Dioon nuusaviorum

Dioon nuusaviorum is a trunk-forming cycad endemic to south-eastern Guerrero, Mexico, where it grows in pine and pine-oak forest at 1,030 to 1,190 m (3,380 to 3,900 ft) in the Sierra Madre del Sur. The most recently described species of the genus Dioon, it was published in May 2026 in the journal PhytoKeys, from populations found in 2019. Its crowded, overlapping leaflets, curving towards the tip of the leaf and armed with long teeth, and its light green new leaves set it apart from its neighbours. Its describers consider it Endangered; it has not yet been assessed by the IUCN, and it is not known in cultivation.

Key facts about Dioon nuusaviorum

  • Accepted name: Dioon nuusaviorum Mart.-Domínguez, Nic.-Mor. & D.W.Stev. (2026), accepted by The World List of Cycads (version 2026.08.15) and registered by IPNI; not yet included in the June 2026 version of Kew’s World Checklist of Vascular Plants, the database behind POWO (published on GBIF)
  • Former names and synonyms: none; the populations had earlier been considered similar to Dioon holmgrenii
  • Family: Zamiaceae, order Cycadales
  • Common names: none attested
  • Natural range: Mexico, south-eastern Guerrero (Sierra Madre del Sur), three known populations
  • IUCN status: Not Evaluated (NE); preliminary assessment as Endangered (EN) proposed by the authors of the species
  • CITES and other protection: CITES Appendix II, through the listing of all cycads (annotation #4: seeds exempt); Annex B in the European Union
  • Documented hardiness: no data (see Cold hardiness)
  • Light and soil: not documented in cultivation; in the wild, clay soils with scattered karstic rocks, in pine-oak forest
  • Habit and adult size: trunk upright to reclining, up to 3 m long and 32 cm (13 in) across, sometimes forked; 20 to 50 leaves 1 to 1.5 m long
  • In the UK, US and Australia: no garden declares the species to BGCI, and the Montgomery Botanical Center catalogue does not list it
  • Toxicity: no analysis for the species; toxins documented in other cycads (see Toxicity and precautions)

How to recognise Dioon nuusaviorum

Dioon nuusaviorum is recognised by its overlapping to strongly overlapping leaflets, whose margin curves towards the tip of the leaf, by their three to six long marginal teeth and by its light green new leaves. The original description (Martínez-Domínguez and co-authors, 2026), an open-access article, gives the following characters:

  • Trunk: above ground, upright to reclining, up to 3 m long and 32 cm across, covered with old leaf bases, sometimes forked in old plants.
  • Cataphylls: persistent, leathery, linear to narrowly triangular, yellowish green, 9 to 13 cm long, densely covered in light brown down when they emerge.
  • Leaves: 20 to 50, 100 to 150 cm long, described as “dropping at maturity” (probably drooping), light green at emergence with a brown down that turns greyish brown and then disappears; petiole almost cylindrical, 12 to 18 cm, without spines.
  • Leaflets: 97 to 167 pairs, linear-lanceolate, leathery, flat, inserted at right angles on the axis, overlapping to strongly overlapping, with the margin curved towards the leaf tip; middle leaflets 6.8 to 12.3 cm long and 0.65 to 0.98 cm wide; up to four teeth on the outer margin and one or two on the inner one, 0.26 to 0.37 cm long.
  • Male cones: solitary, ovoid at first then angular-cylindrical, 42 to 44 cm long and 8.2 to 8.5 cm across, with a fine light brown down; scales wedge-shaped, 3.4 to 3.8 cm, ending in a tapering (acuminate) point.
  • Female cones: solitary, ovoid, upright, 45 to 56 cm long and 25 to 27.5 cm across; scales 8.5 to 12 cm by 4.8 to 5.4 cm, strongly overlapping, narrowly triangular, green and woolly, ending in a short point (apiculate).
  • Seeds: ovoid, 2.77 to 3.35 cm by 1.99 to 2.31 cm, light brown when ripe, with a pale yellow fleshy coat; the stony inner shell is smooth, with 13 to 15 radiating ridges.

The authors stress that leaf characters are often enough, but that the shape of the cone scales gives the safest identification, each of the neighbouring species having its own combination of characters.

Hybrids

No natural or garden hybrid of Dioon nuusaviorum has been reported. The 2026 description mentions no other Dioon growing with its populations: Dioon stevensonii, its nearest geographical neighbour, is distributed along the Pacific coastal region, and the two species are not recorded together.

Possible confusion

The two species closest in appearance are Dioon holmgrenii, from Oaxaca, and Dioon stevensonii, from Guerrero and Michoacán. The 2026 description compares them point by point:

  • Dioon holmgrenii: leaflets not overlapping (generally 0.2 to 1 cm apart), with straight margins and two to five short teeth (0.15 to 0.29 cm); male cone scales with an acute tip, female cone scales with a tapering tip.
  • Dioon stevensonii: new leaves golden brown (not light green), leaflets not overlapping according to the text, male cone scales with an acute tip, female cone scales triangular, slightly or barely hairy.

The key published in the same article also separates the species with keeled leaves and leaflets inserted at an acute angle on the axis, such as Dioon califanoi, whose leaflets also overlap, Dioon argenteum, Dioon purpusii and Dioon planifolium; Dioon nuusaviorum has flat leaves with leaflets set at right angles. Among the flat-leaved species, Dioon caputoi, Dioon salas-moralesiae and Dioon oaxacensis have leaflets that do not overlap. In the same key, Dioon stevensonii is placed among species with overlapping leaflets, which contradicts the text and the comparison of the article; this page follows the text.

Taxonomy

Dioon nuusaviorum is accepted by The World List of Cycads and registered by IPNI. Described in May 2026, it does not yet appear in the June 2026 version of Kew’s World Checklist of Vascular Plants, the database behind POWO, published on GBIF. The species was described by Lilí Martínez-Domínguez, Fernando Nicolalde-Morejón and Dennis Wm. Stevenson, in a paper co-authored with Francisco G. Lorea-Hernández and Francisco Vergara-Silva, published on 11 May 2026 in PhytoKeys (volume 274, pages 229 to 245; description on page 235).

The type was collected on 28 May 2019 near Rancho Viejo, in the municipality of Tlacoachistlahuaca (Guerrero), at 1,140 m, by Fernando Nicolalde-Morejón and colleagues (number 3156). The holotype is kept in the CIB herbarium of the Universidad Veracruzana, with an isotype at MEXU (Mexico City). Other specimens were collected the same day near Rancho Viejo, at about 1,190 m, and at La Trinidad, at about 1,030 m.

The authors found these populations in 2019, while studying another cycad in Guerrero, Ceratozamia leptoceras. They had been considered morphologically similar to Dioon holmgrenii, a species of Oaxaca with a clearly separate range. After examining herbarium specimens of all the species of the genus and observing populations in Oaxaca, the authors described them as a new species. Their approach is morphological: ten to fifteen plants per population, one matrix of 24 qualitative characters and another of 37 measured characters, analysed by population aggregation analysis, analyses of variance and principal component analysis. The three species separate clearly, without overlap.

No genetic data were produced. The authors suggest that Dioon nuusaviorum may be the sister species of Dioon stevensonii, adding that molecular data are needed to test this. With it, the genus has nineteen species, eighteen of them in Mexico, and Guerrero now has four known cycads, with Ceratozamia leptoceras, Dioon stevensonii and Zamia paucijuga.

Etymology and history

The epithet honours the Ñuu savi people, the name the Mixtec people use for themselves, which translates as “people of the rain” (The World List of Cycads, after the original description). According to the authors, “Ñuu savi” is replacing “Mixtec”, a Spanish adaptation of mixtecatl, the Nahuatl name meaning “cloud people”. They also thank Ñuu savi collaborators for their help in the field. The genus name comes from the Greek dis, “two”, and ôon, “egg”, after the two seeds borne by each scale of the female cone.

The species has no known horticultural history: no introduction into cultivation has been documented since its description.

Common names

No common name is attested for Dioon nuusaviorum, in English, Spanish or Mixtec. The original description gives none.

In the wild

Dioon nuusaviorum is known only from three populations in the Guerrero highlands district of the Sierra Madre del Sur, in the south-east of the state: around Rancho Viejo (municipality of Tlacoachistlahuaca) and at La Trinidad. The authors found no earlier record of Dioon from south-eastern Guerrero, either in herbaria or in the floristic inventories of the region.

It grows in pine forest and pine-oak forest between 1,030 and 1,190 m, on clay soils with scattered karstic rocks. The authors describe the climate of the region as temperate, with a pronounced summer rainy season; no climate figures have been published for its localities. Each population has more than 50 adult plants, and the authors observed good recruitment of seedlings and young plants.

New leaves appear each year in May, 12 to 18 per adult plant on average, sometimes only 9 or 10. The male cones shed pollen in March and April; female cones were seen at the end of their receptive phase in May and June. Pollinators have not been identified; a figure in the article shows a butterfly of the genus Eumaeus photographed in the habitat, without comment from the authors.

Conservation status and regulation

Dioon nuusaviorum has not yet been assessed by the IUCN: The World List of Cycads lists it as Not Evaluated (NE). Its describers propose, as a preliminary assessment, the category Endangered (EN), under criteria B1ab(ii,v) and C2a(i), calculated with the GeoCAT tool. They give an extent of occurrence of “11.662 km²” and an area of occupancy of “12.000 km²”; the use of a point makes it impossible to tell whether these mean about 11.7 and 12 km² or thousands of square kilometres.

The threats cited are fire, frequent in pine-oak forest, and the advance of farmland. Two of the three populations lie in fire-affected areas; the third, less exposed, appears to be in better condition.

The species falls under CITES Appendix II through the listing of all cycads since 1977; Species+ has no record under its name yet (checked on 26 October 2026). Annotation #4, in its version of 5 March 2026, exempts seeds, pollen, in vitro cultures in sterile containers and cut flowers. In the European Union it falls under Annex B (Regulation (EU) 2026/1383, in force since 29 June 2026). Described in 2026, it does not appear in the Mexican standard NOM-059-SEMARNAT-2010. Check the regulations in force before any purchase or import.

Growing Dioon nuusaviorum

No cultivation data exist for Dioon nuusaviorum: no garden collection, forum or nursery mentions it. Advice drawn from neighbouring species has not been tested on it. Its habitat, pine-oak forest in the mountains on clay and limestone rocks, with a dry season, suggests a plant for free-draining soil and bright light, but that is only a deduction.

Outdoor and in-ground cultivation

No in-ground trial has been documented anywhere. The Jardin zoologique tropical at La Londe-les-Maures has published no observation of the species, and no Mediterranean experience is available.

Container cultivation

No container trial has been published. Should seed-grown plants become available, a pot with a free-draining mineral mix, kept frost-free until the species’ limits are known, would be the prudent approach.

In cultivation in the UK, US and Australia

  • United Kingdom: no garden declares the species to BGCI PlantSearch.
  • United States: no garden declares it to BGCI, and the online catalogue of the Montgomery Botanical Center does not list it (October 2026).
  • Australia: no garden declares it to BGCI.

Propagation

No propagation data specific to the species have been published. Like all Dioon, it has separate male and female plants, and seed is the normal route; in Dioon, the female cone can take up to two years from its appearance to the release of the seeds (Norstog and Nicholls, 1997, cited by the authors). Seeds are exempt from CITES permits; given the status of the species, only seeds from cultivated plants would be acceptable.

Pests and diseases

No disease or pest is documented for Dioon nuusaviorum. In the wild, the main threat is fire, which affects two of the three known populations.

Cold hardiness

The cold hardiness of Dioon nuusaviorum is unknown: no measurement, no cultivation report and no published climate data for its localities (minimum temperatures, frost frequency) exist. The only information is that its describers call the climate of its range temperate.

Mediterranean and European experience

No trial is documented in Europe, either in the ground or in a pot. No plant is known to be in cultivation there.

United Kingdom, United States and Australia

No report exists. Any hardiness value or USDA zone that may circulate for this species would be an estimate without observation behind it.

Toxicity and precautions

No toxicity analysis has been published for Dioon nuusaviorum, but it should be treated as toxic. Cycads contain toxic glycosides (cycasin, macrozamin), from which methylazoxymethanol is derived, a toxin affecting the liver and the nervous system. The risk is documented mainly in other cycads, for dogs that chew the seeds and for livestock. Wear gloves to handle the seeds and keep them 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 use is documented for Dioon nuusaviorum; the original description mentions none.

Frequently asked questions

When was Dioon nuusaviorum described?

On 11 May 2026, in the journal PhytoKeys. The populations had been found in 2019 in Guerrero; it is the nineteenth species of the genus.

How can it be told from Dioon holmgrenii?

Mainly by the leaflets. Those of Dioon nuusaviorum overlap, have a margin curved towards the leaf tip and three to six long teeth; those of Dioon holmgrenii are spaced and straight, with shorter teeth. The cone scales confirm the identification.

And from Dioon stevensonii?

By the colour of the new leaves. They emerge light green in Dioon nuusaviorum and covered in golden-brown down in Dioon stevensonii; the leaflets and cone scales also differ.

What does its name mean?

It honours the Ñuu savi people, the name the Mixtec people use for themselves, meaning “people of the rain”.

Is it endangered?

Probably. The IUCN has not yet assessed it, but its describers propose the category Endangered: there are only three populations, threatened by fire and farming.

Can it be grown?

Not for now. No plants or seeds are documented for sale, and there are no cultivation or hardiness data.

Is it toxic?

Yes, as a precaution. No analysis exists for the species, but the cycads studied contain dangerous toxins, especially in the seeds.

Further reading on Succulentes

Sources

Reference sites

Bibliography

  • 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 [Protologue; open-access peer-reviewed article.]
  • Norstog, K.J. & Nicholls, T.J. (1997). The Biology of the Cycads. Cornell University Press, Ithaca. [Development time of female cones; cited from the protologue.]
  • 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.]