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| Dioon nuusaviorum Mart.-Domínguez, Nic.-Mor. & D.W.Stev., in Martínez-Domínguez, Nicolalde-Morejón, Stevenson, Lorea-Hernández et Vergara-Silva, 2026. |
Abstract
Taxonomic studies in cycad genera using multiple approaches have refined the delimitation of many species. In the case of Dioon Lindl., a Mesoamerican genus, a reliable classification has been achieved through taxonomic work carried out since the description of the genus and pioneering studies in Mexico during the 1980–90s. Here, we describe a new species from Guerrero based on evidence collected from populations encountered during fieldwork carried out in 2019. These populations had previously been considered morphologically similar to Dioon holmgrenii De Luca, Sabato & Vázq. Torres, which has a markedly disjunct distribution in Oaxaca. After studying herbarium specimens and making extensive observations on vegetative and reproductive structures from different populations in Oaxaca, we have concluded that the disjunct populations analysed in 2019 represent a distinct and new species of Dioon, separate from the two most phenotypically similar species—namely, D. stevensonii Nic.-Mor. & Vovides and D. holmgrenii. A key to geographically proximal and morphologically similar species as well as to the other species occurring in Guerrero and Oaxaca States is also presented. The proposed new species, Dioon nuusaviorum Mart.-Domínguez, Nic.-Mor. & D.W.Stev., is endemic to Guerrero and inhabits pine and pine-oak forest. Its conservation status, assessed on the based IUCN guidelines and criteria, qualifies as Endangered.
Key words: Cycadales, cycads, Mesoamerica, Neotropics, Sierra Madre del Sur
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| Dioon nuusaviorum sp. nov. A. Ovulate strobilus; B. Megasporophyll; C. Basal scale of megasporophyll; D. Microsporophyll; E. Leaflets variation; F. Cataphylls; G. Seeds variation; H. New leaves; I. Leaves at emergence; J. Leaf at maturity. |
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| Dioon nuusaviorum sp. nov., in habitat. A. Ovuliferous plant in habitat; B. Eumaeus sp; C. Population in La Trinidad; D. Vegetation view; E. Ovulate strobilus at maturity in habitat. |
Dioon nuusaviorum Mart.-Domínguez, Nic.-Mor. & D.W.Stev., sp. nov.
Diagnosis. Dioon nuusaviorum sp. nov. differs from D. holmgrenii by having leaflets imbricate to strongly imbricate, each with three to six long marginal teeth (0.26–0.37 cm long), a margin of the leaflets curved acroscopically, microsporophylls with an acuminate apex and megasporophylls with an apiculate apex. In contrast, D. holmgrenii has non-imbricate leaflets (generally a 0.2–1.0 cm between leaflets) with two to five short teeth on the distal margin (0.15–0.29 cm long), a margin of the leaflets straight, microsporophylls with an acute apex and megasporophylls with an acuminate apex. In comparison to D. stevensonii, this new species differs by its light green leaflets at emergence (vs golden), leaflet imbricate to strongly imbricate (vs not imbricate), acuminate apex of microsporophylls (vs acute), tomentose indument and narrowly-triangular megasporophylls at maturity (vs pubescent at base or scarcely pubescent and triangular).
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| Comparison of leaflets of Dioon holmgrenii, D. stevensonii and Dioon nuusaviorum sp. nov. A. D. stevensonii; B. D. holmgrenii; C. Dioon nuusaviorum sp. nov.; D. D. stevensonii (F. Nicolalde-Morejón et al. 1554, CIB); E. D. holmgrenii (Brigada T. Walters s/n [3997], XAL); F. D. holmgrenii (F. Nicolalde-Morejón et al. 1468, XAL); G. Dioon nuusaviorum sp. nov. (L. Martínez-Domínguez et al. 1745, CIB). |
Lilí Martínez-Domínguez, Fernando Nicolalde-Morejón, Dennis Wm. Stevenson, Francisco G. Lorea-Hernández and Francisco Vergara-Silva. 2026. A striking New Species of Dioon (Zamiaceae) from pine and pine-oak forest of Guerrero, Mexico. PhytoKeys. 274: 229-245. DOI: doi.org/10.3897/phytokeys.274.173907 [11 May 2026]
