Zamia stevensonii

Zamia stevensonii is a small cycad with an above-ground stem from central Panama, known from the area around the Panama Canal, in the province of Panamá, where it grows in lowland tropical forest. Described in 2012 by A. S. Taylor Blake and Greg Holzman after sixteen years of study, this species of the genus Zamia had previously been confused with other trunk-forming Panamanian zamias, especially Zamia elegantissima, to which it is closely related. Before it was named, it circulated among collectors as Zamia sp. “blanco”, after its white new leaves. The IUCN rates it Endangered.

Key facts about Zamia stevensonii

  • Accepted name: Zamia stevensonii A.S.Taylor & Holzman (2012), accepted by The World List of Cycads (version 2026.08.15) and by GBIF; POWO could not be consulted directly
  • Former names and synonyms: no synonyms; trade name Zamia sp. “blanco” (also “El Blanco”)
  • Family: Zamiaceae, order Cycadales
  • Common names: no English name and no known local name; “blanco”, a cycad-trade name referring to the white new leaves
  • Natural range: Panama, province of Panamá (Canal area, including Chagres National Park); lowland tropical rainforest, from 110 m to over 700 m
  • IUCN status: Endangered (EN), criteria B1ab(iii,v)+2ab(iii,v), assessment published in 2022 (the authors of the description had proposed Critically Endangered in 2012)
  • 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 figures; a strictly tropical plant according to growers (see Cold hardiness)
  • Light and soil: in the wild, the understorey of secondary forest, on basic, humus-covered forest soils; in cultivation, warmth and high humidity (Cycadales.eu)
  • Habit and adult size: solitary stem up to 1.5 m tall and 2 to 8 cm across, often almost absent; on average 11 leaves (up to 27), 25 to 120 cm long, emerging white
  • In the UK, US and Australia: Montgomery Botanical Center (Florida), Longwood Gardens (Pennsylvania) and two Hawaiian gardens (US, BGCI and catalogue); 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 stevensonii

The new leaves are the giveaway: they almost always emerge white and hairless before turning glossy to dark green. Zamia stevensonii is one of the four terrestrial zamias of Panama whose stem grows above ground, and the smallest of them; it looks most like Zamia elegantissima. The measurements below come from the original description, based on more than 500 plants observed in the field (Taylor Blake and Holzman, 2012).

  • Stem: solitary, up to 1.5 m tall (rarely over 1 m) and 2 to 8 cm across; many coning plants have almost no above-ground stem. The plant recovers quickly from injury.
  • Leaves: up to 27 per crown (11 on average), 25 to 120 cm long, with 3 to 25 pairs of leaflets (11.5 on average). The mid-green petiole is 28 to 63 cm long and carries very few prickles, or none. In shade, new leaves may emerge yellowish white before turning snow white.
  • Leaflets: oblong, slightly sickle-shaped towards the base, acuminate, with a flat surface, lacking the lengthwise fold of Zamia pseudomonticola and Zamia fairchildiana; the margin is finely toothed, mainly in the upper third or quarter. Apical leaflets 7 to 24 cm by 2 to 5 cm, median leaflets 10 to 25 cm by 2 to 5 cm, basal leaflets 9 to 21 cm by 1.5 to 4 cm.
  • Male cones: one to three, cylindrical to elongate-conical, 5.5 to 17 cm long and 2.5 to 4 cm across, covered in reddish-gold to brownish-yellow felt; peduncle 4 to 10 cm long. The microsporophylls form 13 to 16 columns and 20 to 38 rows; pollen sacs occur only on their lower face, whereas Zamia pseudomonticola and Zamia fairchildiana carry them on both faces.
  • Female cones: solitary, rarely two, cylindrical to cylindrical-globose, 4.5 to 16 cm long and 4 to 9 cm across in the description (up to 20 cm long according to the discussion in the same paper); brownish-yellow felt when young, later green or greyish green with tawny to brown felt; peduncle up to 10 cm, almost always covered in bracts. The megasporophylls form 3 to 7 columns and 3 to 9 rows.
  • Seeds: ovoid to globose, 1.8 to 2.1 cm long and 1.2 to 1.5 cm across, with a bright red sarcotesta when ripe; from 24 to more than 126 per cone according to the English description (more than 144 according to the Latin diagnosis).
  • Seedlings: the first leaves usually carry four oval, pointed leaflets, white or nearly so when they emerge.

Hybrids

No hybrid involving Zamia stevensonii, natural or artificial, has been published.

Possible confusion

The four Panamanian zamias with an above-ground stem have often been confused or poorly delimited, but their ranges are separate, which helps with identification (Taylor Blake and Holzman, 2012):

  • Zamia pseudomonticola: north-western Chiriquí province, above 1,000 m;
  • Zamia fairchildiana: a small forest area in south-western Chiriquí;
  • Zamia elegantissima: north of the Canal, in Colón province, and further east into part of the Guna territory (Kuna Yala); the most similar species;
  • Zamia stevensonii: near the Canal, in Panamá province.

According to the authors, the two western species resemble each other more, as do the two eastern ones; vegetative and reproductive differences nevertheless separate all four clearly. Against Zamia elegantissima, their key uses two simple characters: white new leaves and a stem base less than 8 cm across in Zamia stevensonii; light green to yellowish-green new leaves and a stem base more than 8 cm across (up to 21 cm) in Zamia elegantissima. Zamia stevensonii also has fewer leaves and leaflets, smaller cones and seeds, and seedlings usually with four leaflets, against six in Zamia elegantissima.

Taxonomy

Zamia stevensonii is an accepted name with no synonyms, according to The World List of Cycads and GBIF; POWO could not be consulted directly. It was described in 2012 by A. S. Taylor Blake and Greg Holzman in The Botanical Review (volume 78, pages 335 to 344), in a paper titled “A new Zamia species from the Panama Canal area”.

The authors explain that after sixteen years of research on the plant they decided to describe it as new, stressing its resemblance to Zamia elegantissima and its differences from Zamia pseudomonticola and Zamia fairchildiana. They also note differences in pollinators between these species, all weevils of the genus Rhopalotria and beetles of the genus Pharaxonotha. According to them, the plant had earlier been referred to Zamia fairchildiana, then to Zamia elegantissima. The description rests on field measurements taken over more than twenty years on more than 500 plants at the two known sites (Taylor Blake and Holzman, 2012; the summary speaks of sixteen years of research).

The transcriptome-based phylogeny of Lindstrom and colleagues (2024), which included a plant from Panamá province, confirms this relationship: Zamia stevensonii forms a small group with Zamia elegantissima and Zamia obliqua, sister to the group of Zamia dressleri and the epiphytic Zamia pseudoparasitica, within the “Isthmus” clade, the most morphologically diverse of the genus.

Etymology and history

The epithet stevensonii honours Dennis William Stevenson of the New York Botanical Garden. The authors recall his systematic work on the cycads of Panama and the American tropics, and that he was the first to publish a usable key to the Panamanian cycads (Taylor Blake and Holzman, 2012; see also Haynes, 2022).

The type (A. S. Taylor CCh23052012) was collected on 23 May 2012 by A. S. Taylor Blake and Greg Holzman in Panamá province, at about 110 m, on loose black soil covered in leaf litter near a freshwater lake, in herbaceous and mostly shrubby vegetation with a few trees. The holotype is kept at the herbarium of the University of Panama (PMA), with isotypes in New York (NY) and Xalapa (XAL) (Taylor Blake and Holzman, 2012).

Before it was described, the plant circulated among enthusiasts as Zamia sp. “blanco”, a name the authors explain by the colour of its new leaves; the French nursery Cycadales.eu notes that its seeds were sold as Zamia sp. “El Blanco”. In 2013 a member of the French forum Fous de palmiers announced an order of seed of “Zamia stevensonii (sp. blanco)”, and a grower in Ravenna (Italy) showed the new leaves of a plant on the Italian forum Tropicamente under the name “Zamia stevensonii (blanco)”.

Common names

There is no English name, and the authors state that the species has no known local name in Panama. “Blanco” (“white” in Spanish) is the name under which it is widely known in the cycad trade, from the white colour of the new leaves (Taylor Blake and Holzman, 2012). Growers were still using it in 2013.

In the wild

Zamia stevensonii is endemic to the Panama Canal area, in Panamá province; it occurs notably near the headwaters of the río Chagres, in Chagres National Park. It grows in lowland tropical rainforest, mainly secondary forest, near lakes and rivers, from 110 m to over 700 m, on basic, humus-covered forest soils, loose or compact. The climate is tropical, with a rainy season that usually lasts from early April to late December. The authors know two sites, divided into five fragmented sub-sites (Taylor Blake and Holzman, 2012).

Reproduction: male plants reach maturity in about four years, females in about eight. Cones form from late July to early September, depending on the strength of the rainy season; pollen is shed and female cones are receptive from mid-November to early December, once a year. Seeds take about one to two years to ripen, and seeds without an embryo sometimes form for lack of pollen.

Pollination: exclusion trials against wind and insects showed that pollination is carried out by insects, an as yet undescribed beetle of the genus Pharaxonotha (Erotylidae), present in all populations and regarded as the main pollinator, and, in most populations, a weevil close to the genus Rhopalotria.

Populations: the species is abundant only near the Canal, and its total numbers are unknown. The best-preserved site lies in a national park that once housed a United States Army post, handed back to Panama after the Torrijos–Carter treaties. The authors report illegal collecting for sale and poor recruitment of young plants (Taylor Blake and Holzman, 2012).

Conservation status and regulation

Zamia stevensonii is rated Endangered (EN) on the IUCN Red List under criteria B1ab(iii,v)+2ab(iii,v), which reflect a very small range with a decline in habitat quality and in the number of mature individuals (assessment by A. Taylor-Blake published in 2022, according to The World List of Cycads; category confirmed by GBIF; the Red List page could not be consulted). In the original description the authors proposed Critically Endangered (CR B1B2ab(ii,v)), because of habitat destruction within a small range; the 2022 assessment settled on Endangered.

Like all Zamia except Zamia restrepoi, which is in Appendix I, Zamia stevensonii falls under CITES Appendix II, where the genus has been listed since 4 February 1977. The listing carries annotation #4 (version adopted at CoP20, in force on 5 March 2026): seeds, pollen, seedlings and tissue cultures obtained in vitro and transported in sterile containers, and cut flowers of artificially propagated plants, are not covered by CITES. International trade in the plants themselves, on the other hand, requires an export permit. In the European Union the species is listed in Annex B of Regulation (EC) No 338/97, whose annexes are now set by Regulation (EU) 2026/1383, applicable since 29 June 2026. Species+ lists the species by name under the genus listing (checked on 3 October 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 cultivated seed.

Growing Zamia stevensonii

Growers agree that Zamia stevensonii needs constant warmth and humidity. The French specialist nursery Cycadales.eu, which sells seedlings, describes it as purely tropical: it dislikes temperatures below 20 °C (68 °F) and above 32 °C (90 °F), and humidity should ideally be 70 to 90 % (product page, read on 25 October 2026). In his growing guide, Simon Lavaud of the same nursery places it in his “difficult” group of zamias from the lowland forests of Central and South America, which generally suffer from a lack of heat in Europe even in summer. For this group he advises a free-draining, neutral to acid compost and water, nights at about 22 °C (72 °F) with brief drops to about 15 °C (59 °F) tolerated, days at 28 to 30 °C (82 to 86 °F), and 70 to 90 % humidity; most species tolerate 34 to 35 °C (93 to 95 °F), but heat peaks can damage new leaves, and he singles out Zamia stevensonii as rather sensitive to this. He recommends a glasshouse, conservatory, bright heated room or indoor growing chamber (Lavaud, 2023).

In Panama, the authors of the description note that the species is often seen in gardens and is sold by local nurseries. In the wild they describe it as very robust: it withstands drought and regrows even from small stem fragments (Taylor Blake and Holzman, 2012). These field observations are not growing instructions.

Outdoor and in-ground cultivation

Outdoor cultivation is documented only in the tropics: in Panamanian gardens (Taylor Blake and Holzman, 2012) and at Montgomery Botanical Center in Coral Gables, Florida, whose cycad collection is grown outdoors. Elsewhere, its narrow comfort range makes outdoor planting unrealistic.

Container cultivation

Its small size makes it a good candidate for a pot in a heated glasshouse or a warm, bright room, provided the humidity is high. No detailed container-growing report has been published; the 2013 Italian plant was shown without any information on how it was grown.

In cultivation in the UK, US and Australia

In short: well represented at Montgomery Botanical Center, otherwise rare in collections, and absent from British and Australian records.

  • United States: the online catalogue of Montgomery Botanical Center (Coral Gables, Florida) lists twenty accession numbers, the earliest from 1999 (99885 to 99890) and the most recent from 2003 (20030361). BGCI also records it at Longwood Gardens (Kennett Square, Pennsylvania), the National Tropical Botanical Garden (Kalāheo, Hawaii) and the botanical garden of the University of Hawaii at Hilo (catalogue and BGCI queried on 25 October 2026).
  • Australia: no record in BGCI or in the online catalogues of Australian gardens.
  • United Kingdom: no record in BGCI or in the online catalogues of British gardens.

A BGCI declaration shows that a garden held the plant at some point, not that it is alive there today. Elsewhere, BGCI records it at the Hortus Botanicus in Amsterdam.

Propagation

Like all Zamia, the species has separate male and female plants and is propagated from seed; seed has been sold in the specialist trade (Fous de palmiers forum, 2013), and seedlings are offered by Cycadales.eu. In the wild, seeds take one to two years to ripen, and injured or cut stems regrow, even from small fragments (Taylor Blake and Holzman, 2012); no trial of propagation from stem pieces in cultivation has been published. Seeds are exempt from CITES under annotation #4, but should be of legal origin.

Pests and diseases

In the wild, caterpillars of the butterfly Eumaeus godarti (Lycaenidae) eat young and old leaves and also damage female cones; they consume a lot of foliage without serious harm to the population, and the smallest seem to be hunted by birds. A leaf beetle of the genus Alacoscelis attacks the young leaves (Taylor Blake and Holzman, 2012). No pest or disease specific to the species has been documented in cultivation, where Zamia are mainly at risk from rot in cold, sodden compost, and from scale insects.

Cold hardiness

There are no measured figures for the cold tolerance of Zamia stevensonii, and it should be treated as one of the least hardy zamias. It lives at low altitude in central Panama, under a tropical climate, and growers place its comfort threshold well above freezing: Cycadales.eu says it dislikes temperatures below 20 °C (68 °F).

Mediterranean and European experience

No cultivation result has been published in France in the ground or in pots: the French forum Fous de palmiers mentions it only in connection with a seed order (2013). In Italy, a grower in Ravenna showed the new leaves of a plant on the Tropicamente forum in June 2013, without saying whether it was in a pot, under glass or outdoors, or what temperatures it had experienced. No dated frost episode concerns this species, and the Jardin zoologique tropical in La Londe-les-Maures (Var, on the French Riviera) has published no observation of it. Even in Mediterranean-type climates such as California or southern Australia, it belongs under glass.

United Kingdom, United States and Australia

No cold record and no USDA rating have been published. Outdoor cultivation is realistic only in frost-free tropical areas such as southern Florida or Hawaii, where it is grown at Montgomery and in two Hawaiian gardens; in the UK it needs a heated glasshouse kept above about 15 °C (59 °F) at night, following the group advice above.

Toxicity and precautions

No toxicity study specific to Zamia stevensonii has been published. The risk is, however, well documented in cycads: Zamia contain toxic glycosides (cycasin, macrozamin), from which methylazoxymethanol is derived, harmful to the liver and nervous system, and cycads also contain a neurotoxic amino acid, BMAA; the seeds are the most dangerous part. Within the genus, the ASPCA lists Zamia furfuracea as toxic to dogs, cats and horses. 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 is documented for this species.

Frequently asked questions

Who is Stevenson?

Dennis William Stevenson, a botanist at the New York Botanical Garden and a cycad specialist. The species was named after him for his many contributions to cycad research.

What is Zamia “blanco”?

The same plant. “Blanco” is the name under which it circulated among collectors before it was described in 2012 as Zamia stevensonii; it comes from the new leaves, which emerge white.

How can I tell it from Zamia elegantissima?

By the new leaves and the stem. Those of Zamia stevensonii emerge white and its stem is less than 8 cm across at the base; those of Zamia elegantissima emerge light green to yellowish green, on a thicker stem (up to 21 cm). The two also live in different areas: near the Canal for the first, north of the Canal (Colón) and further east for the second.

How big does it get?

It stays small. The stem rarely exceeds 1 m (1.5 m at most) and is 2 to 8 cm across, and the leaves are 25 to 120 cm long; many adult plants have almost no above-ground stem.

Is it endangered?

Yes. The IUCN rates it Endangered because of its very small range and the decline of its habitat and populations; in 2012 the authors of the description even proposed Critically Endangered, reporting illegal collecting.

Is it hardy?

No. There are no cold data, but it comes from the tropical lowlands and growers advise keeping it above about 20 °C (68 °F); outside the tropics it needs a heated glasshouse or a warm room.

Is it poisonous?

It must be assumed so. No analysis concerns the species, but the cycads studied contain serious toxins, especially in the seeds.

Further reading on Succulentes

Sources

Reference sites

Bibliography

  • Taylor Blake, A.S. & Holzman, G. (2012). A new Zamia species from the Panama Canal area. The Botanical Review 78(4): 335–344. https://doi.org/10.1007/s12229-012-9105-4 [Original description; full text read in the copy published by The Cycad Society.]
  • 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 [Full text read on PubMed Central.]
  • Taylor-Blake, A. (2022). Zamia stevensonii. The IUCN Red List of Threatened Species 2022: e.T66911767A66911778. https://doi.org/10.2305/IUCN.UK.2022-1.RLTS.T66911767A66911778.en [IUCN assessment; reference checked on Crossref, category confirmed by GBIF; the Red List page could not be consulted.]
  • Lavaud, S. (2023). Comment cultiver les Zamia en climat tempéré. Cycadales.eu. [Growing advice for groups of species; read directly.]
  • 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.]