The final chapter in the dismemberment of Dioon merolae was written in December 2021, when Gutiérrez-Ortega, Pérez-Farrera, Chemnick, and Gregory described Dioon salas-moralesiae from southeastern Oaxaca — the populations on the western side of the Isthmus of Tehuantepec that had long been lumped with true Dioon merolae from Chiapas. With this description, the old Dioon merolae concept — once broadly applied to all “venetian blind” Dioon populations from central Oaxaca to Chiapas — was resolved into three species: Dioon oaxacensis (central valleys of Oaxaca, 2020), Dioon salas-moralesiae (southeastern Oaxaca, 2021), and Dioon merolae sensu stricto (Chiapas, retained). The Isthmus of Tehuantepec — the narrowest point of the Mexican landmass, a lowland corridor barely 200 km wide between the Pacific and the Gulf — serves as the biogeographic divide: Dioon salas-moralesiae on the western side, Dioon merolae on the eastern side.
The species is named for Dr. Silvia Hortensia Salas-Morales, co-founder of SERBO (Sociedad para el Estudio de los Recursos Bióticos de Oaxaca) — the same remarkable woman whose field explorations across Oaxaca’s mountains and canyons led to the discovery of Dioon argenteum (2003), Dioon planifolium (2016), and the populations that became Dioon oaxacensis. In naming this species for her, the authors honoured the person who has arguably done more than anyone to reveal the hidden Dioon diversity of Oaxaca.
Quick Facts
| Scientific name | Dioon salas-moralesiae Gut.Ortega & Pérez-Farr. |
| Family | Zamiaceae |
| Origin | Southern Mexico — southeastern Oaxaca (western side of the Isthmus of Tehuantepec) |
| Adult size | Medium; similar stature to Dioon merolae |
| Hardiness | −1 to −3 °C (30 to 27 °F) / USDA zones 10a–11 (estimated) |
| IUCN | Not yet formally assessed (considered “threatened with extinction” under NOM-059) |
| CITES | Appendix II (all Dioon species) |
| Cultivation difficulty | 3/5 (estimated) |
Taxonomy and Nomenclature
Dioon salas-moralesiae was described by José Said Gutiérrez-Ortega and Miguel Ángel Pérez-Farrera, with Jeffrey Chemnick and Timothy J. Gregory, in 2021, in Phytotaxa 528(2): 93–110, figs. 10–13. The holotype was collected by Pérez-Farrera and Gutiérrez-Ortega (no. 3466, female plant) in southeastern Oaxaca.
A note on spelling: the protologue published the epithet as “salas-moralesae,” but under ICN Art. 60.12 the correct form for a feminine personal name ending in a consonant is -iae, yielding salas-moralesiae. Both spellings appear in the literature; cycadlist.org and WFO use the corrected form.
The specific epithet honours Dr. Silvia Hortensia Salas-Morales, co-founder and driving force of SERBO — the Oaxacan conservation organisation that has systematically mapped and surveyed the forests of Oaxaca for over three decades. Salas-Morales is responsible for the discovery of numerous cycad populations across the state, including the type populations of Dioon argenteum, Dioon planifolium, and the populations that became Dioon oaxacensis. The naming of a species in her honour recognises a career of extraordinary field dedication in one of the most biodiverse and taxonomically challenging regions on Earth.
The triple split of Dioon merolae — completed:
The description of Dioon salas-moralesiae completes the resolution of the old Dioon merolae concept into three species. The sequence of discoveries proceeded through two complementary studies:
- Gutiérrez-Ortega et al. (2020, New Phytologist): a niche conservatism study demonstrated that the Dioon merolae populations from Oaxaca and Chiapas represent three genetically distinct lineages: “West-A” (central valleys of Oaxaca), “West-B” (southeastern Oaxaca, western side of the Isthmus), and “East” (Chiapas, eastern side of the Isthmus).
- Gutiérrez-Ortega et al. (2020, Phytotaxa): “West-A” was described as Dioon oaxacensis.
- Gutiérrez-Ortega et al. (2021, Phytotaxa): the remaining “West-B” populations — those on the western side of the Isthmus — were found to differ conspicuously from “East” (true Dioon merolae) in morphological and morphometric characters, and were described as Dioon salas-moralesiae.
The Isthmus of Tehuantepec thus emerges as the key biogeographic barrier separating Dioon salas-moralesiae (western side) from Dioon merolae sensu stricto (eastern side). This is consistent with the Isthmus’s well-documented role as a biogeographic divide for many plant and animal groups across Mesoamerica.
Phylogenetic position: within the “merolae” lineage of the Purpusii clade. Dioon salas-moralesiae shows intermediate morphological characteristics between Dioon oaxacensis and Dioon merolae: qualitatively it resembles Dioon merolae, but morphometrically it is closer to Dioon oaxacensis in several characters (except trunk diameter, petiole length, and mid-leaflet width). This intermediate position suggests a gradational divergence along the Oaxaca–Chiapas axis.
POWO lists no synonyms.
Common names: no established common name.
Morphological Description
Dioon salas-moralesiae is morphologically intermediate between Dioon oaxacensis (from the arid central valleys) and Dioon merolae (from Chiapas). The protologue provides detailed morphometric comparisons using statistical tests, but much of the data is behind a paywall. Key published characters include:
Trunk: cylindrical, erect. Medium-sized for the genus.
Leaves: forming a crown similar in general architecture to Dioon merolae. The leaves have the characteristic imbricate leaflet arrangement (“venetian blind” effect) shared with the entire merolae complex.
Leaflets: the diagnostic differences from Dioon merolae are subtle but consistent and confirmed by morphometric analysis. The leaflets show qualitative similarities to Dioon merolae (e.g., the slightly deflected posture, the imbricate arrangement) but morphometric similarity to Dioon oaxacensis in several dimensional characters. The leaflet apex curvature is a key discriminating character: in the identification key (Gutiérrez-Ortega et al. 2020), Dioon merolae is separated from the other members of the complex by “leaflets curved at the apical section.”
Reproductive structures: dioecious. Female megasporophylls and male cones consistent with the merolae complex but differing in dimensional details.
Seeds: ovoid, with cream/white sarcotesta.
Similar Species and Common Confusions
| Character | Dioon salas-moralesiae | Dioon merolae | Dioon oaxacensis |
|---|---|---|---|
| Leaflet posture | Slightly deflected (intermediate) | Slightly deflected (“venetian blind”) | Flat, stiff, straight |
| Leaflet imbrication | Imbricate (intermediate) | Strongly imbricate | Slightly imbricate |
| Rachis colour (mature) | Intermediate | Greener | Yellowish |
| Reproductive structures | Intermediate | Smaller | Larger |
| Morphometric affinity | Closer to D. oaxacensis | Distinct | Closer to D. salas-moralesiae |
| Qualitative affinity | Closer to D. merolae | Closest | Distinct |
| Distribution | SE Oaxaca (W of Isthmus) | Chiapas (E of Isthmus) | Central valleys of Oaxaca |
The identification challenge is real: Dioon salas-moralesiae is morphologically intermediate between its two relatives, with qualitative characters resembling Dioon merolae and dimensional characters resembling Dioon oaxacensis. In practice, geography is the most reliable identifier: populations in southeastern Oaxaca, on the western side of the Isthmus of Tehuantepec = Dioon salas-moralesiae; populations in Chiapas, on the eastern side = Dioon merolae; populations in the arid central valleys = Dioon oaxacensis.
Distribution and Natural Habitat
Dioon salas-moralesiae is endemic to southeastern Oaxaca, on the western side of the Isthmus of Tehuantepec. The populations occur in the districts and municipalities of this region, in habitat similar to that of Dioon merolae: tropical deciduous forest and transitional vegetation on rocky slopes.
The Isthmus of Tehuantepec is the critical geographic feature. At only ~200 km wide and with a maximum elevation of barely 250 m, the Isthmus is the lowest point between the Pacific and the Gulf in all of Mexico. It has long been recognised as a major biogeographic barrier — or corridor, depending on the organism — separating Oaxacan and Chiapan biotas. For Dioon, the Isthmus appears to have acted as a barrier to gene flow between the southeastern Oaxacan populations (D. salas-moralesiae) and the Chiapan populations (D. merolae), allowing morphological and genetic divergence to accumulate.
The habitat is characterised by seasonal tropical deciduous forest with a pronounced dry season. Rocky hillsides with well-drained substrates are typical. The vegetation includes the expected Mesoamerican dry-forest elements: Bursera, leguminous trees, cacti, and associated xerophytes.
Climate in the native range:
| Parameter | Estimated range (SE Oaxaca, W of Isthmus) |
|---|---|
| Mean annual temperature | 22–28 °C |
| Mean January minimum | 12–18 °C |
| Historical minimum | 5–10 °C (frost very rare at low elevations) |
| Mean summer maximum | 32–36 °C |
| Annual rainfall | 600–1,000 mm (summer-dominant) |
| Dry season | November–May |
The climate is warmer and more tropical than the central valleys (where Dioon oaxacensis occurs) but drier than the Chiapan slopes where Dioon merolae sensu stricto grows. This intermediate climate mirrors the species’ intermediate morphology.
Conservation
Dioon salas-moralesiae has not yet received a formal IUCN assessment. However, the protologue explicitly states that, as a subdivision of the former Dioon merolae concept, it should be considered “threatened with extinction” (category “P”) under the Mexican Official Norm NOM-059-SEMARNAT-2010. The previous Dioon merolae (sensu lato) was listed as Vulnerable (VU). With the narrower circumscription resulting from the triple split, each daughter species has a smaller range and population than the original concept, making all three potentially more threatened than the parent taxon.
The main threats are consistent with those affecting all Oaxacan Dioon species: habitat destruction (agriculture, cattle ranching, road construction), fire, and overcollection for the horticultural trade. The proximity of the Isthmus of Tehuantepec — one of the most developed and infrastructure-heavy corridors in southern Mexico, including wind farms, highways, and the proposed Interoceanic Corridor — adds a layer of anthropogenic threat not shared by the more remote canyon species.
All Dioon species are listed on CITES Appendix II.
Cultivation
| Hardiness | −1 to −3 °C (30 to 27 °F) / USDA zones 10a–11 (estimated) |
| Light | Full sun to partial shade |
| Soil | Well-drained, mineral-dominant |
| Watering | Moderate in summer, reduced in winter; less water is better |
| Adult size | Medium |
| Growth rate | Slow |
| Difficulty | 3/5 (estimated) |
No published cultivation data exists for Dioon salas-moralesiae. The species was only described in 2021 and is essentially unknown in cultivation. Recommendations are extrapolated from the ecology of the native habitat and from the cultivation of Dioon merolae, which has been in specialist collections for decades.
Light: full sun to partial shade. The tropical deciduous forest habitat suggests tolerance of both conditions, with good light levels preferred for optimal growth.
Soil and drainage: well-drained, mineral-dominant substrate. Rocky hillside habitat with rapid drainage is the natural condition.
Watering: less water is better. Seasonal watering matching the summer monsoon pattern: moderate during the warm growing season, reduced to minimal in the dry winter months.
Cold hardiness: limited. The low-elevation, near-tropical southeastern Oaxacan habitat suggests less frost tolerance than the highland species. Estimated −1 to −3 °C. USDA zone 10a minimum. The warmer climate of the Isthmus region means this species is less cold-hardy than Dioon oaxacensis or the Oaxacan canyon species.
Container culture: the practical option for all growers outside the tropics. Well-draining mineral mix, warm bright position, seasonal watering.
Fertilization: light applications of slow-release fertilizer during the growing season.
Buying Advice
Availability: Dioon salas-moralesiae is unavailable in the international trade. Described only in December 2021, no legal propagation programme exists. Plants previously in circulation as “Dioon merolae” from southeastern Oaxaca may in fact be Dioon salas-moralesiae, but without provenance documentation, identification is difficult.
Propagation
Seed: standard Dioon protocol. Remove sarcotesta, soak 24–48 hours, sow horizontally in a well-draining mineral mix at 25–30 °C. Germination is cryptocotylar.
Offsets: no specific data.
Pests and Diseases
Root rot: the primary cultivation risk. Prevention through substrate choice and seasonal watering discipline.
Cycad aulacaspis scale (Aulacaspis yasumatsui): susceptibility presumed similar to Dioon merolae.
Landscape Use
Dioon salas-moralesiae is, for now, a species of primarily scientific interest rather than horticultural availability. Its intermediate morphology between Dioon oaxacensis and Dioon merolae makes it a fascinating subject for understanding speciation across the Isthmus of Tehuantepec — one of the most important biogeographic boundaries in the Americas. If ever propagated, its warm-climate requirements, medium stature, and imbricate leaflet arrangement would make it an attractive specimen for tropical and subtropical gardens, alongside other Mesoamerican dry-forest plants. For the collector assembling a complete Dioon collection, this species represents the final piece of the genus — species number 18 of 18.
Frequently Asked Questions
What is Dioon salas-moralesiae?
It is the most recently described species in the genus Dioon, published in December 2021. It was carved from the old Dioon merolae concept — the third and final species to emerge from that taxonomic reassessment (after Dioon oaxacensis in 2020). It is endemic to southeastern Oaxaca, on the western side of the Isthmus of Tehuantepec.
Who is Silvia Salas-Morales?
Dr. Silvia Hortensia Salas-Morales is the co-founder of SERBO (Sociedad para el Estudio de los Recursos Bióticos de Oaxaca), the Oaxacan conservation organisation whose systematic botanical explorations over three decades have revealed extraordinary plant diversity across the state. She is responsible for the discovery of the populations that became Dioon argenteum, Dioon planifolium, and Dioon oaxacensis, and is a co-author on several Dioon species descriptions. The naming of Dioon salas-moralesiae in her honour recognises her unrivalled contribution to Oaxacan cycad discovery.
How does the Isthmus of Tehuantepec divide Dioon species?
The Isthmus — barely 200 km wide and only 250 m at its highest point — is a major biogeographic barrier in Mesoamerica. For Dioon, it separates Dioon salas-moralesiae (western side, southeastern Oaxaca) from Dioon merolae sensu stricto (eastern side, Chiapas). The lowland corridor of the Isthmus likely interrupted gene flow between the two populations, allowing them to diverge into distinct species.
How do you distinguish Dioon salas-moralesiae from Dioon merolae?
With difficulty, based on gross morphology alone. The species is morphologically intermediate between Dioon oaxacensis and Dioon merolae, with qualitative characters resembling Dioon merolae but dimensional characters closer to Dioon oaxacensis. In practice, geography is the most reliable identifier: southeastern Oaxaca (western side of the Isthmus) = Dioon salas-moralesiae; Chiapas (eastern side) = Dioon merolae.
Is Dioon salas-moralesiae toxic?
Yes. Like all cycads, all parts contain cycasin and other toxic glycosides. Seeds, leaves, and roots are poisonous to dogs, cats, livestock, and humans.
Authority Websites and Databases
POWO — Plants of the World Online (Kew)
https://powo.science.kew.org/taxon/…
The accepted nomenclatural record (under corrected spelling salas-moralesiae). Native range: Mexico (Oaxaca). Seasonally dry tropical biome.
World List of Cycads — cycadlist.org
https://cycadlist.org/scientific_name/895
Nomenclatural record: first published in Phytotaxa 528(2): 93–110 (2021). Etymology (Haynes 2022): honouring Dr. Silvia Hortensia Salas-Morales, co-founder of SERBO, for her contributions to the knowledge of Oaxacan flora and the discovery of numerous cycad populations. Type: Pérez-Farrera & Gutiérrez-Ortega 3466 (female).
Gutiérrez-Ortega et al. (2021) — protologue
https://doi.org/10.11646/phytotaxa.528.2.3
The original species description in Phytotaxa 528(2): 93–110. Full morphological description and morphometric comparisons among all three species of the former Dioon merolae complex. Includes statistical tests confirming that the southeastern Oaxacan populations differ significantly from Chiapan Dioon merolae. Discusses the Isthmus of Tehuantepec as the biogeographic barrier and the implications for species delimitation criteria across the genus.
Gutiérrez-Ortega et al. (2020) — Niche conservatism in Dioon merolae
https://doi.org/10.1111/nph.16647
The New Phytologist study that first revealed the three-lineage structure within Dioon merolae. Demonstrates that niche conservatism — the tendency of species to retain their ancestral ecological preferences — promotes speciation in cycads by maintaining populations in similar but geographically isolated habitats.
Gutiérrez-Ortega et al. (2020) — Dioon oaxacensis description
https://doi.org/10.11646/phytotaxa.474.1.5
The companion paper describing the first species split from Dioon merolae. Includes the identification key that separates all Oaxacan Dioon species and the comparative table between D. oaxacensis and D. merolae that provides context for understanding D. salas-moralesiae.
Dorsey et al. (2018) — Pleistocene diversification in Dioon
https://doi.org/10.1002/ajb2.1149
Genus-wide molecular phylogeny providing the broader context for the “merolae” lineage within the Purpusii clade.
Bibliography
Chemnick, J., Gregory, T. J., & Salas-Morales, S. (1997). A revision of Dioon tomasellii (Zamiaceae) from western Mexico, a range extension of D. merolae, and clarification of D. purpusii. Phytologia, 83(1), 1–6.
Dorsey, B. L., Gregory, T. J., Sass, C., & Specht, C. D. (2018). Pleistocene diversification in an ancient lineage: a role for glacial cycles in the evolutionary history of Dioon Lindl. (Zamiaceae). American Journal of Botany, 105(9), 1512–1530.
Gutiérrez-Ortega, J. S., Pérez-Farrera, M. A., Vovides, A. P., Salas-Morales, S. H., & Chemnick, J. (2020). Dioon oaxacensis (Zamiaceae): a new cycad species from the arid central valleys of Oaxaca (Mexico). Phytotaxa, 474(1), 51–61.
Gutiérrez-Ortega, J. S., Salinas-Rodríguez, M. M., Ito, T., et al. (2020). Niche conservatism promotes speciation in cycads: the case of Dioon merolae (Zamiaceae) in Mexico. New Phytologist, 227(6), 1872–1884.
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.
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.
Norstog, K. J., & Nicholls, T. J. (1997). The Biology of the Cycads. Cornell University Press, Ithaca.
Whitelock, L. M. (2002). The Cycads. Timber Press, Portland.