Dioon califanoi

Dioon califanoi is a cycad from northern Oaxaca and southern Puebla, in Mexico, where it grows in the mountains between dry forest and pine-oak forest. This species of the genus Dioon is recognised by its strongly keeled leaves: the two rows of leaflets form a striking V of about 80°. Described in 1979 by two botanists from Naples, it is listed as Endangered by the IUCN and remains rare in cultivation, where it grows slowly. It has a reputation as one of the least tender Dioon, but outdoor trials in France have given mixed results: it came through a winter unprotected on the Mediterranean coast, lost its leaves at −5 °C (23 °F) in Brittany and did not survive wet winters in western France.

Key facts about Dioon califanoi

  • Accepted name: Dioon califanoi De Luca & Sabato (1979), accepted by The World List of Cycads (version 2026.08.15), GBIF and Kew’s World Checklist of Vascular Plants, the database behind POWO (June 2026 version, published on GBIF)
  • Former names and synonyms: no synonym accepted by The World List of Cycads
  • Family: Zamiaceae, order Cycadales
  • Common names: no English name is attested; “palma” (Oaxaca) according to the Mexican standard NOM-059
  • Natural range: Mexico, northern Oaxaca (between Teotitlán and Huautla) and southern Puebla; between 1,500 and 3,250 m according to its describers, at about 1,600 m (5,200 ft) for recent collections (see In the wild)
  • IUCN status: Endangered (EN A2cd; B1ab(i,ii,iii,v)), assessment by J. Chemnick and T. Gregory dated July 2020 and published in 2022
  • CITES and other protection: CITES Appendix II (annotation #4); Annex B in the European Union; “in danger of extinction” (category P) in Mexico
  • Documented hardiness: leaves destroyed and trunk sound at −5 °C (23 °F) in the ground (Concarneau, Brittany, winter 2011–2012); a young plant lost at −5 °C (23 °F) (Roussillon, southern France, 2009); a winter without protection and without damage on the Côte Bleue near Marseille (2015) (see Cold hardiness)
  • Light and soil: full sun according to a Californian nursery; very free-draining soil, dry in winter
  • Habit and adult size: trunk 3 m or more tall and 20 to 30 cm (8 to 12 in) across, reclining in very old plants; leaves 75 to 85 cm long or more
  • In the UK, US and Australia: Royal Botanic Gardens Victoria (outdoor beds at Melbourne Gardens), Royal Botanic Garden Sydney, Montgomery Botanical Center and the Fairchild Tropical Botanic Garden (Florida); declared to BGCI by Edinburgh, RHS Wisley and some twenty American gardens
  • Toxicity: to be treated as toxic, especially the seeds (see Toxicity and precautions)

How to recognise Dioon califanoi

Dioon califanoi is recognised by its stiff, strongly keeled leaves, folded into a V above the axis, with leaflets set obliquely above it. According to Gregory and colleagues (2003), the angle between the two rows of leaflets averages 80° in cross-section, and the almost spineless leaflets are glaucous once the down of the young leaves has fallen. The original description by Paolo De Luca and Sergio Sabato (1979) gives the following measurements:

  • Trunk: cylindrical, up to 3 m or more, 20 to 30 cm across, with leaf scars like those of Dioon spinulosum.
  • Leaves: numerous, keeled at a right angle, stiff and leathery, upright, woolly when young and then smooth, 75 to 85 cm long or more, with the axis spirally twisted near the tip, on a petiole 10 to 12 cm long.
  • Leaflets: about 80 to 100 on each side, linear-lanceolate, sharp-pointed, about 5 mm apart; the basal ones 2.5 to 3 cm long and entire; those in the middle and upper part 6 to 7 cm long and 7 to 8 mm wide, entire or with one spine on the upper margin.
  • Female cone: ovoid-cylindrical, about 50 cm long and 25 cm across, with densely woolly scales.
  • Seeds: ovoid to almost globose, 3 to 4 cm long and 2 to 2.5 cm wide.
  • Male cone: elongated-cylindrical, blunt, about 40 cm long and 10 cm across.

The leaflets are the size of those of Dioon edule. The Californian nursery Jungle Music describes a green to grey-green foliage, leaves about four to five feet (1.2 to 1.5 m) long and, in very old plants, trunks that lie down and crawl along the ground; it gives a 90° angle between the two rows of leaflets. A grower on the Côte Bleue notes on the French Fous de palmiers forum the very abundant white down of the young leaves (2011).

Hybrids

No natural or garden hybrid of Dioon califanoi is documented.

Possible confusion

With Dioon purpusii and Dioon argenteum

Gregory and colleagues (2003) group these three species from the canyons of the río Santo Domingo basin as the “Dioon purpusii complex”. Their leaves, leaflets and cones are of similar size, and they differ mainly in the keel of the leaves, the wax on the leaflets and how long the down lasts. Dioon purpusii has moderately keeled leaves (122° on average) and glossy, spiny leaflets; Dioon argenteum has almost flat leaves (164°) and a silvery down that lasts for at least a year.

With Dioon merolae

The 2020 revision regards Dioon merolae, from Chiapas, as its closest relative. Dioon merolae has flat leaves with very crowded, overlapping leaflets curved downwards, cataphylls with a long, tail-like tip and trowel-shaped female cone scales. Young plants can look alike.

With Dioon caputoi and Dioon edule

Dioon caputoi, from the dry high plateaux south of Tehuacán, has smaller leaves and much narrower, more widely spaced leaflets (Gregory et al., 2003). Dioon edule has leaflets of the same size; according to the original description, it is the keeled leaves and the oblique insertion of the leaflets above the axis that set Dioon califanoi apart from the species then known.

Taxonomy

Paolo De Luca and Sergio Sabato, of the University of Naples, described Dioon califanoi in 1979 in the journal Brittonia (31(1): 170–173), from a site in Oaxaca discovered during expeditions organised by the Accademia Nazionale dei Lincei. The holotype, collected by the two authors on 15 October 1974 between Teotitlán del Camino and the Huautla region, is kept in the Naples herbarium (NAP), with duplicates in Mexico City (ENCB), Chicago (F), Florence (FI), Geneva (G) and Ann Arbor (MICH) (The World List of Cycads). An older collection existed: that of C.E. Smith, F.A. Peterson and N. Tejeda, made on 3 August 1961. The authors also studied plants transplanted to the Naples botanic garden, the largest of which had a 1 m trunk.

The World List of Cycads accepts no synonym; the combination “Dioon edule var. califanoi”, listed by some databases, has not been verified. Gregory and colleagues (2003) considered treating Dioon califanoi, Dioon purpusii and Dioon argenteum as subspecies of a single species, then kept three recently diverged species. Gutiérrez-Ortega and colleagues (2021) place Dioon califanoi in the Purpusii clade, which includes most of the Dioon of Oaxaca and Chiapas.

Etymology and history

The epithet honours Luigi Califano (1901–1976), of the Accademia Nazionale dei Lincei, who had guided the authors in Mexico on their visits to Dioon sites (De Luca and Sabato, 1979; The World List of Cycads, after Haynes, 2022). The species is one of the many Dioon described by Paolo De Luca’s Naples team between 1979 and 1981, together with Dioon caputoi, Dioon rzedowskii, Dioon merolae and Dioon holmgrenii.

Common names

No English common name is attested. The Mexican standard NOM-059 simply gives “palma” for Oaxaca. The names “Califano’s cycad” or “palma de Califano”, sometimes put forward, are not documented in any reliable source.

In the wild

Dioon califanoi grows in northern Oaxaca and southern Puebla (The World List of Cycads). The type locality lies between Teotitlán del Camino and the Huautla region; Gregory and colleagues (2003) place the species in the east of the Tehuacán valley and then knew only two populations. Like Dioon purpusii and Dioon argenteum, it lives almost exclusively in the transition zone between tropical deciduous forest and pine-oak forest.

The published altitudes vary. In the description of Dioon holmgrenii (1981), De Luca and colleagues place it in dry pine-oak forest between 1,500 and 3,250 m, referring to their 1979 description; the collections of the beetle Pharaxonotha bicolor, published in 2022, come from 1,300 to 1,900 m across all its host plants, including Dioon califanoi at about 1,600 m near Teotitlán. The figure of 3,250 m has not been found elsewhere.

The male cones host the small beetle Pharaxonotha bicolor, described in 2022 and also known from Dioon purpusii and Dioon caputoi, and weevils of the genus Parallocorynus, including Parallocorynus gregoryi (Skelley et al., 2022; O’Brien and Tang, 2015).

Conservation status and regulation

Dioon califanoi is listed as Endangered (EN) on the IUCN Red List, in the assessment by J. Chemnick and T. Gregory dated 3 July 2020 and published in 2022, under criteria A2cd and B1ab(i,ii,iii,v): a decline in numbers linked to habitat loss and collecting, and a very restricted range in which the habitat is deteriorating (The World List of Cycads, GBIF and Crossref). The 2003 cycad action plan listed it as Vulnerable, with 3,000 to 5,000 adult plants, and named land clearance and collecting among the threats.

Like the whole genus since 4 February 1977, the species is listed in CITES Appendix II, with annotation #4 in the version adopted at CoP20, in force since 5 March 2026, which exempts seeds and pollen in particular. In the European Union it falls under Annex B of Regulation (EC) No 338/97, whose annexes are now 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).

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

Growing Dioon califanoi

Dioon califanoi is sought after by collectors for its sculptural foliage, but it grows slowly. The available sources give these guidelines:

  • Light: full sun on the coast and in much of the interior, but only a few hours of sun in desert climates, according to the Californian nursery Jungle Music.
  • Soil and watering: a very free-draining soil. The failures reported in France are mainly due to winter wet: in Nantes, a plant set out in 2007 died during an otherwise mild winter, probably from excess water despite good drainage (2011); another grower lost three- or four-year-old plants during rainy winters, even in a very free-draining mix (2011).
  • Growth: slow. In Ravenna, in northern Italy, a grower ranks it among his slowest cycads, with Dioon spinulosum (2009); he found its seeds easy to germinate, on the other hand.

Outdoor and in-ground cultivation

Plant only well-established plants, in a raised, very free-draining position, in full sun except in desert heat, and keep winter rain off the crown if the climate is wet. These recommendations follow from the French reports above; no observation from the Jardin zoologique tropical at La Londe-les-Maures has been published for this species.

Container cultivation

In a pot, a very open mineral mix, generous watering in summer and an almost dry, frost-free winter suit it; the plants lost in Ravenna were in pots kept outdoors and then in a very cold glasshouse (see Cold hardiness). Its slow growth means it can stay in a container for many years.

In cultivation in the UK, US and Australia

  • United Kingdom: the Royal Botanic Garden Edinburgh and RHS Garden Wisley declare the species to BGCI PlantSearch; no planting in the open ground is documented in Britain.
  • United States: the Montgomery Botanical Center (Coral Gables, Florida) lists four accessions in its online catalogue, one of them from 2001 (20011255), and the Fairchild Tropical Botanic Garden (Miami) lists the species in its online catalogue. BGCI PlantSearch also lists the Huntington, Lotusland, San Diego Botanic Garden, the San Diego Zoo, Naples Botanical Garden, UC Berkeley, the Los Angeles County Arboretum, the Atlanta Botanical Garden, the Living Desert, Marie Selby Botanical Gardens and Descanso Gardens, among others.
  • Australia: the census of the Royal Botanic Gardens Victoria (October 2026) lists Dioon califanoi in outdoor beds at Melbourne Gardens, and the Royal Botanic Garden Sydney lists it in its Garden Explorer; Brisbane Botanic Gardens Mount Coot-tha, the Cairns Botanic Gardens and the Adelaide Botanic Garden declare it to BGCI.

A BGCI listing is a declaration by the garden, not proof that the plant is alive today.

Propagation

Dioon califanoi is propagated from seed; a male and a female plant are needed to obtain fertile seed. Seeds, which are exempt from CITES permits, are the simplest way to obtain plants of known origin. A grower in Ravenna found them easy to germinate (Tropicamente forum, 2009). No source describes propagation by offsets.

Pests and diseases

No disease specific to the species is documented. In cultivation, the main risk is root and trunk rot in cold, wet soil, the probable cause of the failures reported in western France.

Cold hardiness

Dioon califanoi has a reputation as one of the least tender Dioon, and its trunk can survive frosts that destroy its leaves. The published trials show, however, that winter wet and the age of the plants count as much as the temperature.

Mediterranean and European experience

The reports below come from the French Fous de palmiers and Italian Tropicamente forums; they are amateur observations of indicative value.

  • Côte Bleue (Bouches-du-Rhône, near Marseille): a grower reports that he had planted his whole Dioon collection, including Dioon califanoi, and that all came through a winter without protection and without damage (October 2015). The same grower noted in 2018 that he had never recorded less than −1 or −2 °C (30.2 or 28.4 °F) in five years.
  • Roussillon (southern France, a garden the grower places in USDA zone 9b): a grower lost a Dioon califanoi at −5 °C (23 °F), during a dry winter, having planted it at two years old (2009).
  • Concarneau (Finistère, Brittany): during the winter of 2011–2012, with a low of −5 °C (23 °F), the leaves of a Dioon califanoi in the ground were destroyed, but the trunk remained perfectly sound (April 2012).
  • Nantes (Loire-Atlantique): a plant set out in 2007 died during a mild winter (−4 °C (24.8 °F) and few frost days), probably from excess water (January 2011).
  • Ravenna (Emilia-Romagna, Italy): a grower reports that his young plants, in pots outdoors sheltered from rain and wind, withstood −3 °C (26.6 °F) (2009). During the winter of 2009–2010, with −7 °C (19.4 °F) outside, they lost almost all their leaves in a very cold glasshouse; according to a post of April 2012, they did not survive in the end.

These reports suggest leaves destroyed at around −5 °C (23 °F), a trunk able to survive in established plants, and losses among young plants and in wet soils; this is a synthesis of isolated reports, not a measurement. For readers in mild Mediterranean-type climates (coastal California, southern Australia), the Côte Bleue experience is the most relevant; for the mild but wet climate of south-west England, the losses recorded in western France argue for great caution.

United Kingdom, United States and Australia

No dated report from a British, American or Australian grower has been found. In southern California, Jungle Music claims cold hardiness “into the low 20’s or a bit colder” (°F), about −5 to −7 °C (23 to 19.4 °F); this is a nursery’s assessment. In Melbourne, plants grow in outdoor beds at the Royal Botanic Gardens Victoria (see In cultivation), but no cold data are published for them. Figures of −10 °C (14 °F) circulate on forums without any verifiable observation.

Toxicity and precautions

Dioon califanoi should be treated as toxic, 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 has been published.

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

Traditional uses

No traditional use specific to Dioon califanoi is documented.

Frequently asked questions

Can Dioon califanoi stay outdoors all year?

Only in the mildest climates. On the French Mediterranean coast, a plant came through a winter without protection; elsewhere, trials have been disappointing: leaves destroyed at −5 °C (23 °F) in Brittany, plants lost in a wet winter in Nantes or when planted too young. Plant only well-established specimens, in very free-draining soil and sheltered from winter rain, or grow it in a pot.

Is it hardier than other Dioon?

The data do not settle it. Growers and nurseries describe it as one of the hardier species, but published observations are few: in Brittany its trunk survived −5 °C (23 °F) while the leaves were destroyed. The −10 °C (14 °F) sometimes quoted rests on no verifiable observation.

How can it be recognised?

By its leaves keeled in a V of about 80° and its glaucous, almost spineless leaflets. Dioon purpusii has more open leaves with glossy, spiny leaflets; Dioon argenteum has almost flat leaves with a persistent silvery down.

Does it grow fast?

No. It is one of the slowest Dioon in cultivation, according to a grower in Ravenna. Expect many years before a trunk forms.

Is it poisonous?

Yes, it should be treated as such, especially the seeds, like all cycads. Wear gloves to handle them and call a poison centre if any part has been eaten.

Is it endangered?

Yes. It is listed as Endangered by the IUCN (assessment published in 2022) and as “in danger of extinction” in Mexico. It is protected by CITES (Appendix II); buy seed-grown plants.

Further reading on Succulentes

Sources

Reference sites

Bibliography

  • De Luca, P. & Sabato, S. (1979). Dioon califanoi (Zamiaceae), a new species from Mexico. Brittonia 31(1): 170–173. [Original description: type, measurements, distinguishing characters, plants in Naples; copy published by The Cycad Society.]
  • De Luca, P., Sabato, S. & Vázquez Torres, M. (1981). Dioon holmgrenii (Zamiaceae), a new species from Mexico. Brittonia 33(4): 552–555. [Habitat and altitudes of Dioon califanoi; copy published by The Cycad Society.]
  • Gregory, T.J., Chemnick, J., Salas-Morales, S.H. & Vovides, A.P. (2003). A new species in the genus Dioon (Zamiaceae) from north-central Oaxaca, Mexico. Botanical Journal of the Linnean Society 141(4): 471–476. doi:10.1046/j.1095-8339.2003.t01-1-00151.x [Dioon purpusii complex, leaf angle, glaucous leaflets, known populations.]
  • Gutiérrez-Ortega, J.S., Pérez-Farrera, M.A., Chemnick, J. & Gregory, T.J. (2021). A reassessment of Dioon merolae (Zamiaceae) leads to the description of Dioon salas-moralesae, a new cycad species from Southeastern Oaxaca, Mexico. Phytotaxa 528(2): 93–110. doi:10.11646/phytotaxa.528.2.3 [Purpusii clade; abstract.]
  • 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 [Species accepted; relationship with Dioon merolae; treatments published on Plazi.]
  • 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 917. doi:10.5281/zenodo.6391973 [Pharaxonotha bicolor on Dioon califanoi, altitudes; treatments on Plazi.]
  • O’Brien, C.W. & Tang, W. (2015). Revision of the New World cycad weevils of the subtribe Allocorynina, with description of two new genera and three new subgenera (Coleoptera: Belidae: Oxycoryninae). Zootaxa 3970(1). doi:10.11646/zootaxa.3970.1.1 [Parallocorynus gregoryi on the Dioon argenteum–califanoi–purpusii complex; key on Plazi.]
  • Donaldson, J.S. (ed.) (2003). Cycads. Status survey and conservation action plan. IUCN, Gland and Cambridge. [Status in 2003 and numbers.]
  • Chemnick, J. & Gregory, T. (2022). Dioon califanoi. The IUCN Red List of Threatened Species 2022: e.T42145A69831286. doi:10.2305/IUCN.UK.2022-1.RLTS.T42145A69831286.en [Endangered; reference taken from The World List of Cycads and 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.]