Ceratozamia zaragozae

Ceratozamia zaragozae is a small cycad of Mexico, endemic to an isolated mountain range of San Luis Potosí, in the municipalities of Rioverde and Zaragoza, where it grows in pine-oak forest between about 1,500 and 1,950 m (about 4,920 to 6,400 ft). This species of the genus Ceratozamia, described in 1963, is recognised by its leaves with a twisted, completely spineless petiole and rachis, bearing very narrow leaflets. Long regarded as one of the most threatened cycads of Mexico, it has been listed as Endangered by the IUCN since 2022, following a field study published in 2018.

Key facts about Ceratozamia zaragozae

  • Accepted name: Ceratozamia zaragozae Medellín (1963), the author also cited as Medellín-Leal; accepted by The World List of Cycads (version 2026.08.15), by the 2022 monograph of the genus and by the World Checklist of Vascular Plants (WCVP, the database behind POWO, read via GBIF)
  • Former names and synonyms: none
  • Family: Zamiaceae, order Cycadales
  • Common names: no traditional name; “Zaragoza’s horncone” in the Gymnosperm Database
  • Natural range: Mexico, San Luis Potosí, a small mountain range in the municipalities of Rioverde and Zaragoza; 1,500 to 1,950 m according to the 2022 monograph, which also cites a specimen collected at 2,031 m
  • IUCN status: Endangered (EN, criterion B1ab(v)), assessment published in 2022
  • CITES and other protection: CITES Appendix I (whole genus, since 1985); Annex A in the European Union, seeds included; “in danger of extinction” (P) in the Mexican standard NOM-059-SEMARNAT-2010
  • Documented hardiness: no data for the species (see Cold hardiness)
  • Light and soil: in the wild, shaded understorey of pine-oak forest, on soils derived from volcanic rock (rhyolite) or on karst rocks depending on the source; no published growing advice
  • Habit and adult size: trunk partly buried, 10 to 20 cm long and 10 to 15 cm across; 3 to 27 leaves 95 to 202 cm long according to the 2022 monograph, leaves 20 to 95 cm long according to the original description
  • In the UK, US and Australia: declared by six American gardens; none in the UK or Australia (see In cultivation)
  • Toxicity: no data for the species; treat it as poisonous, like all cycads (see Toxicity and precautions)

How to recognise Ceratozamia zaragozae

Its clearest character is the twisted petiole and rachis, without a single prickle, carrying linear leaflets only 4 to 7 mm wide, thin and strongly rolled inwards. The 2022 monograph describes it as follows:

  • Trunk: partly buried, upright, 10 to 20 cm long and 10 to 15 cm across.
  • Leaves: 3 to 27, 95 to 202 cm long, ascending, reddish brown with whitish-grey hairs at emergence, hairless later; petiole 11 to 36 cm and rachis 40 to 77 cm long, both twisted and unarmed.
  • Leaflets: 25 to 46, linear, membranous, strongly rolled inwards, 17 to 31.5 cm long and 0.4 to 0.7 cm wide, with yellow articulations.
  • Male cones: cylindrical, 15 to 19 cm long and 2 to 3.5 cm across, greenish then reddish brown.
  • Female cones: cylindrical, 7 to 12 cm long and 5.5 to 7.3 cm across, dark green when mature, on a stalk 6 to 9 cm long.
  • Seeds: oval, 2 to 2.8 cm long, light brown when mature.

The original description (Medellín-Leal, 1963) describes more modest plants: an ovoid or subcylindrical trunk 9 to 20 cm tall and 9 to 11 cm across; leaves 20 to 95 cm long, widely spaced, hairy when young then hairless, irregularly twisted to the right or to the left, with 16 to 43 pairs of leaflets; petiole and rachis entirely unarmed; leaflets linear-lanceolate, straight or slightly sickle-shaped, leathery, with entire, slightly rolled margins, shinier and darker above, 5 to 28 cm long and 3 to 10 mm wide, with 4 to 10 veins; a subcylindrical, pointed male cone 10 to 20 cm long on an unarmed stalk 9 to 14 cm long; a subcylindrical female cone 8 to 12 cm long and 6 to 7 cm across, on a stalk about 9 cm long, with hairless, irregular scales and very small upright horns; and roughly spherical seeds about 2 cm across, irregularly but clearly ribbed. It therefore differs from the monograph in the texture of the leaflets (leathery rather than membranous) and the shape of the seeds (almost spherical rather than oval). Jones (1993), as cited by the Gymnosperm Database, also gives 2 to 5 leaves in the wild.

Hybrids

No natural or garden hybrid has been documented.

Possible confusion

The twisted rachis is found in only one other species of the genus, but several small species of north-eastern Mexico also have narrow leaflets:

  • Ceratozamia norstogii, of Chiapas and Oaxaca: rachis also twisted, but petiole armed with many stout prickles, and leathery leaflets (Martínez-Domínguez and colleagues, 2022).
  • Ceratozamia sabatoi, of the Sierra Gorda: flat, broader leaflets (6 to 15 mm), petiole armed with small prickles and straight rachis.
  • Ceratozamia kuesteriana, of Tamaulipas: broader, channelled leaflets and a coppery petiole.
  • Ceratozamia hildae, also present in San Luis Potosí: leaflets grouped in pairs or small clusters along the rachis.

Without a cone, a Ceratozamia is hard to tell from a Zamia; the two small horns on the cone scales settle the question.

Taxonomy

Ceratozamia zaragozae is accepted by The World List of Cycads, by the 2022 monograph and by the WCVP, the database behind POWO (read via GBIF on 30 October 2026), which records it from north-eastern Mexico. It has no synonym. The species was described in 1963 by Fernando Medellín-Leal, of the Instituto de Investigación de Zonas Desérticas of the Autonomous University of San Luis Potosí, in the journal Brittonia (15: 175–176, April 1963). He had collected it during an excursion in the south of the state with Elwood Molseed and Myron Kimnach, of the University of California, and his text was translated from Spanish by Rogers McVaugh. The World List of Cycads gives the author as “Medellín”; other sources write “Medellín-Leal”.

Medellín-Leal saw affinities with Ceratozamia kuesteriana and Ceratozamia matudae, and separated his species from all others by the complete absence of prickles, the irregular but constant twisting of the leaves, the very small horns of the scales, the irregular scales of the female cone and the almost spherical seeds.

The phylogeny of Habib and colleagues (2023) places it in the kuesteriana subclade, with Ceratozamia sabatoi, its sister species, and Ceratozamia kuesteriana. This group of small, narrow-leaved species of north-eastern Mexico belongs to the large Mexicana clade. According to Vovides and colleagues (2016), earlier molecular studies (González and Vovides, 2002 and 2012) had already recognised a complex of species around Ceratozamia zaragozae, north of the Trans-Mexican Volcanic Belt. In the 2024 study of the evolution of the cones of the genus, its male cones are among the most distinct and its female cones among the most reduced.

Etymology and history

The epithet honours General Ignacio Zaragoza (1829–1862), who defeated the French army at the Battle of Puebla on 5 May 1862. The original description says so explicitly: the species was dedicated to General Zaragoza on the first centenary of his “glorious deeds in defence of national sovereignty”, as The World List of Cycads also reports from the etymological compendium of Haynes (2022).

The type is a female plant collected on 22 July 1962 by Medellín-Leal (no. 1452) in the municipality of Rioverde, at about 1,800 m. The holotype is kept in the SLPM herbarium in San Luis Potosí, with duplicates in several Mexican and American herbaria (ENCB, GH, MEXU, MICH, US). The original description also cites a male plant (Medellín-Leal 1451). The species is grown, but rarely, as an ornamental (Jones, 1993, as cited by the Gymnosperm Database), and it is in the collection of Nong Nooch Tropical Botanical Garden in Thailand, where the samples for the 2023 phylogenetic study were taken.

Common names

No traditional name is recorded, and the 2022 monograph lists no local name in Mexico. The Gymnosperm Database uses the English name “Zaragoza’s horncone”, built on the pattern it applies to every species of the genus; it is a book name, not a name in common use.

In the wild

Ceratozamia zaragozae lives in a small mountain range of south-central San Luis Potosí, in pine-oak forest. The sources disagree on the substrate: the 2022 monograph places it on karst rocks between 1,500 and 1,950 m, whereas the original description puts the type on a slope of rhyolite, a volcanic rock, in pine-oak forest at 1,800 m, as does Jones (1993) after it. The monograph lists collections from the municipalities of Rioverde and Zaragoza, one of them at 2,031 m.

A field study by Castillo-Lara, Octavio-Aguilar and De-Nova (2018) described the structure and spatial distribution of its populations. According to the 2022 monograph, which reports its results, densities vary widely, from 4 to 209 plants per 2,500 m², but population growth is low; the authors suggested moving the species from Critically Endangered to Endangered. No pollination study specific to the species has been published.

Conservation status and regulation

Ceratozamia zaragozae is listed as Endangered (EN, criterion B1ab(v)) on the IUCN Red List, in an assessment by J.D. Bösenberg published in 2022: its range is very small and the number of mature individuals is declining (status given by The World List of Cycads and confirmed by the Red List data distributed through GBIF, 30 October 2026). The 2022 monograph still cited an earlier assessment as Critically Endangered (CR) and recalled that the 2018 field study proposed downgrading it to Endangered, which the 2022 assessment did. Jones (1993) attributed its decline to illegal collecting.

In Mexico, the species is listed as “in danger of extinction” (P), as an endemic species, in the standard NOM-059-SEMARNAT-2010, in the list as modified on 14 November 2019. Like the whole genus, it has been covered by CITES Appendix I since 1 August 1985 (cycads had been in Appendix II since 1977), and by Annex A of Regulation (EC) No 338/97 in the European Union (annexes now set by Regulation (EU) 2026/1383, applicable since 29 June 2026), seeds included; Species+ lists it under its own name (checked on 30 October 2026). International trade in wild-collected plants for commercial purposes is banned; only artificially propagated plants with the required permits can be traded.

In practice, buy only seed-grown plants with documents of origin: a species with such small populations cannot sustain any collecting. This general information does not replace the official texts: check the regulations in force before buying, importing or exchanging plants.

Growing Ceratozamia zaragozae

No source describes the cultivation of this rarely grown species in detail. The pointers below are drawn from its habitat and from the general rules for the genus; they have not been confirmed by published trials.

  • Light: partial shade or light shade, like its pine-oak understorey; avoid hot afternoon sun.
  • Soil: very free-draining and mineral, with a little organic matter; its habitat combines volcanic or limestone rock with forest humus.
  • Watering: regular and moderate during growth, much reduced in winter; with its partly buried trunk, the plant dislikes standing water.
  • Growth: slow; no figures specific to the species have been published.

Outdoor and in-ground cultivation

No outdoor planting of Ceratozamia zaragozae has been documented with a dated result. The American gardens that declare it, in California, Florida and Missouri, do not say whether their plants grow outdoors or under glass.

Container cultivation

A small species with a short trunk, it is suited to pot culture in a mineral, free-draining mix, which allows it to be moved under cover in winter.

In cultivation in the UK, US and Australia

In the United States, BGCI PlantSearch (queried on 30 October 2026) lists six gardens: Ganna Walska Lotusland (Santa Barbara), the San Diego Zoo Botanical Gardens, the Huntington (San Marino) and the University of California Botanical Garden at Berkeley in California, Montgomery Botanical Center (Coral Gables) in Florida, and the Missouri Botanical Garden (St. Louis). The online catalogue of Montgomery Botanical Center lists four accessions. No garden in the United Kingdom or Australia declares it. Outside these countries, BGCI lists four gardens in Mexico, the Jardin des Plantes in Paris and a garden in China. No garden states whether its plants grow outdoors.

Propagation

Propagation is from seed. The plants are male or female: both sexes and, in cultivation, hand pollination are needed to obtain fertile seed. No germination data specific to the species have been published. Handle seeds wearing gloves.

Pests and diseases

No pest or disease specific to Ceratozamia zaragozae has been documented. In cultivated Ceratozamia, growers mainly report rot in cold, sodden soil and leaf scorch after sudden exposure to full sun.

Cold hardiness

No data exist for Ceratozamia zaragozae: no dated cultivation report, and no temperature record published for its sites. Its altitude, among the highest in the genus, is not enough on its own to infer any frost tolerance.

Mediterranean and European experience

No outdoor cultivation of this species has been reported in Europe, and the Jardin zoologique tropical in La Londe-les-Maures (Var, on the French Riviera) has published no observation of it. The Jardin des Plantes in Paris declares it to BGCI without saying where it is grown.

United Kingdom, United States and Australia

No dated cold record and no commercial hardiness rating have been published. Overwinter it frost-free until documented trials exist.

Toxicity and precautions

No toxicity study specific to Ceratozamia zaragozae has been published. The risk is well documented in other cycads: their tissues, and above all their seeds, contain toxic glycosides (cycasin, macrozamin), from which methylazoxymethanol is derived, a compound harmful to the liver and nervous system. In the absence of evidence to the contrary, treat the plant as poisonous: keep seeds and leaves out of reach of children and animals, wear gloves to clean seeds, and if any part is swallowed, call a poison centre, a doctor or a vet straight away.

Traditional uses

No traditional use is known; the 2022 monograph records none. The species is only grown, rarely, as an ornamental.

Frequently asked questions

Who was Zaragoza?

The Mexican general Ignacio Zaragoza. He defeated the French army at Puebla on 5 May 1862, and the species was dedicated to him a century later, in 1963.

Where does it grow?

Only in San Luis Potosí, Mexico. It is found in a small mountain range in the municipalities of Rioverde and Zaragoza, in pine-oak forest, between about 1,500 and 2,000 m.

Is it the most threatened cycad of Mexico?

Not any more, according to the Red List. The 2022 monograph still cited an assessment as Critically Endangered; a 2018 field study proposed downgrading it to Endangered, the category adopted in 2022. It remains rare and very localised.

How can I recognise it?

By its twisted, spineless rachis. Its very narrow leaflets, 4 to 7 mm wide, are thin and rolled. Only Ceratozamia norstogii also has a twisted rachis, but its petiole is very prickly.

Can it take frost?

Nobody knows. No dated cultivation trial and no temperature record for its habitat have been published. Overwinter it frost-free until data exist.

Is it poisonous?

It should be assumed so. No analysis exists for the species or for the genus, but the seeds of the cycads that have been studied contain toxins that seriously harm the liver and nervous system.

Further reading on Succulentes

Sources

Reference sites

Bibliography

  • Medellín-Leal, F. (1963). A new species of Ceratozamia from San Luis Potosí. Brittonia 15(2): 175–176. https://doi.org/10.2307/2805404 [Original description: Latin diagnosis, description, type, habitat, affinities, dedication. Primary source.]
  • Castillo-Lara, P., Octavio-Aguilar, P. & De-Nova, J.A. (2018). Ceratozamia zaragozae Medellín-Leal (Zamiaceae), an endangered Mexican cycad: new information on population structure and spatial distribution. Brittonia 70(2): 155–165. https://doi.org/10.1007/s12228-017-9513-1 [Population structure and distribution; results cited from the 2022 monograph.]
  • Martínez-Domínguez, L., Nicolalde-Morejón, F., Vergara-Silva, F. & Stevenson, D.W. (2018). Taxonomic review of Ceratozamia (Zamiaceae) in the Sierra Madre Oriental, Mexico. PhytoKeys 100: 91–124. https://doi.org/10.3897/phytokeys.100.23152 [Regional review; open access.]
  • Martínez-Domínguez, L., Nicolalde-Morejón, F., Vergara-Silva, F. & Stevenson, D.W. (2022). Monograph of Ceratozamia (Zamiaceae, Cycadales): an endangered genus. PhytoKeys 208: 1–102. https://doi.org/10.3897/phytokeys.208.80382 [Monograph of the genus; open access.]
  • Martínez-Domínguez, L., Nicolalde-Morejón, F., Vergara-Silva, F., Gernandt, D.S., Huesca-Domínguez, I. & Stevenson, D.W. (2024). Evolutionary trends of reproductive phenotype in Cycadales: an analysis of morphological evolution in Ceratozamia. Annals of Botany 134(4): 631–650. https://doi.org/10.1093/aob/mcae058 [Evolution of the cones in the genus; open access.]
  • Habib, S., Gong, Y., Dong, S., Lindstrom, A., Stevenson, D.W., Wu, H. & Zhang, S. (2023). Phylotranscriptomics shed light on intrageneric relationships and historical biogeography of Ceratozamia (Cycadales). Plants 12(3): 478. https://doi.org/10.3390/plants12030478 [Phylogeny of the genus, material from Nong Nooch Tropical Botanical Garden; open access.]
  • Vovides, A.P., Stevenson, D.W., Pérez-Farrera, M.A., López, S. & Avendaño, S. (2016). What is Ceratozamia mexicana (Zamiaceae)? Botanical Sciences 94(2): 419–429. https://doi.org/10.17129/botsci.449 [Summary of earlier molecular studies; open access.]
  • Jones, D.L. (1993). Cycads of the World. Reed, Chatswood. [Description, habitat; cited from the Gymnosperm Database.]
  • Bösenberg, J.D. (2022). Ceratozamia zaragozae. The IUCN Red List of Threatened Species 2022: e.T42103A69867344. https://doi.org/10.2305/IUCN.UK.2022-1.RLTS.T42103A69867344.en [Red List assessment; category confirmed by GBIF.]
  • Haynes, J.L. (2022). Etymological compendium of cycad names. Phytotaxa 550(1): 1–31. https://doi.org/10.11646/phytotaxa.550.1.1 [Source of the etymologies given by The World List of Cycads.]
  • Calonje, M., Stevenson, D.W. & Osborne, R. (2026). The World List of Cycads, version 2026.08.15. Montgomery Botanical Center, Coral Gables. https://doi.org/10.5281/zenodo.21958524 [Reference checklist.]