Abstract
Dioon Lindley (1843: 59–60) is the best understood of the three cycad genera in Mesoamerica. As such, the appearance of an article published earlier this year in Phytotaxa, claiming to be a revision of the genus, was somewhat surprising. While the article provides a fairly thorough summary of previous work, there is no taxonomic revision. There are also numerous issues/errors (some quite serious) that need to be clarified and/or corrected (see separate Appendix for full list). This correspondence will critique the aforementioned article section by section, beginning with the title and stated goals.
References
Calonje, M., Stevenson, D.W. & Osborne, R. (2020) The World List of Cycads, online edition [Internet]. 2013–2020. [<a href="http://www.cycadlist.org/">http://www.cycadlist.org</a>]
De Luca, P., Sabato, S. & Vázquez Torres, M. (1981) Dioon merolae (Zamiaceae), a new species from Mexico. Brittonia 33 (2): 179–185.
<a href="https://doi.org/10.2307/2806317">https://doi.org/10.2307/2806317</a>
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: 1512–1530.
<a href="https://doi.org/10.1002/ajb2.1149">https://doi.org/10.1002/ajb2.1149</a>
Gregory, T.J. & Chemnick, J. (2004) Hypotheses on the relationship between biogeography and speciation in Dioon (Zamiaceae). In: Walters, T. & Osborne, R. (Eds.) Cycad Classification: Concepts and Recommendations. CABI, Wallingford, UK, pp. 137–148.
Gregory, T.J., Chemnick, J., Salas-Morales, S. & Vovides, A.P. (2003) A new species in the genus Dioon (Zamiaceae) from north-central Oaxaca, Mexico. Botanical Journal of the Linnean Society 141: 471–476.
<a href="https://doi.org/10.1046/j.1095-8339.2003.t01-1-00151.x">https://doi.org/10.1046/j.1095-8339.2003.t01-1-00151.x</a>
Gregory, T., Haynes, J. & Chemnick, J. (2005) Key to the species of Dioon. The Cycad Society. Available from: <a href="http://www.cycadconservation.org/publications/Gregory-et-al-Dioon-Key-2008.pdf">http://www.cycadconservation.org/publications/Gregory-et-al-Dioon-Key-2008.pdf</a> (accessed 25 May 2020)
Gutiérrez-Ortega, J.S., Yamamoto, T., Vovides, A.P., Peréz-Farrera, M.A., Martínez, J.F., Molina-Freaner, F., Watano, Y. & Kajita, T. (2018) Aridification as a driver of biodiversity: a case study for the cycad genus Dioon (Zamiaceae). Annals of Botany 121: 47–60.
<a href="https://doi.org/10.1093/aob/mcx123">https://doi.org/10.1093/aob/mcx123</a>
Haynes, J.L. & Bonta, M.A. (2007) An emended description of Dioon mejiae Standl. & L.O. Williams (Zamiaceae). Proceedings of the 7<sup>th</sup> International Conference on Cycad Biology, Xalapa, Mexico, January 2005. Memoirs of the New York Botanical Garden 97: 418–443.
Lindley, J. (1843) Ornamental flower-garden and shrubbery. Edwards’s Botanical Register 29: misc. 59–60.
Moretti, A., Caputo, P., Cozzolino, S., De Luca, P., Gaudio, L., Siniscalco, G. & Stevenson, D.W. (1993) A phylogenetic analysis of Dioon (Zamiaceae). American Journal of Botany 80 (2): 204–214.
<a href="https://doi.org/10.2307/2445041">https://doi.org/10.2307/2445041</a>
Nicolalde-Morejón, F., Vergara-Silva, F., González-Astorga, J., Vovides, A.P. & Espinosa de los Monteros, A. (2009) Reciprocal illumination of morphological characters upon a molecular hypothesis supports the proposal of a new species of cycad from Mexico. Systematics & Biodiversity 7: 73–79.
<a href="https://doi.org/10.1017/S1477200008002879">https://doi.org/10.1017/S1477200008002879</a>
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 & Succulent Journal 88: 35–42.
<a href="https://doi.org/10.2985/015.088.0104">https://doi.org/10.2985/015.088.0104</a>
Standley, P.C. & Williams, L.O. (1950) Dioon mejiae, a new cycad from Honduras. Ceiba 1: 36–38.
Walters, T. & Osborne, R. (2004) Cycad Classification: Concepts and Recommendations. CABI, Wallingford, UK.
Yáñez, L. (2006) Las Cycadas: biología y conservación en México. Ed. Universidad Autónoma de Chapingo, División de Ciencias Forestales. Mexico. ISBN: 968-02-0277-1
De Luca, P., Sabato, S. & Vázquez Torres, M. (1981) Dioon merolae (Zamiaceae), a new species from Mexico. Brittonia 33 (2): 179–185.
<a href="https://doi.org/10.2307/2806317">https://doi.org/10.2307/2806317</a>
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: 1512–1530.
<a href="https://doi.org/10.1002/ajb2.1149">https://doi.org/10.1002/ajb2.1149</a>
Gregory, T.J. & Chemnick, J. (2004) Hypotheses on the relationship between biogeography and speciation in Dioon (Zamiaceae). In: Walters, T. & Osborne, R. (Eds.) Cycad Classification: Concepts and Recommendations. CABI, Wallingford, UK, pp. 137–148.
Gregory, T.J., Chemnick, J., Salas-Morales, S. & Vovides, A.P. (2003) A new species in the genus Dioon (Zamiaceae) from north-central Oaxaca, Mexico. Botanical Journal of the Linnean Society 141: 471–476.
<a href="https://doi.org/10.1046/j.1095-8339.2003.t01-1-00151.x">https://doi.org/10.1046/j.1095-8339.2003.t01-1-00151.x</a>
Gregory, T., Haynes, J. & Chemnick, J. (2005) Key to the species of Dioon. The Cycad Society. Available from: <a href="http://www.cycadconservation.org/publications/Gregory-et-al-Dioon-Key-2008.pdf">http://www.cycadconservation.org/publications/Gregory-et-al-Dioon-Key-2008.pdf</a> (accessed 25 May 2020)
Gutiérrez-Ortega, J.S., Yamamoto, T., Vovides, A.P., Peréz-Farrera, M.A., Martínez, J.F., Molina-Freaner, F., Watano, Y. & Kajita, T. (2018) Aridification as a driver of biodiversity: a case study for the cycad genus Dioon (Zamiaceae). Annals of Botany 121: 47–60.
<a href="https://doi.org/10.1093/aob/mcx123">https://doi.org/10.1093/aob/mcx123</a>
Haynes, J.L. & Bonta, M.A. (2007) An emended description of Dioon mejiae Standl. & L.O. Williams (Zamiaceae). Proceedings of the 7<sup>th</sup> International Conference on Cycad Biology, Xalapa, Mexico, January 2005. Memoirs of the New York Botanical Garden 97: 418–443.
Lindley, J. (1843) Ornamental flower-garden and shrubbery. Edwards’s Botanical Register 29: misc. 59–60.
Moretti, A., Caputo, P., Cozzolino, S., De Luca, P., Gaudio, L., Siniscalco, G. & Stevenson, D.W. (1993) A phylogenetic analysis of Dioon (Zamiaceae). American Journal of Botany 80 (2): 204–214.
<a href="https://doi.org/10.2307/2445041">https://doi.org/10.2307/2445041</a>
Nicolalde-Morejón, F., Vergara-Silva, F., González-Astorga, J., Vovides, A.P. & Espinosa de los Monteros, A. (2009) Reciprocal illumination of morphological characters upon a molecular hypothesis supports the proposal of a new species of cycad from Mexico. Systematics & Biodiversity 7: 73–79.
<a href="https://doi.org/10.1017/S1477200008002879">https://doi.org/10.1017/S1477200008002879</a>
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 & Succulent Journal 88: 35–42.
<a href="https://doi.org/10.2985/015.088.0104">https://doi.org/10.2985/015.088.0104</a>
Standley, P.C. & Williams, L.O. (1950) Dioon mejiae, a new cycad from Honduras. Ceiba 1: 36–38.
Walters, T. & Osborne, R. (2004) Cycad Classification: Concepts and Recommendations. CABI, Wallingford, UK.
Yáñez, L. (2006) Las Cycadas: biología y conservación en México. Ed. Universidad Autónoma de Chapingo, División de Ciencias Forestales. Mexico. ISBN: 968-02-0277-1