Dioon nuusaviorum Mart.-Domínguez, Nic.-Mor. & D.W.Stev. is one of the most recently described species within the genus Dioon, a Mesoamerican cycad genus belonging to the family Zamiaceae. Formally published in May 2026 in the journal PhytoKeys, this species was discovered during fieldwork carried out in 2019 in the Mexican state of Guerrero. It remained unrecognized for years because populations were previously attributed to the closely related Dioon holmgrenii De Luca, Sabato & Vázq. Torres, despite originating from a geographically disjunct area. A combination of detailed morphological analysis — both vegetative and reproductive — and geographic data ultimately confirmed its status as a new, distinct species.
How to recognize Dioon nuusaviorum ?
Dioon nuusaviorum is a medium-sized cycad with an erect to decumbent stem that can reach up to 300 cm in length and 32 cm in diameter. The stem is covered by persistent leaf bases and may bifurcate in mature individuals. Cataphylls are persistent, coriaceous, linear to narrowly triangular, yellowish green, and densely light brown tomentose at emergence.
Each plant bears 20 to 50 leaves, drooping at maturity, ranging from 100 to 150 cm in length. Emerging leaves are light green — a feature that immediately distinguishes this species from the closely related Dioon stevensonii Nic.-Mor. & Vovides, whose new growth is golden brown. The petiole is subterete, 12–18 cm long, unarmed, densely light brown tomentose when young and glabrous at maturity.
The rachis carries 97 to 167 pairs of leaflets. These linear-lanceolate leaflets are one of the most diagnostic features of the species: they are imbricate to strongly imbricate (touching or overlapping each other on the rachis, with no gap between them), and their margin is distinctly curved acroscopically — that is, bent toward the upper face of the rachis. Median leaflets measure 6.8–12.3 cm long and 0.65–0.98 cm wide, and each bears 3 to 6 pronounced marginal denticles up to 0.37 cm long. Both the adaxial and abaxial surfaces are glabrous at maturity.
The pollen strobilus is solitary, ovoid when emerging, becoming angular-cylindrical at maturity, measuring 42–44 cm long and 8.2–8.5 cm in diameter. Microsporophylls are cuneiform, 3.4–3.8 × 1.5–2.0 cm, and terminate in an acuminate (tapering to a sharp point) apex — a character that separates Dioon nuusaviorum from both Dioon holmgrenii and Dioon stevensonii, whose microsporophylls have an acute apex.
The ovulate strobilus is solitary, ovoid, and erect, 45–56 cm long and 25–27.5 cm in diameter. Megasporophylls are strongly imbricate, 8.5–12 cm long and 4.8–5.4 cm wide, narrowly triangular, tomentose, and terminate in an apiculate (abruptly tipped) apex. The basal scales of megasporophylls are light green to yellowish green with an acute apex. Seeds are ovoid, 2.77–3.35 cm long, light brown at maturity, with a smooth sclerotesta bearing 13 to 15 radial ridge-like markings extending from the micropylar to the chalazal end.
Known hybrids
No natural or horticultural hybrids involving Dioon nuusaviorum have been documented to date. The species was only formally described in 2026, and its populations are confined to remote highland areas of Guerrero, where contact with other Dioon species is unlikely. No horticultural hybridization programs involving this species are known.
Confusion with other species
Dioon nuusaviorum most closely resembles Dioon holmgrenii and Dioon stevensonii, the two species with which it was compared in the original description.
From Dioon holmgrenii, it differs primarily by its imbricate to strongly imbricate leaflets (versus non-imbricate in Dioon holmgrenii, where leaflets are spaced 0.2–1.0 cm apart), by the acroscopic curvature of the leaflet margin (straight in Dioon holmgrenii), and by the greater number and length of marginal denticles (3–6 denticles of 0.26–0.37 cm versus 2–5 denticles of 0.15–0.29 cm). The apex of the microsporophylls is acuminate in Dioon nuusaviorum (acute in Dioon holmgrenii), and the megasporophylls are apiculate at the apex (acuminate in Dioon holmgrenii).
From Dioon stevensonii, it differs by the light green color of emerging leaves (golden brown in Dioon stevensonii), the strongly imbricate leaflets (non-imbricate in Dioon stevensonii), the tomentose indument and narrowly triangular shape of the megasporophylls (scarcely pubescent to glabrous and triangular in Dioon stevensonii), and the acuminate apex of the microsporophylls (acute in Dioon stevensonii).
In vegetative condition only, inexperienced observers might also confuse Dioon nuusaviorum with other species of the genus bearing overlapping or closely spaced leaflets, such as Dioon califanoi De Luca & Sabato, though the latter has strongly keeled leaves with leaflets inserted at an acute angle to the rachis, a character absent in Dioon nuusaviorum.
Taxonomy
Dioon nuusaviorum Mart.-Domínguez, Nic.-Mor. & D.W.Stev. was formally described in May 2026 by Lilí Martínez-Domínguez, Fernando Nicolalde-Morejón, Dennis Wm. Stevenson, Francisco G. Lorea-Hernández, and Francisco Vergara-Silva. The description was published in:
Martínez-Domínguez L, Nicolalde-Morejón F, Stevenson DWm, Lorea-Hernández FG, 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
The IPNI Life Sciences Identifier (LSID) for the name is: urn:lsid:ipni.org:names:77379798-1
The holotype specimen was collected on 28 May 2019 by F. Nicolalde-Morejón et al. (collection number 3156) near Rancho Viejo, municipality of Tlacoachistlahuaca, Guerrero, at 1,140 m elevation. It is deposited at the CIB herbarium (accession 22584UV), with an isotype at MEXU.
The name nuusaviorum derives from “Ñuu savi,” the endonym of the Mixtec people of Guerrero and Oaxaca, meaning “people of the rain” — “Ñuu savi” having come to replace “Mixtec” as the preferred designation for this ethnic group, since “Mixtec” is a Spanish adjustment of mixtecatl, the Nahuatl term for “cloud people.”
The genus Dioon belongs to the family Zamiaceae, subfamily Encephalartoideae, tribe Diooeae. It currently comprises 19 species (following the addition of Dioon nuusaviorum), all native to Mexico and Central America.
In the wild
Distribution
Dioon nuusaviorum is known only from three populations located in the Guerrero highlands district of the Sierra Madre del Sur, in southeastern Guerrero, Mexico. The localities cluster in the municipality of Tlacoachistlahuaca (near Rancho Viejo) and in the area of La Trinidad. The species has not been recorded from any other state. Its extent of occurrence (EOO) is estimated at approximately 11.7 km², and the area of occupancy (AOO) at approximately 12 km².
Habitat and ecology
The species inhabits pine forest and pine-oak forest formations at elevations between 1,030 and 1,190 m above sea level. The substrate consists of clay soils with scattered karstic rocks. The regional climate is temperate with a pronounced summer rainy season — consistent with the Guerrero highlands of the Sierra Madre del Sur, where orographic rainfall drives a marked wet-dry seasonality.
Each adult plant produces 12 to 18 new leaves annually, with leaf flush occurring in May. The phenological data collected during fieldwork indicate that pollen strobili are produced in the open-pollen phase from March to April, while ovulate strobili are in their late ovulate phase from May to June.
Dioon nuusaviorum coexists in its highland habitat with other cycad species characteristic of the Guerrero flora, notably Zamia paucijuga Wieland and, at lower elevations, Dioon stevensonii. As in all Dioon species, pollination is achieved through specialized insect vectors; related species in the same geographic area are associated with beetles of the genus Pharaxonotha (Coleoptera: Erotylidae) as obligate mutualistic pollinators.
Conservation status
Dioon nuusaviorum is preliminarily assessed as Endangered (EN) by the authors of the original description, applying IUCN criteria B1ab(ii, v) and C2a(i). The main threats are forest fires, which affect the pine-oak and pine forest ecosystems in which the species lives, and the expansion of the agricultural frontier into highland areas. Two of the three known populations occur in fire-disturbed areas; the third appears to be in better condition. Population sizes are relatively high given the species’ extreme geographic restriction, with good seedling and juvenile recruitment observed in the field.
As Dioon nuusaviorum was described in 2026, it is not yet included in the IUCN Red List as a formally evaluated taxon.
Cultivation
General notes
Dioon nuusaviorum is an extremely recently described species — its formal description was published in May 2026 — and there are currently no documented records of cultivation outside its natural habitat. No commercial specimens are known to be in circulation, and no horticultural data (substrate requirements, watering regimes, growth rates in cultivation, or response to container culture) have yet been published.
The general cultivation principles applicable to Dioon species from similar pine-oak forest habitats — particularly the closely related Dioon holmgrenii and Dioon stevensonii — may serve as a provisional reference. These species share a high-altitude origin (900–1,200 m), a temperate climate with seasonal drought, and clay soils over rocky substrate.
Outdoor / In-ground cultivation
Based on the ecological data from its native habitat (temperate highland climate, 1,030–1,190 m elevation, clay soils over karstic rock, strongly seasonal rainfall), Dioon nuusaviorum is expected to require well-drained substrate and good light exposure. Pine-oak forest species of Dioon typically tolerate moderate frost and brief cold spells far better than lowland species. However, no cultivation trials have been reported and no hardiness thresholds are known.
Container cultivation
Container cultivation is the most practical approach for most growers outside of warm subtropical or Mediterranean climates. In containers, Dioon species from highland habitats generally perform well in a free-draining, mineral-rich substrate — a mix of coarse grit, pumice, and loam is commonly used for related species. Given the absence of any cultivation data for Dioon nuusaviorum, all recommendations in this section remain provisional and should be treated with caution.
Propagation
Dioon nuusaviorum is a dioecious species: male and female cones are borne on separate individuals. Seed production therefore requires the simultaneous presence of flowering plants of both sexes, as well as appropriate pollinators or manual pollination.
Seeds are ovoid, 2.77–3.35 cm long, with a light brown sarcotesta at maturity. No germination protocols specific to this species have been published. By analogy with other Dioon species from humid highland habitats, seeds are best sown fresh in warm, moist conditions. Vegetative propagation through basal offsets has been reported in several related Dioon species, but the propensity of Dioon nuusaviorum to produce offsets in cultivation is unknown.
Pests and diseases
No pest or disease data specific to Dioon nuusaviorum are available. Cycads in cultivation are generally susceptible to cycad aulacaspis scale (Aulacaspis yasumatsui), a highly destructive armored scale insect that has devastated cycad collections worldwide. Systemic insecticide treatments and good air circulation are the primary preventive measures for this pest. Root rot caused by excessive soil moisture is the most common cultivation problem across the genus.
Hardiness
No cold hardiness data are available for Dioon nuusaviorum. Its native habitat at 1,030–1,190 m in the Guerrero highlands of the Sierra Madre del Sur experiences a temperate climate with occasional cold periods during the dry season (November–March). Minimum temperatures at these elevations can drop to near 5–8 °C on cold nights, though hard frosts are not regularly documented in this biogeographic district.
By comparison, Dioon holmgrenii, which occupies a similar pine-oak forest habitat in Oaxaca at comparable elevations, is generally rated for USDA zone 9b in cultivation (minimum −3.9 °C), with some tolerance of brief frost events when established. Dioon stevensonii, the other morphologically close species, is similarly considered suitable for zone 9b–10a.
Given the very recent formal description of Dioon nuusaviorum and the total absence of cultivation records, assigning a reliable USDA hardiness zone is not possible at this stage. Growers in zone 10 and above will likely be best positioned to trial this species outdoors; in cooler climates, frost protection or greenhouse cultivation should be planned.
FAQ
Is Dioon nuusaviorum available in the horticultural trade? Not as of 2026. The species was formally described in May 2026 and no commercial plants or seeds are known to be in circulation at present. Collectors and botanical gardens interested in this species should monitor future propagation programs at institutions involved in cycad conservation.
How does Dioon nuusaviorum differ from Dioon holmgrenii, which it most resembles? The most reliable distinguishing characters are the strongly imbricate leaflets (touching or overlapping one another) with acroscopically curved margins and 3–6 prominent denticles in Dioon nuusaviorum, versus non-imbricate leaflets with straight margins and 2–5 shorter denticles in Dioon holmgrenii. The apiculate apex of the megasporophylls in Dioon nuusaviorum (versus acuminate in Dioon holmgrenii) is a further diagnostic character, though it requires access to reproductive material.
Where exactly does Dioon nuusaviorum grow? It is known from three populations in the municipality of Tlacoachistlahuaca and the La Trinidad area of southeastern Guerrero, Mexico, in the Guerrero highlands district of the Sierra Madre del Sur, at elevations between 1,030 and 1,190 m.
Is Dioon nuusaviorum endangered? Based on the authors’ preliminary IUCN assessment at the time of description, yes: the species qualifies as Endangered under criteria B1ab(ii, v) and C2a(i), with a total estimated extent of occurrence of approximately 11.7 km². Threats include fire and agricultural encroachment on its pine-oak forest habitat.
Reference websites
PhytoKeys (Pensoft Publishers) — open-access journal hosting the original description: https://phytokeys.pensoft.net/article/173907/
IPNI (International Plant Names Index) — name record for Dioon nuusaviorum (LSID: urn:lsid:ipni.org:names:77379798-1): https://www.ipni.org/n/77379798-1
POWO (Plants of the World Online, Kew Science) — genus Dioon page: https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:331122-2
The World List of Cycads (cycadlist.org) — reference checklist for the genus Dioon: https://www.cycadlist.org
Bibliography
Martínez-Domínguez L, Nicolalde-Morejón F, Stevenson DWm, Lorea-Hernández FG, Vergara-Silva F (2026) A striking new species of Dioon (Zamiaceae) from pine and pine-oak forest of Guerrero, Mexico. PhytoKeys 274: 229–245. https://doi.org/10.3897/phytokeys.274.173907 [Original description of Dioon nuusaviorum.]
Nicolalde-Morejón F, Vovides AP, González-Astorga J, Stevenson DWm, Vergara-Silva F, Espinosa-Matías S (2014) A new arrangement in the cycad family Zamiaceae. Phytotaxa 190: 188–195. [General treatment of the genus Dioon.]
Calonje MA et al. (2025) The World List of Cycads. Published online at https://www.cycadlist.org [Updated checklist of cycad species worldwide.]
Gutiérrez-Ortega JS, Pérez-Farrera MA, Vovides AP et al. (2018a) The role of orogeny and aridification in the diversification of Dioon (Zamiaceae). Botanical Journal of the Linnean Society 186: 233–254. [Phylogeographic study of Dioon speciation in the Sierra Madre del Sur.]
Norstog KJ, Nicholls TJ (1997) The biology of the cycads. Cornell University Press, Ithaca. [Standard reference on cycad biology and ecology.]
Morrone JJ (2010) Fundamental biogeographic patterns across the Mexican Transition Zone: an evolutionary approach. Ecography 33: 355–361. [Biogeographic framework for the Guerrero highlands district.]