Ceratozamia whitelockiana

Ceratozamia whitelockiana is a cycad of northern Oaxaca, in southern Mexico, endemic to the Sierra Norte in the region of La Chinantla, where it grows in the shade of mountain tropical forests. This species of the genus Ceratozamia, described in 1995 by two Californian cycad growers, has few but very large leaves, 2 m long or more, on a long petiole with few prickles, glaucous pea green when young. It is listed as Endangered by the IUCN.

Key facts about Ceratozamia whitelockiana

  • Accepted name: Ceratozamia whitelockiana Chemnick & T.J.Greg. (journal issue dated 1995, published in 1996), 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; “Whitelock’s horncone” in the Gymnosperm Database
  • Natural range: Mexico, Sierra Norte of Oaxaca (La Chinantla); 335 to 975 m according to the original description, 500 to 1,800 m according to the 2022 monograph
  • IUCN status: Endangered (EN, criteria A2c; B1ab(i,ii,iii,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, deeply shaded slopes in primary forest, on stony clay or karst rocks; turns yellow and pale in full sun
  • Habit and adult size: solitary trunk, partly buried, 20 to 80 cm long and 12 to 30 cm across; 2 to 10 leaves 1.3 to 2.5 m long
  • In the UK, US and Australia: declared by two Californian 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 whitelockiana

The original description (Chemnick and Gregory, 1995) singles it out by its few large, upright, glaucous pea-green leaves on a very long petiole, and by its relatively small male and female cones. Its main measurements are as follows:

  • Trunk: solitary, even in cultivation, partly buried, cylindrical, 20 to 30 cm tall and 12 to 18 cm across, reddish brown and rough (up to 80 cm long and 30 cm across, and lying down, according to the 2022 monograph).
  • Leaves: 2 to 5 according to the original description (3 to 10 according to the monograph), 2 to 2.5 m long, produced in flushes of 2 to 4, glaucous and light pea green when young, mid-green later; petiole 1 to 1.25 m long, with few prickles (3 to 22, according to the monograph); rachis unarmed.
  • Leaflets: 30 to 40 pairs, linear-lanceolate to sickle-shaped, papery, 30 to 50 cm long and 3 to 3.8 cm wide, with slightly rolled margins.
  • Male cones: elongated, 26 to 28 cm long and 1.5 to 2.8 cm across.
  • Female cones: cylindrical to ovoid, 14 to 18 cm long and 7.5 to 10 cm across, with a stout terminal point, on a short stalk 3 to 3.8 cm long.
  • Seeds: 3.1 to 3.3 cm long and 2.5 to 2.7 cm across, with white flesh turning brown.

The 2022 monograph describes leaves that hang down rather than stand upright, 20 to 48 pairs of lance-shaped leaflets 2 to 3.7 cm wide, male cones 20 to 30 cm long on a stalk 15 to 25 cm long, and seeds 2.1 to 2.7 cm long. It also contradicts itself on the female cone stalk: its description gives 1 to 4 cm, in line with the original description, but its discussion gives 12 to 23 cm and attributes a short stalk to Ceratozamia mixeorum, whereas other authors describe very long stalks in that species (Pérez-Farrera and colleagues, 2022). The detailed description of the monograph and the original description therefore agree on a short stalk.

Hybrids

No natural or garden hybrid has been documented.

Possible confusion

The most likely confusion is with its closest relative, Ceratozamia miqueliana, but other large neighbouring species also resemble it:

  • Ceratozamia miqueliana, the closest species according to the describers: same trunk, same glaucous pea-green young leaves and cones of similar size; but 7 to 10 leaves with much broader leaflets (6 to 6.5 cm) that are fewer (about fifteen pairs), and a petiole heavily armed with long curved prickles. The nearest population of Ceratozamia miqueliana lies about 150 km away.
  • Ceratozamia mixeorum, of the neighbouring Sierra Mixe: similar foliage, but a petiole with more than 28 prickles (Martínez-Domínguez and colleagues, 2022).
  • Ceratozamia mexicana and Ceratozamia robusta, to which some populations of northern Oaxaca had been referred: many dark green, heavily armed leaves and much larger cones (Chemnick and Gregory, 1995).

In the key of the 2022 monograph, green to yellowish-green new leaves and an unarmed rachis lead to Ceratozamia whitelockiana. Without a cone, a Ceratozamia is hard to tell from a Zamia.

Taxonomy

Ceratozamia whitelockiana 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 south-western Mexico. It has no synonym. It was published by Jeffrey Chemnick and Timothy Gregory, of Santa Barbara (California), in the July 1995 issue of the journal Phytologia, which appeared in 1996 according to The World List of Cycads. The authors criticised a taxonomy of the genus they called “confused, ambiguous and incomplete”, which lumped many isolated populations under three vague names (Ceratozamia mexicana, Ceratozamia robusta and Ceratozamia latifolia).

They placed their species close to Ceratozamia miqueliana and Ceratozamia euryphyllidia, in a “miqueliana group”. The phylogeny of Habib and colleagues (2023), based on nearly 4,000 nuclear genes, confirmed its place in the Ceratozamia miqueliana complex, within the large Miqueliana clade; in the coalescent analyses, Ceratozamia whitelockiana is the sister of all the other species of that group. The 1995 authors also noted that the species keeps its own appearance even after long cultivation under varied conditions, next to Ceratozamia mexicana and Ceratozamia robusta.

The type

The type caused a problem. The holotype announced at the herbarium of the Huntington Botanical Gardens (HNT) is probably lost, and the duplicate intended for the XALU herbarium cannot be found. In 2023, Jody Haynes therefore designated the duplicate at the herbarium of Fairchild Tropical Botanic Garden (FTG) as the lectotype, and the one at the Santa Barbara Botanic Garden herbarium (SBBG) as the isolectotype (as reported by The World List of Cycads).

Etymology and history

The epithet honours Loran M. Whitelock (1930–2014), of Los Angeles, a leading student and collector of cycads, for his dedication and contribution to cycad biology and awareness worldwide (Haynes, 2022). He had provided the authors with the cone measurements.

The type (Chemnick & Gregory 5) was collected in May 1995 south of Valle Nacional, in the municipality of San Juan Bautista Valle Nacional. The authors had known the population for a long time: they had visited it several times in 1979, 1980 and 1981, and had been growing it for more than fourteen years by 1995. Living plants were then kept at Ganna Walska Lotusland (Santa Barbara), at the Mildred E. Mathias Botanical Garden of the University of California, Los Angeles, and in the greenhouses of the University of California, Santa Barbara. The species is also in the collection of Nong Nooch Tropical Botanical Garden in Thailand, which supplied the material for the 2023 phylogenetic study.

Common names

No traditional name is recorded, and the 2022 monograph lists no local name. The Gymnosperm Database uses the English name “Whitelock’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

According to the original description, Ceratozamia whitelockiana was known only from the basin of the Río Valle Nacional, in mountain tropical forest between 335 and 975 m, and mostly at low elevation (335 to 600 m). It grows on very steep, heavily shaded east- and west-facing slopes, in primary forest, with Chamaedorea and Geonoma palms, figs, begonias and spikemosses, on a light, crumbly, stony clay with outcrops of sedimentary rock.

The 2022 monograph widens this picture: it describes the species as endemic to the Sierra Norte of Oaxaca, in the region of La Chinantla, between 500 and 1,800 m, along the gradient from evergreen tropical forest with oaks to cloud forest with Oreomunnea mexicana, on karst rocks. Its specimens come from the municipalities of Ixtlán de Juárez, San Felipe Usila, San Juan Bautista Valle Nacional, San Juan Juquila Vijanos, San Pedro Sochiapam, San Juan Tepeuxila and Santiago Comaltepec.

The 1995 authors observed that the species does not persist for long in open ground or secondary forest: the only plants found in cleared areas were kept by farmers and had discoloured, yellow, chlorotic foliage. No pollination study specific to the species has been published.

Conservation status and regulation

Ceratozamia whitelockiana is listed as Endangered (EN, criteria A2c; B1ab(i,ii,iii,v)) on the IUCN Red List, in an assessment by J.D. Bösenberg published in 2022 (status given by The World List of Cycads and confirmed by the Red List data distributed through GBIF, 30 October 2026); the 2022 monograph cites the same category with additional criteria (B2ab(i,ii,iii,v) and C1). As early as 1995 its describers considered it threatened: in three days of fieldwork in May 1995 they counted about 250 plants, perhaps half as many as in 1979–1981; the forests of the basin were being cleared and burnt for coffee, bananas and crops, and the smoke from the burning was intense. They judged habitat destruction far more serious than collecting, as the species was rare in collections.

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, ask for seed-grown plants with documents of origin. This general information does not replace the official texts: check the regulations in force before buying, importing or exchanging plants.

Growing Ceratozamia whitelockiana

The only cultivation information comes from its describers, who grew it in California for more than fourteen years: the trunk stays solitary in cultivation, and the plant keeps its own appearance whatever the conditions. Its behaviour in open ground in the wild gives one clear piece of advice: it is a shade plant.

  • Light: shade or partial shade; in full sun, wild plants left in clearings turn yellow and pale.
  • Soil: free-draining, clayey and stony or rich in humus, without standing water.
  • Watering: regular during growth, as in its lowland mountain forest; reduced in winter.
  • Space: adult leaves exceed 2 m; allow headroom.

Outdoor and in-ground cultivation

No outdoor planting with a dated result has been published. The describers did not say whether their Californian plants grew outdoors or under glass; one of the three collections they cited was a greenhouse collection.

Container cultivation

Young plants can be grown in a pot in a free-draining, humus-rich mix and kept in shade, which allows them to be moved under cover in winter; adults, with leaves over 2 m long, need a large container.

In cultivation in the UK, US and Australia

In the United States, BGCI PlantSearch (queried on 30 October 2026) lists Ganna Walska Lotusland (Santa Barbara) and the Huntington (San Marino), both in California; the online catalogue of Montgomery Botanical Center (Coral Gables, Florida) lists two accessions. No garden in the United Kingdom or Australia declares it. Outside these countries, BGCI lists the Marimurtra botanic garden in Blanes (Catalonia, Spain), the Francisco Javier Clavijero Botanic Garden in Xalapa and the Ethnobotanical Garden of Oaxaca, in Mexico. No garden states whether its plants grow outdoors.

Propagation

Propagation is from seed, since the trunk does not produce offsets, even in cultivation, according to its describers. 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 whitelockiana has been documented. In cultivated Ceratozamia, growers mainly report rot in cold, sodden soil and leaf scorch after sudden exposure to full sun; in the wild, its describers saw plants left in clearings turn yellow and chlorotic.

Cold hardiness

No data exist for Ceratozamia whitelockiana: no dated cultivation report, and no temperature record for its sites. Its describers grew it in California but published no minimum temperatures.

Mediterranean and European experience

No cultivation of this species has been reported in France, and the Jardin zoologique tropical in La Londe-les-Maures (Var, on the French Riviera) has published no observation of it. In Spain, BGCI lists the Marimurtra botanic garden on the Costa Brava, without saying whether the plant grows outdoors or under glass.

United Kingdom, United States and Australia

No dated cold record and no commercial hardiness rating have been published. A plant of lowland mountain tropical forest, it is best kept frost-free, under glass or indoors in cold regions, until documented trials exist.

Toxicity and precautions

No toxicity study specific to Ceratozamia whitelockiana 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 1995 authors only mention a few plants kept by farmers in cleared plots.

Frequently asked questions

Who was Whitelock?

Loran M. Whitelock (1930–2014), a cycad collector from Los Angeles. A leading expert on cycads, he provided the describers with the cone measurements of the species, which was named after him.

Where does it grow?

In northern Oaxaca, Mexico. It lives in the Sierra Norte, in the region of La Chinantla, in heavily shaded mountain tropical forest and cloud forest, between about 335 and 1,800 m depending on the source.

How can I recognise it?

By its few large leaves. They are 2 m long or more, carried on a very long petiole with few prickles, and glaucous pea green when young. Its cones are small for a plant of this size.

Does it tolerate sun?

No, according to field observations. Its describers saw plants left in clearings turn yellow and pale. Grow it in shade or partial shade.

Is it endangered?

Yes. The IUCN lists it as Endangered, and Mexico as in danger of extinction. As early as 1995, its describers estimated that the population might have halved in about fifteen years because of clearing and burning.

Can it take frost?

Nobody knows. No dated trial and no temperature record have been published. Keep it frost-free.

Further reading on Succulentes

Sources

Reference sites

Bibliography

  • Chemnick, J. & Gregory, T.J. (1995, published 1996). A new species of Ceratozamia (Zamiaceae) from Oaxaca, Mexico with comments on distribution, habitat, and relationships. Phytologia 79(1): 51–57. [Original description; primary source.]
  • 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.]
  • Haynes, J.L. (2023). Critical review of “Monograph of Ceratozamia (Zamiaceae, Cycadales): an endangered genus” published in PhytoKeys 208: 1–102 (2022). Phytotaxa 612(2): 159–200. https://doi.org/10.11646/phytotaxa.612.2.4 [Critique of the monograph; lectotypification reported by The World List of Cycads.]
  • Pérez-Farrera, M.A., Gutiérrez-Ortega, J.S., Gregory, T.J., Chemnick, J., Salas-Morales, S., Calonje, M. & Díaz-Jiménez, P. (2022). Ceratozamia schiblii (Zamiaceae): a new cycad species from the eastern mountains of Oaxaca, Mexico. Taxonomy 2(3): 324–338. https://doi.org/10.3390/taxonomy2030025 [Peduncles of Ceratozamia mixeorum; 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.]
  • Bösenberg, J.D. (2022). Ceratozamia whitelockiana. The IUCN Red List of Threatened Species 2022: e.T42128A69865109. https://doi.org/10.2305/IUCN.UK.2022-1.RLTS.T42128A69865109.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.]