Cycas dolichophylla

Cycas dolichophylla is a cycad of northern Vietnam and the far south of China, where it grows in the shade of evergreen forest in the Red River region. This member of the genus Cycas is recognised above all by its leaves, among the longest in the genus at 2 to 4.5 m, carried on a stout trunk that rarely exceeds 1.5 m. It was only described in 2004, by the Australian botanist Ken Hill and his Vietnamese colleagues, yet according to Hill it is the most widespread and abundant cycad of northern Vietnam. It has no former scientific name: before 2004 these plants were simply not told apart. The IUCN lists it as Near Threatened and, like every Cycas but one, it is in CITES Appendix II.

Key facts about Cycas dolichophylla

  • Accepted name: Cycas dolichophylla K.D.Hill, T.H.Nguyên & P.K.Lôc (2004), accepted by The World List of Cycads (version 2026.08.15); the World Checklist of Vascular Plants (WCVP), on which POWO is based, also accepts it (consulted through GBIF on 31 October 2026)
  • Former names and synonyms: none listed by The World List of Cycads
  • Family: Cycadaceae, order Cycadales; section Stangerioides (Hill 2008)
  • Common names: no English name could be traced to a reliable source (see Common names)
  • Natural range: northern Vietnam (eleven provinces) and China (Guangxi, Yunnan); presence in Laos uncertain
  • IUCN status: Near Threatened (NT), confirmed by the reassessment by J. D. Bösenberg published in 2023, which replaced that of H. T. Nguyen (2010, NT A4cd)
  • CITES and other protection: CITES Appendix II; Annex B in the European Union
  • Documented hardiness: no measured value and no dated growing report (see Cold hardiness)
  • Light and soil: in the wild, deep shade in closed forest, on loamy soils over limestone, schist or granite; needs in cultivation not documented
  • Habit and adult size: trunk up to 1.5 m tall and 18 to 30 cm across; 8 to 40 leaves 2 to 4.5 m long
  • In the UK, US and Australia: Royal Botanic Garden Sydney (accession of 2021); listed by Cairns Botanic Gardens and Atlanta Botanical Garden in BGCI PlantSearch; no British record (see In cultivation in the UK, US and Australia)
  • Toxicity: not studied for the species; treat it as poisonous, like all Cycas (see Toxicity and precautions)

How to recognise Cycas dolichophylla

The combination of a short, stout trunk and huge, very glossy leaves with broad leaflets rounded at the base identifies it. The description below is Ken Hill’s, from his revision of the Cycas of China (2008), which follows the original description of 2004.

  • Trunk: above ground, up to 1.5 m tall and 18 to 30 cm in diameter at the narrowest point.
  • Crown: 8 to 40 bright to deep green, very glossy leaves.
  • Leaves: 2 to 4.5 m long, flat in section, with 150 to 270 leaflets; young leaves carry an orange down that is shed as they open; the rachis always ends in a pair of leaflets.
  • Petiole: 40 to 110 cm, that is 20 to 35 % of the leaf, smooth, armed with spines 4 to 10 mm long along almost its whole length.
  • Median leaflets: 19 to 42 cm long and 14 to 25 mm wide, clearly rounded at the base, 16 to 30 mm apart, with wavy margins and a soft tip.
  • Male cones: narrowly ovoid or spindle-shaped, yellow, 35 to 58 cm long and 8 to 10 cm across.
  • Megasporophylls: 15 to 26 cm, with brown down, bearing 2 to 4 ovules; the blade is rounded and deeply cut into 16 to 26 soft spines 4 to 5 cm long.
  • Seeds: ovoid, 4 to 6.4 cm long, with a yellow fleshy coat (sarcotesta) and no inner spongy layer.

Hill sums up its distinguishing features as a robust but short aerial trunk, leaves longer and more numerous than in its relatives, numerous short, broad leaflets rounded at the base, long fine petiole spines, and large male cones whose scales lack an apical spine.

Hybrids

Hybrid forms are reported in the wild, although none has an accepted name. Hill (2008) describes village-grown plants around Vo Nhai and Yen Son, in Thai Nguyen Province, Vietnam, that are intermediate between Cycas dolichophylla and Cycas ferruginea, which he interprets as hybrids: the latter grows on limestone cliffs, the former in the neighbouring forests on deep soils. He also reports intermediate forms with Cycas bifida west of Thai Nguyen, and a transition zone with Cycas collina west of Moc Chau, in Son La Province.

Cycas multifrondis, described in 1996 from a plant grown at Xiamen Botanical Garden, was in Hill’s view (2008) one form of a hybrid swarm between Cycas dolichophylla and Cycas bifida; The World List of Cycads now accepts it as a species. A Chinese genomic study (Tao et al. 2021) of six species from southern China found strong genetic admixture in the five individuals of Cycas dolichophylla analysed: about 45 % of their genome shared with Cycas bifida, 34 % with Cycas balansae and 21 % with Cycas changjiangensis, together with signs of gene flow with Cycas szechuanensis. The authors themselves stress how small this sample is.

Possible confusion

In cultivation, the commonest mix-up is with Cycas siamensis. In 2010, on the French forum Fous de palmiers, several growers compared plants bought in Europe as Cycas dolichophylla; a member who had seen the species in Vietnam identified them as Cycas siamensis, which has much shorter leaves and narrow leaflets. Before buying, check the width of the leaflets and the length of the adult leaves.

In the wild, several related species of northern Vietnam and Yunnan can cause confusion:

  • Cycas balansae: Hill’s key (2008) separates it by its leaflets, narrowed and tapering at the base, and its longer petiole (30 to 40 % of the leaf, against 20 to 35 %); the megasporophylls are similar but larger and sturdier in Cycas dolichophylla.
  • Cycas tanqingii: longer, more widely spaced leaflets that are not rounded at the base, and a longer petiole (Hill 2008).
  • Cycas collina: no aerial trunk, and shorter petiole spines (1 to 3 mm), according to Hill’s key (2008).
  • Cycas ferruginea: a smaller species of limestone cliffs, with which Cycas dolichophylla hybridises locally.

Taxonomy

Cycas dolichophylla is a species accepted by The World List of Cycads; the World Checklist of Vascular Plants (WCVP), on which POWO is based, also accepts it (consulted through GBIF on 31 October 2026). Ken Hill, Nguyen Tien Hiep and Phan Ke Loc described it in 2004 in their revision of the Cycas of Vietnam, published in The Botanical Review (volume 70, pages 157–160, figure 7). The type was collected on 2 November 1996 by Nguyen Tien Hiep on Mount Pu La, in Na Hang District (Tuyen Quang Province, Vietnam), and is held at the Hanoi herbarium (HN).

The authors’ abbreviation varies between sources: “K.D.Hill, T.H.Nguyên & P.K.Lôc” in The World List of Cycads, “K.D.Hill, H.T.Nguyen & L.K.Phan” in Hill (2008) and in Species+. These are the same three authors; this page follows The World List of Cycads.

Hill (2008) places Cycas dolichophylla in section Stangerioides, the Cycas of China and Indochina with soft male cones and seeds lacking a fibrous layer. This separates it from Cycas pectinata, which Hill places in section Indosinenses, defined by stiff or woody male cones and a layer of fibrous tissue in the seed flesh. Within Stangerioides he recognises a possibly natural subgroup defined by a robust, erect aerial trunk, made up mostly of Chinese species (Cycas taiwaniana, Cycas diannanensis and Cycas hainanensis, the last now a synonym of Cycas taiwaniana for The World List of Cycads): Cycas dolichophylla is the only member of this group known outside China.

A phylogeographic study from the Kunming Institute of Botany (Zheng, Liu and Gong 2016), based on 13 populations covering almost the whole range, found two lineages separated by the Red River Fault, one to the south-west and one to the north-east, as well as a genetic split between Chinese and Vietnamese populations. These lineages are not treated as separate taxa.

Etymology and history

The epithet dolichophylla comes from the Greek dolichos, “long”, and phyllon, “leaf”, after the remarkably long leaves (Haynes 2022, cited by The World List of Cycads; Hill 2008 gives the same explanation).

According to Hill (2008), this cycad, the most widespread and abundant in northern Vietnam, was only recognised as a distinct species in the late 1990s. Most of the herbarium collections he cites date from 1996 to 2000, during surveys in Vietnam and Yunnan. No reliable information is documented on when it was introduced into cultivation in Europe, the United States or Australia; the accession of the Royal Botanic Garden Sydney dates from 2021.

Common names

No English common name could be traced to a reliable source. The Royal Botanic Garden Sydney labels it simply “Cycad”. No Vietnamese name specific to the species could be checked.

In the wild

Cycas dolichophylla grows in the evergreen forests of the Red River basin, from northern Vietnam to south-eastern Yunnan. The World List of Cycads records it in the Vietnamese provinces of Bac Kan, Cao Bang, Ha Giang, Hoa Binh, Lai Chau, Lao Cai, Ninh Binh, Son La, Thai Nguyen, Thanh Hoa and Tuyen Quang, in China in Guangxi and Yunnan, and doubtfully in Laos. Hill (2008) described a range from the Chinese border south to Ben En National Park, in Thanh Hoa Province, entering eastern Yunnan “very little”, with collections from Hekou and Pingbian counties.

It is locally common in sheltered sites, in the deep shade of tall, closed evergreen forest, on loamy soils over limestone, schist or granite; Hill notes that much of this forest is now reduced to scrubby regrowth and bamboo thickets. Two of the Vietnamese collections cited by Hill were made at about 400 m; the altitudinal range of the species is not documented. Zheng et al. (2016) describe a species adapted to warm, humid conditions, whose seeds, lacking a spongy layer, do not float, so that dispersal by water is limited. The same study and that of Tao et al. (2021) detect a sharp population contraction about 70,000 years ago, during the last glacial period.

The type comes from Vietnam, and no climatic data for its sites have been published.

Conservation status and regulation

Cycas dolichophylla is listed as Near Threatened (NT) by the IUCN. The reassessment by J. D. Bösenberg, published in Red List version 2023-1, replaced the assessment by H. T. Nguyen (2010), which The World List of Cycads gives as NT A4cd; the NT category is confirmed by the IUCN data relayed by GBIF (consulted on 21 October 2026). The GBIF data do not give the criteria of the 2023 assessment. Hill (2008) still gave the category Vulnerable, from Donaldson’s assessment (2003).

In China, Zheng et al. (2017) record the species in the provincial nature reserves of Gulinqing and Malipo (Yunnan) and note that, apart from Malipo, the populations observed are declining. Hill (2008) names the two main threats to Chinese cycads as habitat destruction and the collection of wild plants. A traveller on the Fous de palmiers forum reported in 2010 that in northern Vietnam he had seen the species only in village gardens, the forest habitat being heavily degraded.

Like the whole family Cycadaceae, it is listed in CITES Appendix II, with annotation #4 (CoP20 version, in force since 5 March 2026), which exempts seeds, pollen and seedlings or tissue cultures obtained in vitro in sterile containers; live plants still need permits. The United Kingdom, the United States and Australia apply CITES through their own national legislation; in the European Union the species is in Annex B of Regulation (EC) No 338/97, whose annexes in force are set by Commission Regulation (EU) 2026/1383, applicable since 29 June 2026. Species+ confirms this status and gives China and Vietnam as range states (consulted on 21 October 2026). This general information does not replace the official texts: check the rules in force before buying or exchanging plants, and ask for proof that a plant was raised in cultivation.

Growing Cycas dolichophylla

In short: no reliable growing data exist for this species. The points below are deductions from its habitat, to be taken as cautious guidelines rather than established rules.

Outdoor and in-ground cultivation

The species lives in deep shade in humid tropical to subtropical forest, which suggests filtered light rather than hot, full sun. It grows wild on loamy soils over various rocks, so a rich but free-draining soil should suit it, with no particular need for limestone. Its adult leaves, 2 to 4.5 m long, need a great deal of room. No outdoor growing result has been published anywhere, and its hardiness is unknown (see Cold hardiness): planting out can only be considered in frost-free, humid climates such as southern Florida, coastal Queensland or other tropical gardens, and even there it is untested.

Container cultivation

Only a young plant remains manageable in a pot; an adult crown of leaves several metres long soon outgrows any conservatory. In the United Kingdom and other temperate regions it is a plant for a heated glasshouse. No long-term report of container growing has been published.

In cultivation in the UK, US and Australia

In short: rare in public collections, and absent from British lists. A garden listed in the BGCI PlantSearch database (consulted in October 2026) has declared the species at some point, which does not prove that a living plant is there today.

  • Australia: the online catalogue of the Royal Botanic Garden Sydney (updated on 1 October 2026) lists one accession, S2021-0516, of garden provenance, under the name “Cycad”, with China as the native range. The Cairns Botanic Gardens list the species in BGCI PlantSearch.
  • United States: Atlanta Botanical Garden lists it in BGCI PlantSearch. It does not appear in the online catalogues of Montgomery Botanical Center or Fairchild Tropical Botanic Garden consulted in October 2026.
  • United Kingdom: no British garden lists the species in BGCI PlantSearch or in the online catalogues consulted.

No dated report from a private grower in the United Kingdom, the United States or Australia has been published.

Propagation

Like all Cycas, Cycas dolichophylla is dioecious: a male and a female plant are needed for fertile seed. It is propagated from fresh seed, as for other Cycas; no germination data specific to the species are published. A grower on the Fous de palmiers forum reported in December 2010 that seed brought back from Vietnam had germinated indoors, without further detail. Remove the fleshy seed coat wearing gloves before sowing, as it is toxic. Seeds are exempt from CITES under annotation #4; offsets are not documented for the species.

Pests and diseases

No data specific to Cycas dolichophylla are documented. The known risks for the genus apply: the Asian cycad scale, Aulacaspis yasumatsui, which can kill a plant, and root rot in poorly drained compost.

Cold hardiness

Its cold tolerance is unknown. No measured or reported value is documented in scientific publications, on the botanic garden and nursery websites consulted, or on the French and Italian growers’ forums. The only published indication is indirect: Zheng et al. (2016) describe a species adapted to warmth and humidity, whose populations retreated during the cold, dry phases of the Pleistocene.

The Jardin zoologique tropical at La Londe-les-Maures, in the south of France, has published no observation on the species. Until data appear, treat it as a frost-tender plant: frost-free under glass in the UK, and outdoors only in climates where frost is unknown.

Toxicity and precautions

No toxicity analysis specific to Cycas dolichophylla is documented, but the risk is well documented in the genus: Cycas tissues, and the seeds above all, contain cycasin, which is converted during digestion into methylazoxymethanol, toxic to the liver and nervous system, along with a neurotoxic amino acid, BMAA. In dogs, cats and horses the ASPCA reports vomiting, sometimes bloody diarrhoea, jaundice, liver damage and fatal cases, and Pet Poison Helpline adds neurological signs. Wear gloves to handle the seeds and their fleshy coat, pick up fallen seeds and keep plants out of reach of children and pets; if any part is swallowed, contact a poison centre, a doctor or a vet straight away.

Traditional uses

No traditional use specific to Cycas dolichophylla is documented. Hill (2008) only mentions many plants grown in villages and gardens in northern Vietnam, often brought in from nearby forest, without saying what they are used for.

Frequently asked questions

Is Cycas dolichophylla cold-hardy?

Nobody knows. No outdoor growing report and no measurement of cold tolerance has been published. Its humid tropical to subtropical forest habitat suggests growing it frost-free, under glass in the UK.

How long are its leaves?

From 2 to 4.5 m in adult plants, according to Hill (2008). With its leaflets 14 to 25 mm wide and rounded at the base, this is one of the best ways to tell it from other cycads of the region.

How does it differ from Cycas siamensis?

Clearly, in adult plants. Cycas siamensis has much shorter leaves and narrow leaflets; Cycas dolichophylla has huge leaves with broad leaflets. Plants sold in Europe as Cycas dolichophylla have turned out to be Cycas siamensis.

Is it endangered?

Not at present: the IUCN lists it as Near Threatened (2023). In China most observed populations are declining, and in Vietnam its forest habitat is heavily degraded.

Can it be grown in a pot?

Yes, while it is young. As an adult, its leaves several metres long make it hard to house, and no long-term container report has been published.

Does it hybridise with other cycads?

Yes, in the wild. Intermediate forms with Cycas ferruginea, Cycas bifida and Cycas collina are reported, and a genomic study shows extensive admixture with Cycas bifida, Cycas balansae and Cycas changjiangensis.

Is it poisonous?

It must be assumed so. There is no analysis for this species, but all parts of Cycas are poisonous, especially the seeds.

Further reading on Succulentes

Sources

Reference sites

Bibliography

  • Hill, K.D., Nguyen, H.T. & Loc, P.K. (2004). The genus Cycas (Cycadaceae) in Vietnam. The Botanical Review 70(2): 134–193. doi:10.1663/0006-8101(2004)070[0134:TGCCIV]2.0.CO;2 [Protologue, pages 157–160, figure 7; reference taken from The World List of Cycads and Crossref.]
  • Hill, K.D. (2008). The genus Cycas (Cycadaceae) in China. Telopea 12(1): 71–118. doi:10.7751/telopea20085804 [Full description, key, section Stangerioides, range, habitat, hybrids and intermediate forms, excluded names.]
  • Zheng, Y., Liu, J. & Gong, X. (2016). Tectonic and climatic impacts on the biota within the Red River Fault, evidence from phylogeography of Cycas dolichophylla (Cycadaceae). Scientific Reports 6: 33540. doi:10.1038/srep33540 [Phylogeography of 13 populations, two lineages, seed without spongy layer, demographic decline.]
  • Zheng, Y., Liu, J., Feng, X. & Gong, X. (2017). The distribution, diversity, and conservation status of Cycas in China. Ecology and Evolution 7(9): 3212–3224. doi:10.1002/ece3.2910 [Gulinqing and Malipo reserves, declining populations.]
  • Tao, Y., Chen, B., Kang, M., Liu, Y. & Wang, J. (2021). Genome-wide evidence for complex hybridization and demographic history in a group of Cycas from China. Frontiers in Genetics 12: 717200. doi:10.3389/fgene.2021.717200 [Admixture with Cycas bifida, Cycas balansae and Cycas changjiangensis.]
  • Nguyen, H.T. (2010). Cycas dolichophylla. The IUCN Red List of Threatened Species 2010: e.T42053A10639591. doi:10.2305/IUCN.UK.2010-3.RLTS.T42053A10639591.en [Previous assessment, NT A4cd according to The World List of Cycads; reference checked on Crossref.]
  • Bösenberg, J.D. (2023). Cycas dolichophylla. The IUCN Red List of Threatened Species 2023: e.T42053A68900008. doi:10.2305/IUCN.UK.2023-1.RLTS.T42053A68900008.en [Current assessment, NT; reference checked on Crossref, category confirmed by GBIF.]
  • Haynes, J.L. (2022). Etymological compendium of cycad names. Phytotaxa 550(1): 1–31. doi:10.11646/phytotaxa.550.1.1 [Etymology; cited 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. doi:10.5281/zenodo.21958524 [Reference checklist.]