Every other Dioon species in this encyclopedia is Mexican. Dioon mejiae is the exception — and what an exception it is. This is the only species in the genus that occurs outside Mexico, endemic to the mountains of northeastern Honduras, where it is known by a name — tiusinte — that carries the weight of a centuries-old food culture. An estimated 33,000 indigenous and mestizo Hondurans still depend on Dioon mejiae as a seasonal wild food that supplements their maize-and-bean diet. Female cones weighing up to 23 kg are harvested, seeds are detoxified and ground into flour, and the resulting pan de tiusinte — cycad bread — is consumed as tamales, tortillas, and porridge during the lean season before the corn harvest. This is one of the few cycads on Earth that remains a genuine dietary staple for a large human population — a living parallel to the Aboriginal Australian cycad food cultures. The plant itself is spectacular: among the largest and most abundant cycads in the New World, reaching 7 m or more in height, with sweeping crowns of 1–2 m long leaves. The Saguay tiusintal in Gualaco, Olancho, once contained over 300,000 adult plants — a population size virtually unprecedented in the cycad world. Yet this abundance is rapidly declining under the pressure of timber extraction, cattle ranching, and slash-and-burn agriculture.
Quick Facts
| Scientific name | Dioon mejiae Standl. & L.O.Williams |
| Family | Zamiaceae |
| Origin | Honduras — departments of Olancho, Colón, and Yoro (northeastern Honduras); possibly Nicaragua |
| Adult size | Trunk to 7+ m tall, 17–36 cm diameter; crown spread 2–3 m |
| Hardiness | ~0 to −2 °C (32 to 28 °F) / USDA zones 10a–11 (essentially frost-free) |
| IUCN | Vulnerable (VU) |
| CITES | Appendix II (all Dioon species) |
| Cultivation difficulty | 3/5 |
Taxonomy and Nomenclature
Dioon mejiae was described by Paul Carpenter Standley and Louis Otto Williams in 1950 in Ceiba (1: 36–38), based on cultivated plants collected in the departments of Francisco Morazán, El Paraíso, and Olancho, Honduras. The species had been known locally for centuries under the name “tiusinte” (also spelled teocinte, teosinte, teocsinte, teocintle), but twentieth-century Honduran botanists had misidentified it as either Cycas or Dioon edule. It was not until Standley and Williams’s 1949 visit to Dr. Isidoro Mejía in the city of Danlí that the species was recognised as distinct.
The specific epithet mejiae honours Dr. Isidoro Mejía, the Honduran physician and naturalist who provided the first detailed accounts of the wild tiusinte populations to Standley and Williams. Mejía had explored the species’ native range in northwestern Olancho circa 1910 — his field observations remained the only published source on wild Dioon mejiae for over 90 years until Bonta’s fieldwork in 2003.
POWO lists no synonyms. The native range is given as Honduras. Some sources (Stevenson et al. 2003; Bonta et al. 2006) mention the possibility of populations in northern Nicaragua, but this has not been confirmed. Dioon mejiae belongs to the “massive” clade of the genus alongside Dioon spinulosum and Dioon rzedowskii, sharing the group characters of large fronds, well-developed trunks, massive cones, and broad leaflets. It is considered closest to Dioon spinulosum on morphological grounds, but is immediately distinguished by a key vegetative character: its petiole bears spines/leaves along its entire length, while Dioon spinulosum has a smooth, leafless petiole.
The genus name Dioon derives from the Greek di- (two) and ōon (egg), referring to paired ovules. A common misconception equates the Honduran common name “teosinte” with the wild grass Zea mays subsp. parviglumis (the ancestor of maize) — but in Honduras, “teosinte/tiusinte” refers exclusively to this cycad, and the etymological connection to Nahuatl teocentli (“divine maize”) may reflect the deep historical integration of cycad seeds into Mesoamerican food systems alongside real maize.
Common names: Tiusinte, Teosinte, Teocinte, Palma Teosinte (Spanish/Honduras); Tiñuc (Tol/Jicaque language).
Morphological Description
Dioon mejiae is among the largest and most impressive cycads in the New World. The trunk is cylindrical, erect or sometimes leaning, reaching 7 m or more in height (some reports cite up to 7.3 m / 24 feet) and 17–36 cm in diameter. The trunk is clothed in persistent leaf bases and is extremely fire-resistant — mature plants survive the frequent burning of their habitat, thanks to the thick armour of old leaf bases and dense woolly hairs.
Leaves: numerous, forming a large, spreading crown. Individual fronds emerge from the trunk centre and are 1–2 m long. The leaves are flat, coriaceous, ascending to spreading. Leaflets are broad (comparable to Dioon spinulosum and Dioon rzedowskii), elongate-lanceolate, with smooth (entire) margins on mature plants — lacking the persistent spinules of Dioon spinulosum. Juvenile plants may have marginally toothed leaflets. A key diagnostic character is the petiole: in Dioon mejiae, the petiole and lower rachis bear spines and reduced leaflets along their entire length — a character that immediately separates this species from Dioon spinulosum (smooth petiole) and Dioon rzedowskii (smooth petiole). New leaves are tomentose (woolly); this tomentum can persist for some time, giving the annual flush of new leaves (locally called vestimento) a distinctive silvery appearance.
Cones: massive — among the largest in the genus. Female (seed) cones are ovoid, acuminate, greenish grey to pale brown, over 30 cm long, and can weigh up to 23 kg (50 lbs). Each cone can contain several hundred seeds. Male (pollen) cones are spindle-shaped, pale brown. The local Honduran lexicon includes specific terms for the cones: cabeza (female cone), churute (male cone). Coning frequency varies; in good years, a population of even a few hundred plants can produce dozens of harvestable cones.
Seeds: large, ovoid, with a fleshy sarcotesta. The seeds are the basis of the tiusinte food culture: they are rich in carbohydrates (predominantly starch, with an amylopectin:amylose ratio of approximately 2:1), proteins comparable to cereals, and contain over 50% resistant starch. However, they also contain cycasin and require detoxification processing before consumption — a procedure that local communities have practiced for centuries.
Similar Species and Common Confusions
| Character | Dioon mejiae | Dioon spinulosum | Dioon rzedowskii |
|---|---|---|---|
| Petiole | Spines/leaves along entire length | Smooth, leafless | Smooth, leafless |
| Leaflet margins (mature) | Entire (smooth) | Persistently spinulose | Entire (smooth) |
| Leaflet apex | Symmetrically tapering | Symmetrically tapering | Unequally tapering, deflected at tips |
| Adult trunk height | 7+ m | Up to 16 m | 5+ m |
| Habitat | Honduras, tropical semi-deciduous forest | Lowland Veracruz/Oaxaca, evergreen rainforest | Río Santo Domingo, semi-deciduous forest |
| Food use | Major dietary staple (~33,000 people) | Minor historical use | No significant food use documented |
| Distribution | Honduras (possibly Nicaragua) | Veracruz/Oaxaca, Mexico | Northern Oaxaca, Mexico |
The three massive-clade species can be reliably separated by the petiole character alone: armed in Dioon mejiae, smooth in the other two.
From Dioon spinulosum, the additional distinction is leaflet margins (entire in Dioon mejiae, spinulose in Dioon spinulosum).
From Dioon rzedowskii, the leaflet tip shape provides a further character (symmetrical in Dioon mejiae, asymmetric and deflected in Dioon rzedowskii).
Distribution and Natural Habitat
Dioon mejiae is endemic to northeastern Honduras, occurring in the departments of Olancho (the primary stronghold), Colón, and Yoro. The species’ native range covers approximately 5,000 km² — making it one of the more widely distributed Dioon species by area of occupancy. Wild populations are concentrated in the foothills and intermontane valleys of the Cordillera Nombre de Dios and the interior mountains of Olancho. Named population centres include Saguay, Río de Oro (Gualaco municipality), Jano, Manto, Sava, and Olanchito.
The habitat is tropical semi-deciduous forest, on steep slopes, in canyons, and also on relatively flat terrain. Some populations thrive on sandy or sandy-to-clayey alluvial deposits, while others grow in loamy, limestone-derived soils or in decomposed granite rich in humus. Dioon mejiae is typically an understory component of the forest but can persist in open pastures where the surrounding forest has been cleared — the fire-resistant trunks and deep roots allow adult plants to survive repeated burning and land clearing.
The Saguay tiusintal in Gualaco, Olancho, was historically one of the largest cycad populations documented anywhere in the world — containing over 300,000 adult plants and producing an estimated 15,000 harvestable female cones annually. This population has been reduced by almost half since the 1990s due to forest clearing for cattle pasture. The Río de Oro tiusintal contained approximately 20,000 plants and produced up to 1,000 cones per year.
Climate in the native range:
| Parameter | Estimated range (northeastern Honduras, 200–1,000 m) |
|---|---|
| Mean annual temperature | 22–26 °C |
| Average winter minimum | 16–20 °C |
| Estimated historical minimum | 8–12 °C (frost essentially absent) |
| Summer maximum average | 30–35 °C |
| Annual rainfall | 1,500–2,500 mm (summer-dominant, with some winter moisture from Caribbean systems) |
The climate is tropical, warm year-round, with no frost. This makes Dioon mejiae the least cold-hardy species in the genus — a direct consequence of its geographic isolation in the Central American tropics, well south of the frost-affected mountain habitats of the Mexican species.
Conservation
Dioon mejiae is classified as Vulnerable (VU) on the IUCN Red List. Despite the historically massive population sizes, the species is under severe and accelerating threat from three main factors: (1) timber extraction (logging of the surrounding forest exposes the cycads to desiccation and eliminates the forest canopy on which the understory plants depend); (2) cattle ranching (forest is cleared for pasture; although adult tiusintas survive the clearing, their regeneration is prevented); and (3) swidden agriculture (slash-and-burn clearing destroys juvenile plants and prevents recruitment). The Saguay tiusintal — once 300,000+ plants — has been halved since the 1990s.
However, Dioon mejiae benefits from a factor absent for most other Dioon species: traditional community protection. The tiusinte is a common-property resource, and traditional harvest regulation systems (the embargo system) still function in some communities. The mayor of Gualaco historically regulated the opening of the harvest season each year, based on the hunger level of the population and the state of the tiusintal. These traditional schemes represent a potential foundation for a more comprehensive conservation policy.
All Dioon species are listed on CITES Appendix II.
For buyers: Dioon mejiae is rare in international cultivation. Seeds and plants appear very sporadically from specialist dealers. Given the species’ critical conservation context, purchasing nursery-propagated plants is essential.
Cultivation
| Hardiness | ~0 to −2 °C (32 to 28 °F) / USDA zones 10a–11 |
| Light | Partial shade to full sun (naturally an understory species; tolerates full sun in humid climates) |
| Soil | Well-drained, humus-rich; tolerates a range of substrates |
| Watering | Moderate to regular — appreciates consistent moisture; more than dry-habitat Dioon |
| Adult size | Trunk to 7+ m (in centuries) × crown 2–3 m |
| Growth rate | Moderate |
| Difficulty | 3/5 |
Very limited published cultivation experience exists for Dioon mejiae outside of Honduras and a few botanical gardens. Geoff Stein (Dave’s Garden) describes it as “one of the three wide-leaf species” alongside Dioon spinulosum and Dioon rzedowskii, noting that its “petiole bears spines/leaves along the entire leaf length” — the key identification feature in cultivation. He notes that new leaves are “strikingly tomentose” and that the species is “adaptable” to both sun and partial shade.
Light: in the wild, Dioon mejiae is an understory species and naturally tolerates partial shade. However, it also persists in full sun in open pastures where the forest has been cleared. In cultivation, partial shade to full sun is appropriate, with partial shade preferred in hot, dry climates. In humid tropical climates, full sun is well tolerated.
Soil and drainage: the species grows on a wide range of substrates in habitat — sandy, alluvial, loamy, limestone-derived, and humus-rich decomposed granite. This suggests reasonable adaptability in cultivation. Well-drained but moisture-retentive soil is ideal — richer than the purely mineral mixes required for desert species like Dioon caputoi.
Watering: Dioon mejiae comes from a high-rainfall tropical habitat (1,500–2,500 mm). It appreciates regular moisture during the growing season — more than most other Dioon species. However, the general principle “less water is better” still applies relative to many tropical plants, and waterlogging remains harmful. In humid climates, natural rainfall may be sufficient.
Cold hardiness: this is the principal limitation for cultivation outside the tropics. Dioon mejiae is essentially a frost-free species from tropical Honduras where winter minimums rarely fall below 12 °C. Estimated cold tolerance is approximately 0 to −2 °C for very brief exposures — making it the least cold-hardy species in the genus. USDA zone 10a and above for year-round outdoor cultivation. In any zone with frost risk, container culture with warm overwintering is essential. Do not attempt outdoor cultivation in zones below 10a.
Container culture: the recommended approach for most growers outside the tropics. Use a well-drained but humus-rich mix. Overwinter in a warm location (minimum 10–12 °C). The species’ ultimate large size means that very large containers are needed for mature specimens.
Fertilization: responds well to regular feeding during the growing season, consistent with its high-rainfall tropical habitat.
Buying Advice
Availability: Dioon mejiae is very rare in the international cycad trade. Seeds are extremely difficult to obtain outside of Honduras. Specialist nurseries (Cycad International in Australia, occasional European dealers) may offer plants sporadically, but supply is unpredictable. This is a species that most collectors will encounter only in botanical gardens.
Identification: the armed petiole (spines and reduced leaflets along the entire length) is diagnostic and visible even on seedlings. This character alone separates Dioon mejiae from all other commonly cultivated Dioon species.
Propagation
Seed: the primary method. Seeds are large and germinate under standard conditions for the genus: remove sarcotesta (gloves essential — cycad seeds are toxic), soak 24–48 hours, sow horizontally in a well-draining but moisture-retentive mix, maintain 25–30 °C, keep medium consistently moist. Germination is cryptocotylar. In Honduras, natural germination occurs abundantly in forest understory — the species regenerates well when not suppressed by land clearing and cattle trampling.
Offsets: no specific information is available on offsetting frequency in cultivation.
Pests and Diseases
Root rot: the primary cultivation risk in cool, wet conditions. Ensure good drainage despite the species’ preference for moisture.
Cycad aulacaspis scale (Aulacaspis yasumatsui): likely susceptible, as are all Dioon species.
Eumaeus butterfly larvae: Eumaeus spp. (cycad butterflies) are known to feed on Dioon species throughout their range.
Landscape Use
Dioon mejiae is a spectacular landscape cycad for tropical and warm subtropical gardens. Its large stature, broad leaflets, and massive cones make it a commanding focal specimen — comparable to Dioon spinulosum in scale and visual impact. It is best suited to tropical climates (USDA zones 10–11) where frost is not a concern: southern Florida, Hawaii, northern Australia, and comparable regions. For non-tropical gardeners, it is primarily a botanical garden or conservatory specimen. Its cultural significance as the “tiusinte” of Honduras adds an extraordinary ethnobotanical dimension to any collection that includes it.
Frequently Asked Questions
Is Dioon mejiae really used as food?
Yes — and on a remarkable scale. An estimated 33,000 Hondurans use tiusinte seeds as a seasonal food. Female cones are harvested, seeds are detoxified through traditional processing (washing, soaking, grinding), and the resulting flour is made into tamales, tortillas, and other products. This is one of the few cycads on Earth that still functions as a genuine dietary staple for a large population.
Is Dioon mejiae the only Dioon outside Mexico?
Yes. All other 17 accepted species of Dioon are Mexican endemics. Dioon mejiae is the sole Central American representative of the genus, restricted to Honduras (with unconfirmed reports from northern Nicaragua). Its geographic isolation from the Mexican species is a consequence of the genus’s ancient history and the relatively recent (Pliocene) formation of the Isthmus of Panama — the large, heavy seeds of Dioon are thought to have been a barrier to further southward dispersal.
How cold-hardy is Dioon mejiae?
It is the least cold-hardy species in the genus. As a tropical species from frost-free Honduras, it tolerates only very brief exposures to approximately 0 to −2 °C. USDA zone 10a minimum for outdoor cultivation. Not suitable for any climate with regular frost.
How does Dioon mejiae differ from Dioon spinulosum?
Two key characters: (1) the petiole is armed with spines/reduced leaflets along its entire length in Dioon mejiae (smooth in Dioon spinulosum); (2) mature leaflet margins are entire (smooth) in Dioon mejiae (persistently spinulose in Dioon spinulosum). Geographically, Dioon mejiae is Honduran while Dioon spinulosum is Mexican.
Is Dioon mejiae toxic?
Yes. Like all cycads, it contains cycasin and other toxic compounds. The seeds, leaves, and roots are poisonous to mammals. The Honduran food use requires extensive traditional detoxification processing — the seeds are never consumed raw. Modern nutritional analyses (Bastías et al.) confirm high resistant starch content and adequate protein but also the presence of toxic compounds requiring careful processing.
Authority Websites and Databases
POWO — Plants of the World Online (Kew)
https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:80653-2
The accepted nomenclatural record: native range Honduras. No synonyms listed.
World List of Cycads — cycadlist.org
https://cycadlist.org/scientific_name/253
Nomenclatural record: type data, etymology, distribution, IUCN status, and common names including “tiusinte” and “tiñuc” (Tol/Jicaque language).
IUCN Red List — Dioon mejiae
https://www.iucnredlist.org/species/42130/10661262
The Vulnerable (VU) assessment with population data, threat analysis, and habitat description.
Bonta, Flores Pinot, Graham, Haynes & Sandoval (2006) — Ethnobotany of tiusinte
https://bioone.org/journals/journal-of-ethnobiology/volume-26/issue-2/0278-0771_2006_26_228_EACOTD_2.0.CO_2/
The landmark ethnobotanical study in the Journal of Ethnobiology. Documents the 33,000-person food culture, traditional harvest regulation (the embargo system), the 60+ specialised terms in the tiusinte lexicon, and conservation threats. Essential reading — this paper transforms the understanding of Dioon mejiae from a botanical curiosity to a species of profound cultural and food-security importance.
Standley & Williams (1950) — original description
Standley, P. C., & Williams, L. O. (1950). Dioon mejiae, a new cycad from Honduras. Ceiba, 1, 36–38.
The protologue. Based on cultivated material from Francisco Morazán, El Paraíso, and Olancho departments.
FloraFinder — Dioon mejiae
https://florafinder.org/Species/Dioon_mejiae.php
Concise species profile: height to 7.3 m, leaf length 1–2 m, smooth leaf margins, habitat in semi-deciduous tropical forest.
iNaturalist
https://www.inaturalist.org/taxa/136082-Dioon-mejiae
Citizen science observations from Honduras.
Dave’s Garden — Dioons: The Hardy Mexican Cycads
https://davesgarden.com/guides/articles/view/1981/
Grower’s guide by Geoff Stein. Notes Dioon mejiae as one of the three “wide-leaf” species, with spines/leaves along the entire petiole length — the key separation from Dioon spinulosum.
IUCN/SSC Cycad Specialist Group — Cycadales
https://www.cycadascolombia.org/eng/cycadales.html
Overview of all cycad genera and species diversity. Notes 18 species in Dioon, with Dioon mejiae as the sole extra-Mexican species.
Bonta & Osborne — Cycads in the Vernacular
http://www.cycad.org/documents/Bonta-Osborne-Cycads-Vernacular.pdf
A comprehensive compendium of local names for cycads worldwide. Documents over 60 specialised terms in the Honduran tiusinte lexicon, including churute (pollen cone), cabeza (female cone), vestimento (leaf flush), pan de tiusinte (cycad bread), and embargo (closed harvest season).
Bibliography
Bonta, M., Flores Pinot, O., Graham, D., Haynes, J., & Sandoval, G. (2006). Ethnobotany and conservation of tiusinte (Dioon mejiae Standl. & L.O. Williams, Zamiaceae) in northeastern Honduras. Journal of Ethnobiology, 26(2), 228–257.
De Luca, P., & Sabato, S. (1978). Dioon mejiae. Enciclopedia Agraria Italiana, 3rd suppl.
Haynes, J. L. (2022). Etymological compendium of cycad names. Phytotaxa, 550(1), 1–31.
Jones, D. L. (1993). Cycads of the World. Reed, Chatswood, NSW.
Moretti, A., Caputo, P., Cozzolino, S., De Luca, P., Gaudio, L., Gigliano Siniscalco, G., & Stevenson, D. W. (1993). A phylogenetic analysis of Dioon (Zamiaceae). American Journal of Botany, 80, 204–214.
Norstog, K. J., & Nicholls, T. J. (1997). The Biology of the Cycads. Cornell University Press, Ithaca.
Standley, P. C., & Williams, L. O. (1950). Dioon mejiae, a new cycad from Honduras. Ceiba, 1, 36–38.
Stevenson, D. W., Vovides, A., & Chemnick, J. (2003). Regional overview: New World. In: Donaldson, J. S. (ed.), Cycads: Status Survey and Conservation Action Plan, 31–38. IUCN, Gland.
Whitelock, L. M. (2002). The Cycads. Timber Press, Portland.