Zamia dressleri

Zamia dressleri is a cycad endemic to Panama, known from the province of Colón and the Kuna comarca of Guna Yala, on the Caribbean side of the country. This species of the genus Zamia, described in 1993, has an underground stem and usually a single leaf with a few huge, pleated leaflets; its new leaves flush reddish to mahogany. Prized by collectors but reputed difficult to grow, it is rated Endangered by the IUCN.

Key facts about Zamia dressleri

  • Accepted name: Zamia dressleri D.W.Stev. (1993), accepted by The World List of Cycads (version 2026.08.15) and by GBIF; POWO could not be consulted directly
  • Former names and synonyms: none
  • Family: Zamiaceae, order Cycadales
  • Common names: no name attested
  • Natural range: Panama: province of Colón and comarca of Guna Yala; only two small, separate populations were known in 1993
  • IUCN status: Endangered (EN), criteria B1ab(iii,v), assessment published in 2022
  • CITES and other protection: CITES Appendix II (whole genus, since 1977; seeds exempt under annotation #4); Annex B in the European Union
  • Documented hardiness: no measured data; growers stress that it needs warmth day and night all year (see Cold hardiness)
  • Light and soil: lowland tropical rainforest on heavy soils; the type was collected at 300 m; in cultivation, filtered light, excellent drainage and high humidity
  • Habit and adult size: underground stem 3 to 5 cm across in the original description; usually one leaf (two or three at most) 0.5 to 1.5 m long, with 2 to 5 pairs of pleated leaflets 30 to 50 cm by 12 to 15 cm
  • In the UK, US and Australia: Montgomery Botanical Center (Florida) lists two accession numbers; also declared to BGCI by Marie Selby Botanical Gardens, the Huntington, San Diego Botanic Garden, the Atlanta Botanical Garden and the New York Botanical Garden; no British or Australian record
  • Toxicity: no data specific to the species; treat it as poisonous, like all cycads (see Toxicity and precautions)

How to recognise Zamia dressleri

Look for a Zamia with an underground stem that almost always produces a single leaf, with very large leaflets deeply grooved between the veins, which gives them a pleated look. The measurements below come from the original description (Stevenson, 1993, page 6, figure 3):

  • Stem: underground, 3 to 5 cm in diameter; cataphylls ovate, 1 to 2 cm long and 2 to 3 cm wide.
  • Leaves: usually one (sometimes two or three), 0.5 to 1.5 m long; petiole 0.3 to 1 m, sparsely to densely prickly; rachis with 2 to 5 pairs of leaflets, sometimes with a few prickles in its lower third.
  • Leaflets: stalkless, elliptic, grooved between the veins on the upper side, wedge-shaped at the base, acuminate, toothed in the upper third; the large middle leaflets are 30 to 50 cm long and 12 to 15 cm wide.
  • Male cones: cream to tan, cylindrical to elongate-cylindrical, 5 to 8 cm long and 1 to 2 cm across.
  • Female cones: wine red to dark reddish brown, ovoid-cylindrical, shortly stalked, 10 to 15 cm long and 3 to 4 cm across.
  • Seeds: red, ovoid, 1 to 1.5 cm in diameter.

In the introduction of the same paper, however, Stevenson gives the species 4 to 8 pairs of very broad leaflets, against 2 to 5 in the description. Field observers and growers add further details. Jay Vannini, a naturalist who grows Central American cycads in the United States and Guatemala, describes an elongated underground caudex; young plants carry one or two leaves with two to four pairs of large pleated leaflets, while older plants hold up to three leaves about 1.85 m (6 ft) long with five or six pairs of very large leaflets; new flushes are a handsome mahogany or orange-brown (Vannini, 2019). The Californian nursery Jungle Music describes red-brown new leaves and leaflets 10 to 15 cm (4 to 6 in) wide and 30 to 45 cm (1 to 1.5 ft) long, thinner than the corrugated leaflets of Zamia skinneri. A photograph taken in Colón province in 1999 and published in the Virtual Cycad Encyclopedia of the Palm & Cycad Societies of Florida also shows a reddish young leaf.

Hybrids

No hybrid has been documented.

Possible confusion

Several Zamia with large or pleated leaflets grow in Panama and Colombia:

  • Zamia wallisii, from northern Colombia (Antioquia), the species Stevenson (1993) considered closest: a solitary leaf and 2 to 5 pairs of very large grooved leaflets, but leaflets borne on a grooved stalklet, and ovoid male cones.
  • Zamia amplifolia, from Colombia, also has very broad grooved leaflets; a French grower who had seen both in the wild found them “very, very similar”. In its commentary on Zamia amplifolia, the Flora de Colombia recalls that Norstog and Nicholls (1997) pointed out the similarity between Zamia wallisii and Zamia dressleri. The two species live in different countries.
  • The species of the Zamia skinneri group, also with pleated leaflets (Zamia skinneri, Zamia imperialis, Zamia neurophyllidia, Zamia hamannii), usually have more leaves and smaller leaflets; in Stevenson’s key (1993), Zamia skinneri is separated from Zamia dressleri by its aerial stem, up to 2 m tall, and its more numerous leaves.
  • Zamia cunaria, found in the same provinces of eastern Panama, has smooth, narrower leaflets (5 to 8 cm) in greater number (3 to 12 pairs) (Stevenson, 1993).

Taxonomy

Zamia dressleri is an accepted name according to The World List of Cycads and GBIF; POWO could not be consulted directly. It was described by Dennis W. Stevenson in 1993, in his revision of the Zamiaceae of Panama published in Brittonia (45: 1-16), together with Zamia cunaria, Zamia ipetiensis and Zamia neurophyllidia. The type specimen (D.W. Stevenson, I. Valdespinos and H. Herrera 1145) was collected on 7 January 1989 in Colón province, at 300 m; the holotype is kept at the New York Botanical Garden (NY), with isotypes at FTG, MO, NY, PMA and U. The name has not changed since.

In his Latin diagnosis, Stevenson compares the species with Zamia wallisii, from which it differs in its stalkless leaflets. In the biogeographic part of the same paper, he treats Zamia wallisii as the sister species of Zamia dressleri, rather than Zamia skinneri, despite similar leaflets, because of the cones and the habit; he sees the two as local relics of a once more widespread ancestral species. That passage, incidentally, reverses the distinguishing character by mistake, attributing the grooved stalklet to Zamia dressleri (Stevenson, 1993).

Molecular data tell a different story. In the transcriptome study of Lindstrom and colleagues (2024), which included a sample from Colón, Zamia dressleri falls in clade V, the Isthmus clade, where it is placed with the epiphytic Zamia pseudoparasitica within the Obliqua subclade; the authors call this placement “peculiar”, so extreme are the differences in form and habitat between a small terrestrial plant with one or two pleated leaves and the only epiphytic cycad. They add that Calonje and colleagues (2019) had also placed the two species in the Obliqua subclade, in separate branches. Zamia wallisii, for its part, belongs in the same study to clade VI, the West Andes clade, with Zamia oligodonta and Zamia montana. The molecular results therefore do not support Stevenson’s suggestion of a close relationship between Zamia dressleri and Zamia wallisii; the resemblance of their leaflets would then be a convergence, which the sources do not discuss.

Etymology and history

The species is named after Robert Louis Dressler (1927-2019), a botanist of the Missouri Botanical Garden who helped with the study of the cycads of Panama and was the first to recognise it as a distinct species (Stevenson, 1993; Haynes, 2022). Stevenson also thanks him for his work on the genus in Panama, without which the revision could not have been completed. Before 1993 the species had been collected in Colón province (J. Cowell, R. Dressler, S. Kiem and K. Norstog) and in Kuna territory (H. Herrera, G. de Nevers).

According to Vannini (2019), mature plants were widely extracted and exported by foreign collectors in the 1990s and 2000s; almost all of them, he thinks, have probably died in cultivation.

Common names

No vernacular name is attested, and there is no English name: the plant is known by its scientific name.

In the wild

The World List of Cycads records the species in Colón province and the comarca of Guna Yala, in eastern Panama. The type was collected at 300 m. In 1993 Stevenson knew it from only two small, separate populations; he described neither the forest type nor the soil, and did not publish localities, for fear of collecting (Stevenson, 1993).

Vannini (2019) gives a fuller picture from the field: Zamia dressleri grows in central Panama on the Caribbean slope and just over the Continental Divide, on heavy soils in low to very low elevation tropical rainforest. Anecdotal reports, he writes, indicate that it was once locally abundant at a couple of easily accessible localities near the coast; because of collecting and habitat transformation, it is now usually found as discrete pockets of immature or young mature plants. He cites it among the Panamanian species whose once robust populations have been decimated by development. Its pollinator is not documented.

Conservation status and regulation

Zamia dressleri is rated Endangered (EN) on the IUCN Red List, in the assessment by J.D. Bösenberg published in 2022, under criteria B1ab(iii,v): a small range, with a decline in habitat quality and in the number of mature individuals (The World List of Cycads; GBIF gives the same category; the Red List itself could not be consulted). The decline of the wild populations described by Vannini (2019), through the export of mature plants and the loss of habitat, matches these criteria.

Like all Zamia except Zamia restrepoi, Zamia dressleri falls under CITES Appendix II, where the genus has been listed since 4 February 1977. International trade in the plants is allowed but requires an export permit issued by the country of origin. The listing carries annotation #4: seeds, pollen, seedlings and tissue cultures obtained in vitro and transported in sterile containers are not covered by CITES. In the European Union the species falls under Annex B of Regulation (EC) No 338/97, whose current list is set by Regulation (EU) 2026/1383, applicable since 29 June 2026.

This general information does not replace the official texts: check the regulations in force before buying or exchanging plants, ask the seller for proof of origin and prefer plants raised from seed in cultivation; plants from artificial propagation now exist, as Vannini’s Californian seedling shows.

Growing Zamia dressleri

The species is rare and difficult in cultivation, and every source that discusses it agrees on that. Vannini (2019) writes that, although highly prized for its striking mature leaves, it is not an easy plant for most people, and that many experienced cycad growers have found it challenging as a pot plant. His own experience is that it needs excellent drainage and year-round warmth, even overnight; it grows slowly from seed to maturity, and drenches of chelated iron every few months seem to improve its colour and vigour. He counts it, with Zamia manicata and Zamia hamannii, among the lowland rainforest species that need uniformly warm temperatures day and night, and reports inconclusive trials of mycorrhizal fungi and bacterial inoculants on it.

Jungle Music, in San Diego, recommends filtered light and good drainage in the garden, and counts it among the Zamia, with Zamia skinneri and Zamia cremnophila, that “require very tropical conditions”. Simon Lavaud, of the French specialist nursery Cycadales.eu, places it in his group of the Zamia of Costa Rica, Panama and the lowland forests of South America, rated “difficult” outside the tropics (Lavaud, 2023). For this group he recommends:

  • a free-draining compost and water that are neutral to acid;
  • night temperatures around 22 °C (71.6 °F), with only brief spells at about 15 °C (59 °F) tolerated;
  • day temperatures of 28 to 30 °C (82.4 to 86 °F); most species tolerate 34 to 35 °C (93.2 to 95 °F), but heat peaks can damage new leaves;
  • high air humidity, between 70 and 90 per cent;
  • in Europe, a glasshouse, conservatory, bright heated room or growth chamber.

Outdoor and in-ground cultivation

No in-ground growing result has been published outside the tropics. The advice of Jungle Music for the garden (filtered light, good drainage) concerns frost-free climates; Vannini (2019) notes that some Mesoamerican cycads have been trialled outdoors in southern Florida and coastal southern California, but he does not say that Zamia dressleri is one of them.

Container cultivation

Most growers keep it in a pot under glass. For Central American and Panamanian cycads in pots, Vannini (2019) recommends light to medium shade and a very free-draining mix with at least 50 per cent pumice (preferred) or medium-grade perlite, the rest being fine conifer bark and well-composted forest products in equal amounts; he warns that mineralised tap water can leave halos on leaflets and burn the roots and leaf tips of some delicate Zamia, so that growers may want to try reverse-osmosis or distilled water for species that are not thriving. In cool climates this means a heated glasshouse with constant warmth, shade and humidity.

In cultivation in the UK, US and Australia

In short: present in several American collections; no British or Australian record.

  • United States: Montgomery Botanical Center (Coral Gables, Florida) lists two accession numbers in its online catalogue (2000332 and 20140733, the second from 2014). Montgomery, Marie Selby Botanical Gardens (Sarasota, Florida), the Huntington (San Marino, California), San Diego Botanic Garden (Encinitas, California), the Atlanta Botanical Garden (Georgia) and the New York Botanical Garden declare it to BGCI (queried on 25 October 2026). Vannini (2019) grows it in his collections in the United States (California) and Guatemala, including a year-old seedling from artificial propagation.
  • United Kingdom: no record in BGCI or in the online catalogues of British gardens (Edinburgh, Cambridge, Chelsea Physic Garden).
  • Australia: no record in BGCI or in the online catalogues of Australian gardens.

Outside these countries, BGCI also lists the Prague Botanical Garden. A BGCI declaration shows that a garden held the plant at some point, not that it is alive today, and the sources do not say whether these plants are grown outdoors or under glass.

Propagation

Like all Zamia, the species has separate male and female plants and is propagated from seed; seedlings from artificial propagation are now grown in the United States (Vannini, 2019). No germination data specific to the species have been published. Growth from seed to maturity is slow. Seeds are exempt from CITES under annotation #4, but they must come from plants of legal origin.

Pests and diseases

No pest or disease specific to the species has been documented. The failures reported in cultivation are attributed to growing conditions (cold nights, poor drainage, low humidity) rather than to an identified parasite. For Central American Zamia in general, Vannini (2019) recommends fungicide drenches and sprays when prolonged wet weather is expected, to prevent caudex rot and leaf spotting.

Cold hardiness

No measured data on cold tolerance exist for Zamia dressleri. It is a species of humid tropical lowlands, and growers stress that it needs warmth day and night all year; Jungle Music warns that such species do not tolerate cold weather well and may actually die from cold.

Mediterranean and European experience

No in-ground growing has been reported in France, and no dated frost episode concerns the species. French growers keep it under glass: one grower on the Côte Bleue, west of Marseille, wrote on the Fous de palmiers forum in July 2012 that only two plants were left of those he had grown, “in poor shape despite fairly advanced conditions”, and judged the balance between compost moisture, air humidity, heat and light very hard to find. Another grower showed young plants raised under glass in May 2013. This Mediterranean experience, a failure under glass rather than a cold record, is useful to growers in comparable climates such as California or southern Australia: even there, the plant belongs in a heated, humid glasshouse.

United Kingdom, United States and Australia

No dated cold record has been published. Trebrown, a British specialist nursery, gives the species a cold hardiness zone of 10b in its catalogue, without stating the basis of this commercial rating; it should not be taken as a measured limit, and the growers’ accounts above suggest that cool nights well above freezing are already a problem.

Toxicity and precautions

No toxicity study specific to Zamia dressleri has been published. The risk is, however, documented in the genus and in other cycads: Zamia contain toxic glycosides (cycasin, macrozamin), from which methylazoxymethanol is derived, and for Zamia furfuracea the ASPCA cites cycasin and BMAA, a neurotoxic amino acid, with vomiting, bloody diarrhoea and liver damage in dogs, cats and horses; the seeds are the most dangerous part. In the absence of evidence to the contrary, treat the plant as poisonous: keep seeds and leaves out of reach of children and animals, and wear gloves to clean seeds. If any part is swallowed, contact a poison centre, a doctor or a vet straight away.

Traditional uses

No use has been documented.

Frequently asked questions

Where does Zamia dressleri grow?

Only in Panama, in Colón province and the comarca of Guna Yala, on the Caribbean slope and just over the Continental Divide, in lowland rainforest; the type was collected at 300 m.

Why is it called “dressleri”?

In honour of Robert L. Dressler (1927-2019), a botanist of the Missouri Botanical Garden, who was the first to recognise it as a distinct species.

Does it resemble Zamia amplifolia?

Yes: both have huge grooved leaflets and few leaves. Zamia amplifolia grows in Colombia, Zamia dressleri in Panama, and molecular data have not yet shown how closely they are related.

How big does it get?

It stays low, but its leaflets are very large. Its stem is underground; the original description gives one leaf 0.5 to 1.5 m long with leaflets 30 to 50 cm by 12 to 15 cm, and old plants in the wild can carry up to three leaves about 1.85 m long.

Is it endangered?

Yes. The IUCN has rated it Endangered since 2022; collecting of mature plants and habitat loss have reduced its wild populations.

Is it easy to grow?

No. Experienced growers in the United States and France describe it as challenging: it needs warmth day and night all year, excellent drainage, shade and high humidity.

How much cold can it take?

Very little, as far as growers can tell, but no measured data exist. In the UK it needs a heated glasshouse that stays warm at night.

Further reading on Succulentes

Sources

Reference sites

Bibliography

  • Stevenson, D.W. (1993). The Zamiaceae in Panama with comments on phytogeography and species relationships. Brittonia 45(1): 1–16. https://doi.org/10.2307/2806850 [Revision of the Panamanian Zamia and protologues of Zamia cunaria, Zamia dressleri, Zamia ipetiensis and Zamia neurophyllidia; full text read: description, type, affinities, distribution.]
  • Lindstrom, A., Habib, S., Dong, S., Gong, Y., Liu, J., Calonje, M., Stevenson, D. & Zhang, S. (2024). Transcriptome sequencing data provide a solid base to understand the phylogenetic relationships, biogeography and reticulated evolution of the genus Zamia L. (Cycadales: Zamiaceae). Annals of Botany 134(5): 747–768. https://doi.org/10.1093/aob/mcae065 [Sample from Colón; position in clade V (Obliqua subclade) next to Zamia pseudoparasitica; full text consulted.]
  • Calonje, M., Meerow, A.W., Griffith, M.P., Salas-Leiva, D., Vovides, A.P., Coiro, M. & Francisco-Ortega, J. (2019). A time-calibrated species tree phylogeny of the New World cycad genus Zamia L. (Zamiaceae, Cycadales). International Journal of Plant Sciences 180(4): 286–314. [Obliqua subclade; not consulted, cited after Lindstrom and colleagues (2024).]
  • Stevenson, D.W. (2001). Zamiaceae. In: Flora de Colombia 21. Instituto de Ciencias Naturales, Universidad Nacional de Colombia, Bogotá. [Commentary on Zamia amplifolia citing Norstog and Nicholls (1997); online version read.]
  • Lavaud, S. (2023). Comment cultiver les Zamia en climat tempéré. Cycadales.eu. [Growing advice for groups of species; read directly.]
  • Vannini, J. (2019). Central American and Panamanian cycads in field and greenhouse. Exotica Esoterica, 17 February 2019. [Online article by a naturalist and collector; read.]
  • Bösenberg, J.D. (2022). Zamia dressleri. The IUCN Red List of Threatened Species 2022: e.T42133A69837368. [Current assessment (EN); reference taken from The World List of Cycads, Red List page not consulted.]
  • 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; not consulted directly.]
  • 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; consulted directly.]