Dioon planifolium

Dioon planifolium is a cycad endemic to the Mixteca region of north-western Oaxaca, Mexico, where it grows on steep hillsides at around 1,400 to 1,650 m, in a dry habitat rich in cacti and other succulents. Described in 2016, this species of the genus Dioon was the first cycad ever recorded in the Mixteca. Its name refers to its flat leaves, whose narrow leaflets have entire margins or carry only one or two spines. Listed as Vulnerable on the IUCN Red List, it is almost unknown in cultivation outside a handful of botanic gardens.

Key facts about Dioon planifolium

  • Accepted name: Dioon planifolium Salas-Mor., Chemnick & T.J.Greg. (2016), 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: none
  • Family: Zamiaceae, order Cycadales
  • Common names: no English name attested; the Spanish “palma real” and “cícada” given by CONABIO are generic names for Mexican cycads
  • Natural range: Mexico, north-western Oaxaca (Mixteca, valley of the Río Mixteco, municipality of San Jorge Nuchita)
  • IUCN status: Vulnerable (VU C1; D2), assessment by Gregory and Chemnick published in 2022
  • CITES and other protection: CITES Appendix II, through the listing of the whole family Zamiaceae (annotation #4); Annex B in the European Union; not listed in the Mexican standard NOM-059-SEMARNAT-2010, nor in its 2019 update
  • Documented hardiness: no data (see Cold hardiness)
  • Light and soil: in the wild, steep hillsides in xerophytic scrub, dry tropical forest and oak woodland; not documented in cultivation
  • Habit and adult size: plants 1 to 4 m tall, trunk 20 to 25 cm across; 25 to 40 leaves 90 to 220 cm long (2020 revision)
  • In the UK, US and Australia: Montgomery Botanical Center (three accessions, 2001 and 2004), Fairchild and five other American gardens (BGCI); no British or Australian garden listed
  • Toxicity: no data for the species; toxins documented in other cycads (see Toxicity and precautions)

How to recognise Dioon planifolium

Dioon planifolium is recognised by its flat leaves and its leaflets that do not overlap, with entire margins or at most one or two spines towards the tip. The original description, in the Cactus and Succulent Journal, is only available by subscription; its abstract gives the habitat and the region. The detailed description below comes from the taxonomic revision of Hernández-Tapia and co-authors (2020), several points of which were disputed by Haynes (2020):

  • Habit: plants 1 to 4 m tall, with a trunk 20 to 25 cm in diameter; scale leaves (cataphylls) triangular, long-pointed and woolly;
  • Leaves: 25 to 40 in the crown, 90 to 220 cm long and 13 to 24 cm wide, becoming hairless, with whitish-brown hairs; petiole 8 to 19 cm, woolly at the base;
  • Leaflets: 91 to 144 pairs, linear-lanceolate, flat, not overlapping, opposite or nearly so; margins entire, sometimes with one or two spines near the tip; mid-leaf leaflets 6 to 9.5 cm long, all 4 to 6 mm wide; no leaflets reduced to spines at the base of the leaf;
  • Male cones: cylindrical, 30 to 39 cm long and 8 to 11.5 cm wide;
  • Female cones: ovoid, 38.7 to 51 cm long and 19 to 20.5 cm wide;
  • Seeds: ovoid to almost spherical, 3.3 to 4.3 cm long, with a yellow outer coat (sarcotesta).

The published identification keys do not fully agree. That of Gutiérrez-Ortega and co-authors (2021) places Dioon planifolium among the species with unkeeled leaves and non-overlapping leaflets more than 5 mm wide, closely spaced and flat, with none to two long spines on the upper margin. That of Martínez-Domínguez and co-authors (2026), on the contrary, puts it among the species with keeled leaves, and separates it from Dioon purpusii by the base of the petiole, hairless at maturity, and by the curved tip of the male cone scales. The leaflet width also differs between sources (4 to 6 mm, or more than 5 mm).

Hybrids

No hybrid of Dioon planifolium has been reported.

Possible confusion

According to the keys, the closest species is Dioon holmgrenii, from the Pacific slope of Oaxaca. The 2021 key separates the two by the flat leaflets of Dioon planifolium, with none to two long spines, against three or four spines and slightly curved leaflets in Dioon holmgrenii. The 2020 revision adds that Dioon planifolium has long-pointed trunk scales, flat leaves and leaflets with entire margins or a single spine.

Dioon caputoi, which also grows in a dry habitat in the region, has narrower leaflets (4 to 5 mm) widely spaced along the rachis. Dioon purpusii has keeled leaves, spiny leaflets and a woolly petiole base. Without documented provenance, a young Dioon with narrow leaflets cannot be assigned to this species with any confidence.

Taxonomy

Dioon planifolium is an accepted name without synonyms. Silvia H. Salas-Morales, Jeffrey Chemnick and Timothy J. Gregory described it in 2016 in the Cactus and Succulent Journal (88(1): 35–42, according to Crossref and the species page of The World List of Cycads). The holotype (Salas-Morales 4344) was collected on 3 November 2001 on the steep hillsides on the east side of the valley of the Río Mixteco, at about 1,600 m; it is kept at the National Herbarium of Mexico (MEXU), with isotypes at CAS, F, FTG, SERO and XAL. The 2020 revision places the locality in the municipality of San Jorge Nuchita.

Gutiérrez-Ortega and co-authors (2021) place Dioon planifolium in the “Purpusii clade”, together with Dioon purpusii, Dioon argenteum, Dioon califanoi, Dioon caputoi, Dioon holmgrenii, Dioon merolae, Dioon oaxacensis and Dioon salas-moralesiae. Its exact position within this group has not been published.

Etymology and history

The epithet planifolium combines the Latin planus, “flat”, and folium, “leaf”, in reference to the characteristically flat leaves (Haynes, 2022, as given by The World List of Cycads). According to the abstract of the description, it is the first cycad found in the Mixteca region of Mexico. The type was collected in 2001, fifteen years before the name was published, and the Montgomery Botanical Center catalogue lists two accessions from that same year and one from 2004: the species was therefore already in that collection well before it had a name. Its wider introduction into cultivation is not documented.

Common names

No English common name is attested. The Enciclovida database of CONABIO, the Mexican biodiversity agency, gives “palma real o cícada”, two generic Spanish names applied to several Mexican cycads. No local name specific to the species is documented, and “flat-leaved dioon”, seen online, is not confirmed by any reference source.

In the wild

Dioon planifolium is endemic to the Mixteca of north-western Oaxaca. According to the abstract of its description, it grows in a dry habitat rich in cacti and succulents. The 2020 revision records it in xerophytic scrub, dry tropical forest and oak woodland, between 1,400 and 1,650 m, under warm and humid, semi-arid or temperate climates; the same revision nevertheless lists collections at 1,249 m and 2,090 m, which casts some doubt on that range. The number of populations and their size are not published in the sources available.

Skelley and co-authors (2022) note that Dioon planifolium, whose range lies close to those of Dioon califanoi, Dioon caputoi and Dioon purpusii, may host the small cone beetle Pharaxonotha bicolor, but no sampling has been published. Its pollinators are not known.

Conservation status and regulation

Dioon planifolium is listed as Vulnerable (VU) on the IUCN Red List under criteria C1 and D2, in an assessment by Timothy Gregory and Jeffrey Chemnick dated 3 February 2020 and published in 2022 (The World List of Cycads, GBIF, Crossref). Criterion C1 refers to a small population, fewer than 10,000 mature individuals, in continuing decline; criterion D2 to a very restricted area of occupancy or a very small number of locations exposed to a plausible threat.

Species+ does not list the species by name, but the listing of the whole family Zamiaceae in CITES Appendix II (annotation #4) and in Annex B of the European regulation (Regulation (EU) 2026/1383, in force since 29 June 2026) applies to it; Enciclovida also records it in Appendix II. Described in 2016, it appears neither in the Mexican standard NOM-059-SEMARNAT-2010 nor in the 2019 update of its list. Any plant bought must come from cultivation and carry the required documents. Databases checked on 26 October 2026: check the regulations in force before any purchase.

Growing Dioon planifolium

No published source describes the cultivation of Dioon planifolium, and no commercial offer is documented. Its natural habitat, dry hillsides rich in succulents, points to a mineral, free-draining mix and moderate watering, but these are precautions deduced from the habitat, not tested advice. At Nong Nooch Tropical Botanical Garden, in Thailand, the cycad curator wrote in 2022 that all described Dioon are grown there and produce cones, without detail on this species.

Outdoor and in-ground cultivation

No outdoor planting is documented, whether in the Mediterranean, California, Florida or Australia, and no observation of the species has been published for the Jardin zoologique tropical at La Londe-les-Maures, in the Var. The American gardens that hold it have published nothing on its behaviour.

Container cultivation

In climates with frost, a pot with a gritty mineral mix, kept dry and frost-free in winter, is the prudent option until its tolerance has been documented.

In cultivation in the UK, US and Australia

  • United Kingdom: no British garden declares the species to BGCI PlantSearch.
  • United States: the Montgomery Botanical Center (Coral Gables, Florida) lists three accessions in its online catalogue, two from 2001 and one from 2004; the Fairchild Tropical Botanic Garden (Miami) listed it in its online catalogue in October 2026. BGCI PlantSearch also lists Ganna Walska Lotusland, the Huntington, Descanso Gardens, the San Diego Zoo and Naples Botanical Garden. A BGCI listing is a declaration by the garden, not proof that the plant is alive today.
  • Australia: no Australian garden declares the species to BGCI.

Propagation

No propagation data specific to the species have been published. As in other Dioon, there are separate male and female plants and seed is the usual route; nothing has been published on germination or on offsets in this species.

Pests and diseases

No disease or pest specific to Dioon planifolium is documented.

Cold hardiness

No data on the cold tolerance of Dioon planifolium have been published.

Mediterranean and European experience

No cultivation report is documented in France or elsewhere in Mediterranean Europe.

United Kingdom, United States and Australia

No hardiness value, measured or claimed by a nursery, has been published, and no dated report from a British, American or Australian grower has been found. The altitude of the localities, around 1,400 to 1,650 m, and the presence of oak woodland suggest cool winter nights, but no temperature record has been published for them.

Toxicity and precautions

No toxicity data have been published for Dioon planifolium. 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. No traditional use specific to the species has been documented.

Frequently asked questions

What does the name planifolium mean?

“Flat-leaved”, from the Latin planus and folium. It refers to the flat leaves of the species. A key published in 2026 nevertheless places it among the Dioon with keeled leaves, a sign that the character varies or is still debated.

How can Dioon planifolium be recognised?

By its almost spineless leaflets. They are flat, narrow and do not overlap, with at most one or two spines towards the tip, whereas those of Dioon holmgrenii and Dioon purpusii carry more. A documented provenance from the Mixteca of Oaxaca remains the surest clue.

Where does it grow?

In the Mixteca, in north-western Oaxaca. It grows on steep hillsides, in a dry habitat rich in cacti and succulents, at around 1,400 to 1,650 m. It was the first cycad recorded in that region.

Is it endangered?

Yes. The IUCN lists it as Vulnerable because of its small population and very restricted range. It is also protected by CITES, like all Zamiaceae.

Is it hardy?

Not known. No trial has been published and no commercial offer is documented. Grow it in a pot and keep it frost-free and dry in winter.

Is it toxic?

It should be treated as such. There are no data for the species, but other cycads contain toxins dangerous to people and animals.

Further reading on Succulentes

Sources

Reference sites

Bibliography

  • Salas-Morales, S.H., Chemnick, J. & Gregory, T.J. (2016). A new cycad species in the genus Dioon (Zamiaceae) from the Mixteca region of Oaxaca, Mexico. Cactus and Succulent Journal (Los Angeles) 88(1): 35–42. doi:10.2985/015.088.0104 [Protologue; 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 [Description, habitat, type locality; 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. [Possible host of Pharaxonotha bicolor; open-access article.]
  • Gregory, T. & Chemnick, J. (2022). Dioon planifolium. The IUCN Red List of Threatened Species 2022: e.T103632265A103632300. doi:10.2305/IUCN.UK.2022-1.RLTS.T103632265A103632300.en [Category VU C1; D2; 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 [Etymology, 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 planifolium.]
  • 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.]