in a nursery. In Europe, a grower in Barcelona, Spain, reports on the French forum Fous de palmiers that his plants in the ground grow much faster than those in pots, each producing one flush of leaves a year, and that one of them, planted eight years earlier, produced its first cone, a male one, in 2014. A grower on the Côte Bleue, near Marseille in the south of France, describes a bright yellow-green flush in full sun and steady growth.

Container cultivation

In cooler climates, including the United Kingdom, it is a plant for a large pot moved under glass in winter, or for a heated glasshouse. A free-draining mix and an almost dry winter limit the risk of rot: in Ravenna, northern Italy, a grower reports on the Italian forum Tropicamente that part of the trunk of his plant rotted during a winter spent in a conservatory, and that the plant then reshot from four buds once the soft tissue had been cut away (2009). No observation on this species has been published by the Jardin zoologique tropical at La Londe-les-Maures, in the south of France.

In cultivation in the UK, US and Australia

  • United Kingdom: the Royal Botanic Gardens, Kew, the Royal Botanic Garden Edinburgh (also in its Garden Explorer catalogue), RHS Garden Wisley, the Eden Project, the Chelsea Physic Garden, Glasgow Botanic Gardens, Paignton Zoo, the National Botanic Garden of Wales, Treborth, Birmingham Botanical Gardens and The Living Rainforest declare the species to BGCI PlantSearch; no outdoor planting in Britain is documented.
  • United States: at the Missouri Botanical Garden, in St Louis, a female plant donated in 1918 by a private collector, D.S. Brown, still grows; its trunk measured 203.2 cm tall and 21.6 cm across when the 2025 article was written, and it is the only female among the garden’s eleven accessions of the species (Deloso and co-authors, 2025). The Montgomery Botanical Center, at Coral Gables in Florida, holds 30 accessions in its online catalogue, nine of them from 2012 and eleven from 2021, the year being taken from the accession number. At Ganna Walska Lotusland, in Santa Barbara, California, a large, old plant that was Madame Walska’s “favorite” cycad stands along the path of the Cycad Garden (summer 2026 newsletter). Fairchild Tropical Botanic Garden, The Huntington, the San Diego Botanic Garden, the San Diego Zoo, the University of California Botanical Garden at Berkeley, Naples Botanical Garden, Longwood Gardens, The New York Botanical Garden, the United States Botanic Garden and some thirty other gardens also declare it to BGCI.
  • Australia: the Royal Botanic Gardens Victoria grow it in outdoor beds at Melbourne Gardens (online plant census); the Royal Botanic Garden Sydney lists it in its catalogue, and Brisbane Botanic Gardens Mount Coot-tha, Cairns, Adelaide, James Cook University in Townsville, Bundaberg, Hunter Region Botanic Gardens and the University of Melbourne System Garden declare it to BGCI.

Propagation

Dioon spinulosum is propagated from seed; a male and a female plant are needed to obtain fertile seed. Seeds, which are exempt from CITES controls, are the simplest way to obtain plants of known origin. The Ravenna plant that reshot from several buds after trunk rot shows that the plant can produce new growth points, but no source describes propagation by offsets for this species.

Pests and diseases

No disease specific to the species is documented. In cultivation the main risk is rot of the trunk and roots in a cold, wet mix, as the Ravenna case shows.

Cold hardiness

Dioon spinulosum is one of the least hardy Dioon: its foliage suffers from −1 to −2 °C (30 to 28 °F), especially in wind. The University of Florida recommends it only for USDA zones 9b to 11, that is, an average annual minimum above about −3.9 °C (25 °F); Jungle Music claims cold tolerance down to about −7 to −5 °C (20 to 23 °F, “lower 20’s F”), a commercial assessment that no dated report confirms.

Mediterranean and European experience

  • Côte Bleue, Bouches-du-Rhône, France: a grower reports on the Fous de palmiers forum that his plant, in a pot outdoors under a south-facing terrace, took −2 °C (28 °F) one morning in winter 2012–2013 without damage (November 2013). After two winters outdoors he planted it out in spring 2015; it was intact in October 2015. During the cold spell of January 2017, with a minimum of −1 °C (30 °F) and drying winds, it was “slightly bronzed on top” but in fair condition (February 2017); in 2018 he added that he had never had less than −1 to −2 °C (30 to 28 °F) in five years.
  • Roussillon, France (USDA zone 9b): a grower reports on the same forum leaf damage from −1 to −2 °C (30 to 28 °F) and defoliation at −4 to −6 °C (25 to 21 °F), without giving a date or the growing conditions, and keeps the species for pots moved into frost-free shelter (2009).
  • Barcelona, Spain: a grower reports on the Fous de palmiers forum that his plants, in pots and in the ground, take occasional late-night frosts of −1 to −2 °C (30 to 28 °F) without damage; in his view, wind burns the leaves from −2 °C (28 °F), in a 2013 post.
  • Naples, Italy: a grower reports on the Tropicamente forum that his five plants in 50 cm pots, mulched up to above the bud and wrapped in a double layer of fleece from late December to March, suffered little in winter 2008–2009, with only a few reddened tips.
  • Rome, Italy: on the same forum, a grower reports that an adult plant kept in a cold glasshouse lost its leaves every winter for four years and then died (2009).

Taken together, these reports suggest leaf damage from −1 to −2 °C (30 to 28 °F) and a risk of defoliation around −4 °C (25 °F); this is a summary of isolated reports, not a measurement. The Jardin zoologique tropical at La Londe-les-Maures has published no observation on the species.

United Kingdom, United States and Australia

In the United States, the University of Florida restricts it to zones 9b to 11, which in Florida means the southern part of the state. In coastal southern California, Jungle Music sells it as a garden plant and an old specimen grows in the open in the Cycad Garden at Lotusland, in Santa Barbara, but no minimum temperature is published for either. In Australia, the Royal Botanic Gardens Victoria grow it in outdoor beds at Melbourne Gardens, again without a published temperature record. In the United Kingdom, no outdoor planting or trial has been reported.

Toxicity and precautions

Dioon spinulosum should be treated as poisonous, especially its seeds. Cycads contain toxic glycosides (cycasin, macrozamin), from which methylazoxymethanol is derived, a toxin affecting the liver and the nervous system. No analysis specific to the species is documented; a Japanese study (Yagi, 2004) did not detect these glycosides in the adult leaves of the three Dioon it analysed, but the risk from cycad seeds is well documented, particularly for dogs. Chamberlain reports that the seeds were ground into meal for tortillas, which implies a lengthy traditional preparation.

Wear gloves when handling the seeds, and keep plants and seeds out of reach of children and pets. If any part has been eaten, contact a poison centre, a doctor or a vet without delay.

Traditional uses

According to Chamberlain (1919), the large seeds of Dioon spinulosum provided meal for tortillas, as did those of Dioon edule, and children played with the hard, stony seed coat, with a hole cut in both ends. The 2020 revision confirms that the seed husks are used to make bullroarers (zumbadores) and mentions above all an ornamental use. Bonta and colleagues (2019) note that the species is planted outside its range, for instance in a park in Tepic (Nayarit). No recent source describes present-day consumption of the seeds.

Frequently asked questions

Can Dioon spinulosum be grown outdoors in the UK?

No. Its foliage is damaged from −1 to −2 °C (30 to 28 °F), and no outdoor planting has been documented in Britain. In Europe, outdoor plants have only been reported on the mildest Mediterranean coasts; elsewhere, grow it in a large pot and bring it into a bright, frost-free place for the winter.

How tall does it get?

Over 15 m (49 ft) in the wild. Chamberlain measured a plant of 10.7 m (35 ft) and his colleagues saw some of 15 m (50 ft); the 2020 revision gives up to 16 m, even 18 m (52 to 59 ft). In cultivation, the University of Florida expects 1.5 to 3.7 m (5 to 12 ft).

How can it be told from Dioon rzedowskii?

By the margins of adult leaflets. Dioon spinulosum keeps 6 to 15 spines on each leaflet throughout its life and has spines at the base of the petiole; Dioon rzedowskii loses its spines as it ages. Young plants of the two species look alike.

Sun or shade?

Part shade, preferably. The University of Florida recommends part or full shade, as it is an understorey plant of the rainforest, and Jungle Music finds that plants always look best with morning sun or filtered light. It does tolerate sun near the coast: a grower on the Côte Bleue describes its new leaves as bright yellow-green in full sun.

Does it grow fast?

Yes, for a Dioon. A grower in Barcelona sees his plants in the ground produce one flush a year and grow much faster than in pots; one produced its first cone after eight years in the ground.

Is it poisonous?

Yes, it should be treated as such, especially the seeds, like all cycads. Remove ripe female cones if animals have access to the garden, and call a poison centre if any part is eaten.

Is it endangered?

Yes. It is listed as Endangered by the IUCN (assessment published in 2022), because of the loss of its forest habitat, and protected under CITES Appendix II.

Further reading on Succulentes

Sources

Reference sites

Bibliography

  • Eichler, A.W. (1883). Ein neues Dioon (Dioon spinulosum Dyer). Gartenzeitung (Berlin) 2: 411–413, 438–439. [Original description: leaf sent to Dyer by C.J. Hoge (Yucatán) and living plants from a nursery at Córdoba (Veracruz); comparison with Dioon edule; copy held by The Cycad Society.]
  • Thiselton-Dyer, W.T. (1884). Cycadaceae. Biologia Centrali-Americana, Botany 3: 190–195. [Second publication of the name, treated as a homonym by the 2020 revision.]
  • Chamberlain, C.J. (1919). The Living Cycads. University of Chicago Press, Chicago. [Discovery in the wild, measured and reported heights, cones, seeds, growth rings, uses; full text (Internet Archive).]
  • Hernández-Tapia, J.E., Jiménez-Ramírez, J. & Vovides, A.P. (2020). Taxonomic revision of the genus Dioon (Zamiaceae). Phytotaxa 442(4): 267–290. doi:10.11646/phytotaxa.442.4.2 [Description, altitudes, habitat, common names, Spinulosum clade; treatment (Plazi). Revision criticised by Haynes (2020).]
  • Dorsey, B.L., Gregory, T.J., Sass, C. & Specht, C.D. (2018). Pleistocene diversification in an ancient lineage: a role for glacial cycles in the evolutionary history of Dioon Lindl. (Zamiaceae). American Journal of Botany 105: 1512–1530. doi:10.1002/ajb2.1149 [Four clades; abstract.]
  • Skelley, P.E., Tang, W. & Pérez-Farrera, M.A. (2022). Review of Pharaxonotha Reitter (Coleoptera: Erotylidae: Pharaxonothinae) inhabiting the cycad genus Dioon Lindl. (Cycadales), with descriptions of nine new species and comments on P. kirschii Reitter. Insecta Mundi 0917: 1–41. doi:10.5281/zenodo.6391973 [Pharaxonotha woodruffi on Dioon spinulosum; key (Plazi).]
  • Bonta, M., Pulido-Silva, M.T., Diego-Vargas, T., Vite-Reyes, A., Vovides, A.P. & Cibrián-Jaramillo, A. (2019). Ethnobotany of Mexican and northern Central American cycads (Zamiaceae). Journal of Ethnobiology and Ethnomedicine 15: 4. doi:10.1186/s13002-018-0282-z [Plant grown outside its range; open-access article.]
  • Yagi, F. (2004). Azoxyglycoside content and β-glycosidase activities in leaves of various cycads. Phytochemistry 65: 3243–3247. doi:10.1016/j.phytochem.2004.09.013 [Cycad glycosides, the case of Dioon; abstract.]
  • Deloso, B.E., Colligan, A., Sucher, R. & Ramirez, V. (2025). Missouri Botanical Garden’s cycad collection: a journey through time. Plant Species Biology. doi:10.1111/1442-1984.12509 [The female Dioon spinulosum donated in 1918 and the garden’s other accessions; open-access article.]
  • Vovides, A.P., Chemnick, J. & Gregory, T. (2022). Dioon spinulosum. The IUCN Red List of Threatened Species 2022: e.T42149A69830202. doi:10.2305/IUCN.UK.2022-1.RLTS.T42149A69830202.en [Endangered; reference checked on Crossref.]
  • Haynes, J.L. (2022). Etymological compendium of cycad names. Phytotaxa 550(1): 1–31. doi:10.11646/phytotaxa.550.1.1 [Etymology, as given 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.]