Dioon purpusii

Dioon purpusii is a cycad endemic to the dry canyons of northern Oaxaca, Mexico, around the Tomellín canyon and the Cañada de Cuicatlán, at middle elevations (roughly 900 to 1,750 m according to a 2020 revision). Described in 1909, this species of the genus Dioon forms a short trunk topped by stiff, moderately keeled leaves with spiny leaflets. Its name was long misapplied to other plants: Carl Purpus’s collections from Puebla, which became Dioon caputoi in 1980, and plants from Sonora reported under this name in the 1940s. It is listed as Endangered on the IUCN Red List, and plants sold under this name are often misidentified.

Key facts about Dioon purpusii

  • Accepted name: Dioon purpusii Rose (1909), 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 accepted synonym; the name Dioon edule var. purpusii, found in some databases, is considered invalid by the 2020 revision
  • Family: Zamiaceae, order Cycadales
  • Common names: no traditional English name; “fish bone cycad” is a nursery name; in Mexico “palma real” and several Chontal names (see Common names)
  • Natural range: Mexico, northern Oaxaca (Tomellín canyon, eastern branches of the Cañada de Cuicatlán); Puebla is cited by some sources but not by The World List of Cycads
  • IUCN status: Endangered (EN B1ab(v)), assessment by Bösenberg published in 2022; Vulnerable in the 2003 IUCN action plan
  • CITES and other protection: CITES Appendix II (annotation #4); Annex B in the European Union; “in danger of extinction” (P) under the Mexican standard NOM-059-SEMARNAT-2010, category kept in its 2019 update
  • Documented hardiness: no dated observation; a Californian nursery states “mid 20’s” °F, about −4 °C (25 °F) (see Cold hardiness)
  • Light and soil: in the wild, a deep canyon shaded by shrubs and small trees (type locality), between dry tropical forest and oak woodland; in cultivation, sun or part sun according to a specialist nursery; soil not documented
  • Habit and adult size: short trunk 25 to 40 cm across, plants 1.5 to 2 m tall; leaves 80 to 160 cm long
  • In the UK, US and Australia: Kew (BGCI); Montgomery Botanical Center (eight accessions, 2001 to 2019), Fairchild and some twenty other American gardens; Royal Botanic Gardens Victoria (BGCI)
  • Toxicity: no data for the species; toxins documented in other cycads (see Toxicity and precautions)

How to recognise Dioon purpusii

Dioon purpusii is recognised by its moderately keeled leaves, which form an open V, its glossy, spiny leaflets that overlap little or not at all, and the down on young leaves, which is soon shed. Joseph Nelson Rose’s original description (1909), read on the Internet Archive, is brief: a short trunk crowned by many stiff, erect leaves, often a metre long or more; leaflets 5 to 9 cm long, rigid and pungent, 1 to 1.5 cm apart towards the base of the leaf and crowded higher up, entire on the lower margin and usually bearing one or two spines, rarely three, on the upper margin; male cones 15 to 20 cm long; female cones oval, 44 by 20 cm, with very woolly scales; seeds about 4 cm long.

The revision by Hernández-Tapia and co-authors (2020), several points of which were disputed by Haynes (2020), adds:

  • Habit: plants 1.5 to 2 m tall, with a short trunk 25 to 40 cm in diameter;
  • Leaves: 8 to 25 in the crown, 80 to 160 cm long; petiole 10.5 to 31 cm, woolly at the base;
  • Leaflets: 75 to 130 pairs, linear-lanceolate, ascending, slightly overlapping, with entire margins or two or three spines; the lowest reduced to spines (pinnacanths);
  • Male cones: cylindrical, 20 to 36 cm long and 7 to 13 cm wide;
  • Female cones: ovoid, 44 to 52.5 cm long and 20 to 25 cm wide;
  • Seeds: almost spherical, 3 to 4 cm, with a yellow sarcotesta.

The most debated character is the keel of the leaf. Chemnick, Gregory and Salas-Morales (1997), after visiting the type locality and three other populations, wrote that adult leaves are rarely flat but moderately to strongly keeled, the leaflets raised 20 to 45° above the rachis in young and adult plants alike. Gregory and co-authors (2003) measured an average angle of 122° between the two rows of leaflets, against 164° in Dioon argenteum and 80° in Dioon califanoi.

Hybrids

No hybrid of Dioon purpusii has been reported.

Possible confusion

Dioon purpusii is one of the most frequently misidentified Dioon. Chemnick, Gregory and Salas-Morales (1997) note that many plants grown under this name are in fact Dioon merolae, Dioon holmgrenii, Dioon caputoi, Dioon sonorense or Dioon tomasellii, especially when their leaves are flat or their leaflets bent downwards. Conversely, a Dioon with keeled leaves and spiny leaflets has a good chance of being Dioon purpusii, although Dioon califanoi can look much the same.

Within the Dioon purpusii complex defined in 2003, Dioon califanoi differs in more strongly keeled leaves and glaucous, almost spineless leaflets once the down has gone; Dioon argenteum in almost flat leaves and a silvery down that persists for more than a year. The key of Martínez-Domínguez and co-authors (2026) also separates Dioon purpusii from Dioon planifolium by the petiole base, woolly at maturity, and by the straight tip of the male cone scales. Dioon caputoi has flat leaves and regularly spaced leaflets 4 to 5 mm wide.

Taxonomy

Dioon purpusii is an accepted name. Joseph Nelson Rose described it in 1909 in the Contributions from the United States National Herbarium (12: 260–261). The type was collected on 7 September 1906 in the Tomellín canyon, Oaxaca, by Daniel T. MacDougal and Rose (Rose 11352; holotype at the United States National Herbarium, US 454142). The World List of Cycads gives the collectors as J.N. Rose and J.S. Rose, whereas the original description and the 2020 revision name MacDougal and Rose.

Rose attached to his species the seeds and cone scales collected in 1908 by Carl Albert Purpus in the Sierra Mixteca of Puebla. These collections, and others made by Purpus in 1907, were distributed to many herbaria as Dioon purpusii, and J. Schuster relied mainly on them for his 1932 description. Botanists of the University of Naples took up the problem in the 1970s: Sabato, La Valva and Moretti first discussed the “new taxa” wrongly attributed to the species in 1976–1977, from the literature; in 1979 De Luca, Sabato and Vázquez Torres published a new description of Dioon purpusii in the journal Delpinoa, and in 1980 they showed that Purpus’s collections belonged to another species, which they named Dioon caputoi. Chemnick and co-authors (1997) later corrected the statement of the 1979 description that adult leaves are flat.

The name was also applied to plants from Sonora. The Gymnosperm Database reproduces the observations of Howard Scott Gentry, published in 1942 in his flora of the Río Mayo, on a “Dioon purpusii” from Sonora; those plants, far from Oaxaca, do not match the species as now delimited, and the information derived from them (local names “palma de la Virgen” and “palmita”, medicinal use of the seeds, altitudes of 450 to 900 m) does not apply to it.

Gregory and co-authors (2003) grouped Dioon purpusii, Dioon califanoi and Dioon argenteum in a “Dioon purpusii complex” of recently diverged species. Gutiérrez-Ortega and co-authors (2021) place the species in a wider group, the “Purpusii clade”, which also includes Dioon caputoi, Dioon planifolium, Dioon holmgrenii, Dioon merolae, Dioon oaxacensis and Dioon salas-moralesiae.

Etymology and history

The epithet purpusii honours Carl Albert Purpus, one of the leading plant collectors in Mexico in the early twentieth century, who collected seeds attributed to the species in 1908. The Harvard Index of Botanists names him Carl (Karl) Albert Purpus and gives the dates 1851–1941; The World List of Cycads, following Haynes (2022), writes “Carl Anton Purpus (1853–1914)”. The Purpus collections behind the dedication belong, for the most part, to Dioon caputoi.

Rose reports that the 1906 collection was made in a deep canyon, well shaded by shrubs and small trees. Male and female cones were brought back, together with a living plant later grown in the glasshouse of the New York Botanical Garden: the first documented introduction into cultivation. In 1979, the Naples botanists Aldo Moretti and Sergio Sabato, with a student of the Universidad Veracruzana, travelled by train to the Tomellín canyon, in a landscape dominated by the candelabra cactus Pachycereus weberi, to check in the field what had until then been described from the literature alone (Moretti’s account, published in 2022). In 1997, Chemnick and co-authors credited the discovery of previously unknown populations to the fieldwork of Silvia Salas-Morales.

Common names

No traditional English name is attested. The Californian nursery Jungle Music calls it the “fish bone cycad”, after the look of its regularly spaced leaflets; this is a trade name. In Spanish, Species+ gives “palma real”, and the Enciclovida database of CONABIO cites “palma real de Tomellín”, “palma real” and “chamal”. The 2019 update of the Mexican standard NOM-059-SEMARNAT-2010 lists “palma real” and four Chontal names, “la-fane-tejuá”, “lan-dzi-le”, “lan-zi-lé” and “lan-zi-lí”, the transcriptions also cited by Enciclovida after the compendium of Bonta and Osborne (2007). “Palma real” and “chamal” are also used for other Dioon.

In the wild

Dioon purpusii grows in the canyons of northern Oaxaca whose rivers join the Río Santo Domingo, flowing towards the Gulf of Mexico: the Tomellín canyon, around Santa Catarina, and the eastern branches of the Cañada de Cuicatlán. In 1997, Chemnick and co-authors knew of three populations in the basins of the Río La Hondura and the Río Santo Domingo besides the type locality; Gregory and co-authors counted five in 2003. According to the latter, the species occupies, like its close relatives, the transition zone between dry tropical forest and oak-pine forest. The 2020 revision cites xerophytic scrub, oak woodland and dry tropical forest between 900 and 1,750 m; some of the specimens it lists, at very different altitudes, appear doubtful.

The World List of Cycads gives Oaxaca only. The 2020 revision also cites Puebla, and Kew’s World Checklist of Vascular Plants records the species in central Mexico, the region that includes Puebla, as well as in the south-west; but part of the old Puebla records rests on Purpus’s collections, now assigned to Dioon caputoi.

The male cones host the small pollen-eating beetle Pharaxonotha bicolor, collected at Santa Catarina at about 1,400 m in November 2012, together with two weevils, Parallocorynus gregoryi and Parallocorynus chemnicki (Skelley and co-authors, 2022). Their role in pollinating the species has not been demonstrated.

Conservation status and regulation

Dioon purpusii is listed as Endangered (EN) on the IUCN Red List under criteria B1ab(v), in an assessment by J.D. Bösenberg dated 4 July 2020 and published in 2022 (The World List of Cycads, GBIF, Crossref): a small extent of occurrence, few or fragmented populations and a continuing decline in the number of mature individuals. The IUCN cycad action plan (Donaldson, 2003) listed it as Vulnerable, with 2,500 to 3,000 plants, a moderate decline, habitat destruction and collecting as threats, and presence in a protected area.

Like all Dioon, the species is listed in CITES Appendix II, with annotation #4, which exempts seeds in particular, and in Annex B of the European regulation (Regulation (EU) 2026/1383, in force since 29 June 2026), according to Species+. In Mexico it is classed as “en peligro de extinción” (P) in the NOM-059-SEMARNAT-2010 list of 2010, a category kept in the 2019 update. Plants sold abroad must come from cultivation and carry the required documents. Databases checked on 26 October 2026: check the regulations in force.

Growing Dioon purpusii

Few published sources describe the cultivation of Dioon purpusii. The San Diego nursery Jungle Music describes it as a sun plant that tolerates partial sun, slow-growing and rare in cultivation. The Tenerife nursery Canarius offered in 2026 a plant of almost ten years with a base 11 cm in diameter, which gives an idea of its slow growth, and lists it as a sun plant needing protection. In the absence of data specific to the species, a mineral, free-draining mix and moderate watering remain the usual precautions for a Dioon of dry forest.

At Nong Nooch Tropical Botanical Garden, in Thailand, all described Dioon are planted in the ground and the species of the genus seem to adapt to excessive rain and humidity (Lindstrom, 2022); the article gives no detail specific to Dioon purpusii. Before buying, check the identity of the plant: according to Chemnick and co-authors (1997), mislabelled plants are common in cultivation.

Outdoor and in-ground cultivation

No dated outdoor planting has been described for the species, in California, Florida, Australia or the Mediterranean. No observation of Dioon purpusii has been published for the Jardin zoologique tropical at La Londe-les-Maures, in the Var.

Container cultivation

The Jungle Music plant shown in 2024 was grown in a container, with a caudex of 3 inches (about 8 cm). In climates with frost, a pot with a mineral mix, kept frost-free and dry in winter, is the prudent option.

In cultivation in the UK, US and Australia

  • United Kingdom: the Royal Botanic Gardens, Kew, declares the species to BGCI PlantSearch; no outdoor cultivation is documented in Britain.
  • United States: the Montgomery Botanical Center (Coral Gables, Florida) lists eight accessions in its online catalogue, three from 2001, one from 2003, one from 2018 and two from 2019; the Fairchild Tropical Botanic Garden (Miami) listed it in its online catalogue in October 2026. BGCI PlantSearch also lists Lotusland, the Huntington, Descanso Gardens, the San Diego Zoo, SeaWorld San Diego, the University of California Botanical Garden at Berkeley, the Desert Botanical Garden (Phoenix), Denver Botanic Gardens, Longwood Gardens, the New York Botanical Garden, Marie Selby Botanical Gardens, Naples Botanical Garden, the Edison and Ford Winter Estates, Moore Farms Botanical Garden (South Carolina), the John Fairey Garden (Texas), three Hawaiian gardens and the US National Plant Germplasm System. A BGCI listing is a declaration by the garden, not proof that the plant is alive today, and given the frequency of misidentifications, not every plant under this name is necessarily the true species.
  • Australia: Royal Botanic Gardens Victoria (Melbourne) declares the species to BGCI; no other Australian record has been found.

Propagation

Propagation is by seed. Seeds are rare: in March 2013, a grower on the French Fous de palmiers forum noted their offer by a specialist seed merchant as an unusual event. Nothing specific to the species has been published on germination or on the removal of offsets.

Pests and diseases

No disease or pest specific to Dioon purpusii is documented in cultivation. In the wild its male cones host specialised beetles and weevils, with no described effect on the plant. In cultivation, the risks reported for cycads in general still apply: root rot in a mix that stays wet, and scale insects.

Cold hardiness

No dated observation of the cold tolerance of Dioon purpusii has been published. The values available are estimates from nurseries and growers.

Mediterranean and European experience

No cultivation report of Dioon purpusii, in the ground or in a pot, is documented in France. On the Fous de palmiers forum, a grower whose profile gives Belley (Ain) and Montpellier (Hérault) estimated in May 2021 that the Dioon close to Dioon holmgrenii, such as Dioon merolae or Dioon purpusii, may suffer leaf damage at around −4 to −5 °C (25 to 23 °F), and that repeated defoliation weakens the plant; he cited no observation of this species.

United Kingdom, United States and Australia

  • Nursery claims: Jungle Music (San Diego, California) states that it is hardy “down to the mid 20’s”, i.e. about −4 °C (25 °F); the Canarius nursery (Tenerife) puts it in its “−5 °C to 0 °C” (23 to 32 °F) minimum winter temperature class. Neither gives a place, a duration of cold or the age of the plants; these are commercial assessments.
  • No dated report from a British, American or Australian grower has been found, and the gardens that grow it have published no cold data.

Toxicity and precautions

No toxicity data have been published for Dioon purpusii. The medicinal use of the seeds sometimes attributed to the species comes from Gentry’s observations in Sonora, which concerned another plant. The risk is documented in other cycads, which contain toxic glycosides (cycasin, macrozamin), from which methylazoxymethanol is derived, a toxin affecting the liver and the nervous system, dangerous to people, livestock and pets. Treat the species as potentially toxic and keep the seeds out of reach of children and animals. If any part has been eaten, contact a poison centre, a doctor or a vet.

Traditional uses

The 2020 revision mentions only ornamental use. Chemnick and co-authors (1997) describe a widespread use of Dioon leaves in Oaxaca to decorate windows, doors and religious statues during festivals, especially at Easter, without specifying the species involved. The use of the leaves on Palm Sunday, sometimes cited for Dioon purpusii, has not been confirmed by a verifiable source.

Frequently asked questions

How can Dioon purpusii be recognised?

By its moderately keeled leaves and spiny leaflets. The leaves form an open V, the leaflets are glossy, overlap little or not at all and usually carry one to three spines on the upper margin. The down on young leaves is soon shed.

What is the difference from Dioon califanoi?

Mainly the keel and the spines. Dioon califanoi has more strongly keeled leaves and glaucous, almost spineless leaflets; Dioon purpusii has a more open keel and glossy, spiny leaflets. The two can nevertheless look alike.

Are plants sold under this name reliable?

Not always. According to the specialists who studied the species in the field, misidentified plants are common in cultivation. A plant with flat leaves or leaflets bent downwards is probably another species.

Is Dioon purpusii hardy?

Not reliably, as far as is known. No dated trial has been published; nurseries claim about −4 °C (25 °F), without detail. Outside frost-free climates, grow it in a pot kept frost-free and dry in winter.

Why is the name Dioon purpusii confusing?

Because it long covered other plants. Purpus’s collections from Puebla became Dioon caputoi in 1980, and plants from Sonora were reported under this name in 1942. Information drawn from those sources does not concern the species.

Is it endangered?

Yes. The IUCN lists it as Endangered, it is in CITES Appendix II and it is protected in Mexico. Its few populations lie in a handful of canyons in northern Oaxaca.

Further reading on Succulentes

Sources

Reference sites

Bibliography

  • Rose, J.N. (1909). Cycadaceae. A new species of Dioon. In: Studies of Mexican and Central American plants. Contributions from the United States National Herbarium 12(7): 260–261. [Protologue; full text (archive.org).]
  • Sabato, S., La Valva, V. & Moretti, A. (1976–1977). Dioon purpusii Rose e nuovi “taxa” erroneamente attribuiti a questa specie. Delpinoa 18–19: 107–116. [Misattributions to the species; cited from Moretti (2022).]
  • De Luca, P., Sabato, S. & Vázquez Torres, M. (1979). Dioon purpusii Rose, a misknown species of Zamiaceae. Delpinoa n.s. 20: 31–35. [New description of the species; cited from later literature.]
  • De Luca, P., Sabato, S. & Vázquez Torres, M. (1980). Dioon caputoi (Zamiaceae), a new species from Mexico. Brittonia 32(1): 43–46. doi:10.2307/2806216 [Separation of Dioon caputoi; full text.]
  • Chemnick, J., Gregory, T.J. & Salas-Morales, S. (1997). A revision of Dioon tomasellii (Zamiaceae) from western Mexico, a range extension of Dioon merolae, and clarification of Dioon purpusii. Phytologia 83(1): 1–6. [Leaf keel, populations, misidentifications; full text (archive.org).]
  • Donaldson, J.S. (ed.) (2003). Cycads. Status Survey and Conservation Action Plan. IUCN/SSC Cycad Specialist Group, Gland and Cambridge. [VU status and estimated numbers (table 6.1); full text.]
  • Gregory, T.J., Chemnick, J., Salas-Morales, S. & 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, keel angle, number of populations; full text.]
  • Bonta, M. & Osborne, R. (2007). Cycads in the vernacular: a compendium of local names. Memoirs of the New York Botanical Garden 97: 143–175. doi:10.21135/893274900.010 [Local names, as cited by Enciclovida and the 2020 revision.]
  • 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, habitat, common names; treatment of the species (Plazi). Revision criticised by Haynes (2020).]
  • Haynes, J.L. (2020). Review of “Taxonomic revision of the genus Dioon (Zamiaceae)”. Phytotaxa 471(1): 69–89. doi:10.11646/phytotaxa.471.1.8 [Critique of the 2020 revision; abstract.]
  • 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 and key (Plazi).]
  • Skelley, P.E., Tang, W. & Pérez-Farrera, M.A. (2022). Review of Pharaxonotha Reitter inhabiting the cycad genus Dioon Lindl., with descriptions of nine new species. Insecta Mundi 0908: 1–21. [Insects of the male cones; open-access article.]
  • Bösenberg, J.D. (2022). Dioon purpusii. The IUCN Red List of Threatened Species 2022: e.T42147A69830671. doi:10.2305/IUCN.UK.2022-1.RLTS.T42147A69830671.en [Category EN B1ab(v); reference checked on Crossref and The World List of Cycads.]
  • Haynes, J.L. (2022). Etymological compendium of cycad names. Phytotaxa 550(1): 1–31. doi:10.11646/phytotaxa.550.1.1 [Dedicatee, as given by The World List of Cycads.]
  • Lindstrom, A. (2022). The cycad collection at Nong Nooch Tropical Botanical Garden, Thailand. CYCADS 6(1). [Cultivation of Dioon in a tropical climate.]
  • Martínez-Domínguez, L., Nicolalde-Morejón, F., Stevenson, D.W., Lorea-Hernández, F.G. & Vergara-Silva, F. (2026). A striking new species of Dioon (Zamiaceae) from pine and pine-oak forest of Guerrero, Mexico. PhytoKeys 274: 229–245. doi:10.3897/phytokeys.274.173907 [Key including Dioon purpusii.]
  • 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.]