Cycas micronesica

Cycas micronesica is the cycad of the islands of western Micronesia: Guam, Rota and other islands of the Marianas, Yap and Palau. A member of the genus Cycas described in 1994, it had until then been confused with Cycas circinalis or Cycas rumphii, the names under which it appears throughout the medical literature on Guam. The most abundant tree on Guam in 2002, it collapsed there after an Asian scale insect, Aulacaspis yasumatsui, arrived in 2003: 96% of the plants monitored were dead by 2020. It is listed as Endangered by the IUCN and has been protected as a threatened species under United States law since 2015, which, as the Missouri Botanical Garden points out, makes it the only Cycas growing wild on land under US control. Its seeds are also at the heart of the hypothesis linking cycads to the neurological disease of the Chamorro people of Guam.

Key facts about Cycas micronesica

  • Accepted name: Cycas micronesica K.D.Hill (1994), 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: no formal synonym listed by The World List of Cycads; names misapplied before 1994: Cycas circinalis, Cycas rumphii; de Laubenfels and Adema (1998) placed it under Cycas celebica
  • Family: Cycadaceae, order Cycadales; subsection Rumphiae (Hill 1994)
  • Common names: fadang (Chamorro), faadang (Carolinian); “Federico nut” on the labels of the Royal Botanic Garden Sydney (see Common names)
  • Natural range: Guam, Northern Mariana Islands (Rota; also Tinian, and Pagan with doubt), Federated States of Micronesia (Yap), Palau
  • IUCN status: Endangered (EN A4ace), assessment by J. D. Bösenberg published in 2022, according to The World List of Cycads
  • CITES and other protection: CITES Appendix II (family listing, seeds exempt under annotation #4); Annex B in the European Union; listed as threatened under the US Endangered Species Act since 2 November 2015
  • Documented hardiness: no data; a species of frost-free tropical islands (see Cold hardiness)
  • Light and soil: in the wild, forest on Guam (coast below the limestone cliffs, northern plateau, southern ravines); growing requirements not documented
  • Habit and adult size: single-trunked tree; plants over 6 m tall measured on Guam, Tinian and Yap (Marler and colleagues 2020); male cones about 58 cm long before the scale invasion
  • In the UK, US and Australia: Montgomery Botanical Center (240 accessions, 1998 to 2026, many collected on Guam) and Missouri Botanical Garden (2022) in the United States; Royal Botanic Garden Sydney (three plants of wild origin, 1992); no British garden found
  • Toxicity: poisonous seeds; their role in the neurological disease of Guam is debated (see Toxicity and precautions)

How to recognise Cycas micronesica

Within its range, Cycas micronesica is easy to name: it is the only native cycad, a palm-like tree with a single trunk, and in 2002 it formed the most abundant tree population on Guam. Its detailed description is in Ken Hill’s protologue (1994), which could not be consulted; the measured data available come from studies carried out on Guam:

  • Height: Marler, Griffith and Krishnapillai (2020) followed the growth of plants from 1 m to more than 6 m tall on Guam, Tinian and Yap.
  • Growth: height growth is roughly constant whatever the size of the plant; female plants grow only 68% as fast as males.
  • Male cones: before the scale attacked them directly, they averaged 58 cm in height and 13 cm in diameter (Marler and Terry 2021).
  • Regrowth: when the terminal bud is killed or a trunk is snapped by a typhoon, adventitious buds form on the trunk, and fallen sections of trunk can take root (Deloso and colleagues 2020).

Hill (1994) placed it in the Cycas rumphii complex, which he was revising for New Guinea and the western Pacific. A French grower noted in 2009, on the Fous de palmiers forum, that its seeds were the largest he had seen in a Cycas, and the first leaf of his seedlings the biggest.

Hybrids

No hybrid of Cycas micronesica is known. As the only native cycad in its range, it meets other species only in gardens, notably Cycas revoluta, widely planted on Guam and Rota (Deloso and colleagues 2020).

Possible confusion

The most important confusion is historical. Until 1994, the cycads of Guam were called Cycas circinalis, a species from southern India, notably in Stone’s Flora of Guam (1970) and by Fosberg and Sachet (1975) (Lindström and Hill 2007). All the older medical papers on the “Guam cycad” and the neurological disease of the Chamorro people therefore concern Cycas micronesica. It was also referred to Cycas rumphii, an Indonesian species to which it is close. The 2015 US Federal Register notes that cycads seen on the island of Pagan were published as Cycas circinalis and are probably Cycas micronesica, without confirmation.

Taxonomy

Ken Hill described Cycas micronesica in 1994 in Australian Systematic Botany (7(6): 554–556, figure 10), in a revision of the Cycas rumphii complex in New Guinea and the western Pacific. That paper created subsection Rumphiae for the complex, described three new species (Cycas bougainvilleana, Cycas apoa and Cycas micronesica) and discussed the misapplication of the name Cycas circinalis in the western Pacific. The type is kept at the National Herbarium of New South Wales in Sydney (NSW).

In their revision of the genus, de Laubenfels and Adema (1998) placed these plants in the synonymy of Cycas celebica, a name that The World List of Cycads now refers to Cycas rumphii. The World List of Cycads and recent studies follow Hill and accept Cycas micronesica; the World Checklist of Vascular Plants (WCVP), on which POWO is based, also accepts it (consulted through GBIF on 31 October 2026). In practice, studies of the Guam disease published under the names Cycas circinalis or Cycas rumphii concern this species.

Etymology and history

The epithet micronesica refers to Micronesia, the region to which the species is endemic (Haynes 2022, after The World List of Cycads).

Before 2003 the plant was everywhere on Guam: a forest inventory of 2002 found it to be the island’s most abundant tree (Donnegan and colleagues 2004, cited by Marler and Terry 2021). The scale insect Aulacaspis yasumatsui was identified there in 2003 in a single urban garden, and on Rota in 2007; within a few years it had spread across the whole island, carried by the wild populations and by the many Cycas revoluta planted in towns (Deloso and colleagues 2020). The IUCN listed the species as Endangered as early as 2006, and the US Fish and Wildlife Service listed it as threatened on 1 October 2015, with effect from 2 November 2015.

Common names

The 2015 US Federal Register gives fadang in Chamorro, the indigenous language of Guam and the Marianas, and faadang in Carolinian. In English, the Royal Botanic Garden Sydney labels its plants “Federico nut”, a name not found in the other reference sources; it is best treated as a local or garden name. There is no other attested English name.

In the wild

The World List of Cycads places Cycas micronesica on Guam, Rota (Northern Mariana Islands), Yap (Federated States of Micronesia) and Palau. The 2015 Federal Register adds, with doubt, the island of Pagan, and mentions protective enclosures set up in 2013 on the island of Tinian, where plants are also monitored by Marler and colleagues (2020).

On Guam, the Federal Register describes four groups of populations, all in forest: on the northern coast up to the foot of the limestone cliffs, along the forest edge below those cliffs, on the northern plateau, and in the ravines and rocky outcrops of the south, with a few plants in savanna. In 2015 it put the total population at 900,000 to 950,000 individuals, fewer than 630,000 of them on Guam and Rota, about 288,450 on Yap and fewer than 2,500 on Palau, without separating young plants from breeding adults.

The plant is exposed to tropical cyclones. A healthy plant withstands them well thanks to its thick trunk, but the scale insect weakens trunks: Marler (2013) predicted more breakage, which typhoon Dolphin confirmed in May 2015 (Deloso and colleagues 2020). Marler and Niklas (2011) showed that plants exposed to wind and salt spray produce fewer ovules and seeds than those in sheltered sites. On Guam a genetic study (Cibrián-Jaramillo and colleagues 2010) revealed a mosaic of populations, with little exchange between the north and south of the island.

Conservation status and regulation

Cycas micronesica is listed as Endangered (EN A4ace) on the IUCN Red List, in the assessment by Bösenberg (2022) cited by The World List of Cycads; it had first been listed as Endangered in 2006 (Deloso and colleagues 2020), before the assessment by Marler, Haynes and Lindström (2010). The category is confirmed by the Red List data relayed by GBIF (consulted on 31 October 2026).

In the United States, the Fish and Wildlife Service listed it as threatened under the Endangered Species Act, by a rule published in the Federal Register on 1 October 2015 and effective on 2 November 2015, which covers 23 species of the Marianas and Micronesia. The rule cites the scale insect and other introduced animals, typhoons, urban development and damage from live-fire military training among the threats. In 2021 no recovery plan had yet been drawn up (Marler and Terry 2021).

Like all species of the family Cycadaceae, Cycas micronesica is listed in CITES Appendix II; Species+, the official CITES and EU database, shows it as a family-level listing with annotation #4 (CoP20 version, in force since 5 March 2026). This annotation exempts in particular seeds, pollen, and seedlings or tissue cultures obtained in vitro in sterile containers; live plants still require permits. In the European Union the species is in Annex B of Regulation (EC) No 338/97, in the version set by Commission Regulation (EU) 2026/1383, applicable since 29 June 2026. Species+ was consulted on 2 and 12 October 2026: check the regulations in force before any purchase, import or sale, and ask for proof that the plant was raised in cultivation. This information does not replace the official texts.

Growing Cycas micronesica

Cycas micronesica is hardly grown outside its range, and no growing data have been published beyond the studies carried out on Guam. These show that plants grow faster in managed gardens than in the wild (Marler and colleagues 2020). No requirement for soil, light or watering specific to the species is documented.

Outdoor and in-ground cultivation

The species comes from frost-free tropical islands, and outdoor cultivation is documented only in tropical or near-tropical gardens: Montgomery Botanical Center, in southern Florida, where cycads are grown outdoors, holds a large collection collected on Guam, and the Royal Botanic Garden Sydney has three plants in its beds. Neither garden has published growing observations on the species.

Container cultivation

In the United Kingdom and in most of the United States and Australia, only a heated glasshouse is suitable, which is a deduction from its frost-free range rather than a published trial. Grow only plants of legal, documented origin: the species is protected, and an infested plant can bring the scale insect into a collection.

In cultivation in the UK, US and Australia

The species is mainly an American conservation plant: the bulk of the ex situ collections are in the United States, where it is a federally threatened species. 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.

  • United States: the online catalogue of Montgomery Botanical Center (Coral Gables, Florida) lists 240 accessions, which their numbers date to 1998 (2), 2007 (63), 2025 (48) and 2026 (127); an article on the Missouri Botanical Garden collection illustrates a female plant at Montgomery collected from Guam (accession 20071020) (Deloso and colleagues 2025). The Missouri Botanical Garden (St Louis) added the species in 2022 (accession 2022-0953), describing it as “the only Cycas species found on US-controlled land” (Deloso and colleagues 2025). BGCI PlantSearch adds Naples Botanical Garden, the National Tropical Botanical Garden (Hawaii), the San Diego Zoo Botanical Gardens, The New York Botanical Garden, the Botanic Gardens at Kona Kai, the Center for Plant Conservation and the U.S. National Plant Germplasm System.
  • Australia: the online catalogue of the Royal Botanic Garden Sydney (updated on 1 October 2026) lists three plants of wild origin from the United States, accession S1992-0530, in beds 102j, 77 and 82c, under the name “Federico Nut”.
  • United Kingdom: no garden declares Cycas micronesica in BGCI PlantSearch, and it does not appear in the online garden catalogues.

No growing report has been published on English-language forums. The Jardin zoologique tropical at La Londe-les-Maures, in the south of France, has published no observation on this species.

Propagation

Propagation is from seed. No germination data have been published. A grower germinated seed in France in 2009 (Fous de palmiers forum), without detail on the conditions. In the wild, sections of trunk broken by typhoons can take root and regrow (Deloso and colleagues 2020), but there are no data on cuttings in cultivation. A male and a female plant are needed to obtain fertile seed.

Pests and diseases

The main enemy of Cycas micronesica is the Asian cycad scale, which has decimated the species on Guam; several other animals make its damage worse. Deloso and colleagues (2020) also report another scale insect, Pseudaulacaspis cockerelli, which settles mainly on the upper surface of the leaflets but does not form such dense infestations.

The scale insect Aulacaspis yasumatsui on Guam

Yes, this scale insect has almost wiped out Cycas micronesica on Guam, and the decline is one of the best documented for a plant invaded by an insect. The main stages have been published by Thomas Marler and his colleagues at the University of Guam:

  • In 2003 the scale is identified on Guam; until then the trees showed no insect damage on their leaves (Deloso and colleagues 2020).
  • In the west of the island, transects monitored from October 2004 to January 2011 were invaded four months after the first survey: all seedlings died within 9 months, all juveniles within about 40 months, and 92% of plants were dead six years after infestation (Marler and Lawrence 2012).
  • On 120 plots spread across the island since 2005, which started with about 1,600 seedlings, 1,160 juveniles and 1,240 adults per hectare, all seedlings were dead by 2006, all juveniles by 2014, and mortality reached 96% in 2020; two isolated localities in the west have disappeared entirely (Marler and Krishnapillai 2020).
  • On Yap, which the scale had not reached, juveniles and adults monitored from 2010 to 2018 remained stable (Marler and Krishnapillai 2020); the 2015 Federal Register reported the scale on Palau as early as 2008.
  • Height growth fell by 44% under insect attack, and the selective loss of young plants represents about 70 years of lost regeneration (Marler and colleagues 2020).
  • Male cones shrank after the infestation (24% of their original volume in 2007, 57% in 2021) and harbour fewer larvae of the pollinating moth, which threatens that pollinator too (Marler and Terry 2021).

According to Deloso and colleagues (2020), the scale is the only pest able to kill the tree on its own: it colonises every organ, from roots to seeds, and exhausts the plant’s reserves. Its severity on Guam comes from the lack of effective natural enemies. The ladybird Rhyzobius lophanthae, released in 2005, does not control the scale in the recesses of the plant or near the ground; the parasitoids introduced did not establish, and a small parasitoid that arrived by itself in 2013 attacks only males. Other pests add to the damage: the cycad blue butterfly, Luthrodes pandava (also known as Chilades pandava), on Guam since 2005; a leaf-mining caterpillar (Erechthias); a native longhorn beetle that bores into weakened trunks; feral pigs, which now gnaw standing trunks; and, since 2020, the coconut rhinoceros beetle, Oryctes rhinoceros.

The lesson for growers elsewhere is direct: the scale travels with cultivated plants. In Europe, the EPPO database (update of 16 October 2026) lists it as present, with few occurrences, in several countries including the United Kingdom. Check the leaf bases and trunk of any cycad you buy.

Cold hardiness

No cold-tolerance value has been published for Cycas micronesica. The available studies deal with heat, typhoons and insects, not with cold, and no growing report gives a winter temperature. The species grows on tropical islands where frost does not occur. In the United Kingdom and in most of the United States and Australia, keep it frost-free under glass; outdoors, it has been planted only in tropical and near-tropical gardens such as those of southern Florida and Sydney.

Toxicity and precautions

Yes, the seeds of Cycas micronesica are poisonous, like those of all Cycas. In the genus, all parts of the plant contain cycasin, which is converted in the body into methylazoxymethanol, toxic to the liver and nervous system, along with a neurotoxic amino acid, BMAA (NC State Extension; ASPCA). In dogs, cats and horses, the ASPCA reports digestive upset, liver damage and fatal cases.

On Guam, flour made from the seeds was long suspected of causing a neurological disease that was very common among the Chamorro people, combining amyotrophic lateral sclerosis and parkinsonism with dementia (known locally as lytico-bodig). Cox and Sacks (2002) proposed that the toxins build up in flying foxes, fruit bats eaten locally; Steele and McGeer (2008) consider that the cycad hypothesis does not meet the necessary criteria and that other causes must be considered. The link remains debated. Marler and colleagues have studied the sterol glucosides of the seeds, compounds under suspicion, and the standards needed to measure them (Marler and colleagues 2005).

Wear gloves to handle seeds and their fleshy coat, pick up any that fall, and keep plants and seeds 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

The seeds were used as food on Guam after a long detoxification process; it is this use that lies at the centre of the hypothesis about the Guam disease. The dates and methods of preparation have not been checked in a primary source, so they are not detailed here. These preparations must not be copied.

Frequently asked questions

Why has Cycas micronesica almost disappeared from Guam?

Because of the scale insect Aulacaspis yasumatsui, which arrived in 2003. With no effective natural enemy, it killed all the seedlings and juveniles, then most of the adults: 96% mortality by 2020 on the plots monitored.

Are Cycas micronesica and Cycas circinalis the same plant?

No. Cycas circinalis comes from southern India. The name was wrongly applied to the cycads of Guam until Cycas micronesica was described in 1994.

Does the Guam cycad cause ALS?

That has not been established. The hypothesis linking the seeds to the neurological disease of the Chamorro people has been put forward and remains debated; other causes are being considered.

Is it protected?

Yes. It is listed as Endangered by the IUCN, in CITES Appendix II, and as a threatened species under the US Endangered Species Act since 2015.

Where can I see it outside Micronesia?

Mainly in the United States, at Montgomery Botanical Center in Florida, which holds a large collection collected on Guam, and at the Missouri Botanical Garden; in Australia, at the Royal Botanic Garden Sydney. No British garden lists it.

Can it be grown outdoors?

Only in frost-free tropical or near-tropical climates. Elsewhere it needs a heated glasshouse, and no growing data have been published.

Is the Guam scale insect present in Europe?

Yes, in a few countries. The EPPO database lists it with few occurrences in several European countries, including the United Kingdom; inspect any cycad you buy.

Further reading on Succulentes

Sources

Reference sites

Bibliography

  • Hill, K.D. (1994). The Cycas rumphii complex (Cycadaceae) in New Guinea and the western Pacific. Australian Systematic Botany 7(6): 543–567. doi:10.1071/SB9940543 [Protologue (pages 554–556); creation of subsection Rumphiae.]
  • Lindström, A.J. & Hill, K.D. (2007). The genus Cycas (Cycadaceae) in India. Telopea 11(4): 463–488. doi:10.7751/telopea20075745 [Misapplication of Cycas circinalis on Guam (Stone 1970; Fosberg and Sachet 1975).]
  • Marler, T.E. & Lawrence, J.H. (2012). Demography of Cycas micronesica on Guam following introduction of the armoured scale Aulacaspis yasumatsui. Journal of Tropical Ecology 28(3): 233–242. doi:10.1017/S0266467412000119 [92% mortality six years after infestation.]
  • Marler, T.E. & Krishnapillai, M.V. (2020). Longitude, forest fragmentation, and plant size influence Cycas micronesica mortality following island insect invasions. Diversity 12(5): 194. doi:10.3390/d12050194 [96% mortality in 2020, comparison with Yap.]
  • Deloso, B.E., Terry, L.I., Yudin, L.S. & Marler, T.E. (2020). Biotic threats to Cycas micronesica continue to expand to complicate conservation decisions. Insects 11(12): 888. doi:10.3390/insects11120888 [History of the invasions and ranking of threats; peer-reviewed article.]
  • Marler, T.E. & Terry, L.I. (2021). Aulacaspis yasumatsui invasion reduced Cycas micronesica microstrobilus size and pollinator brood site competence. Insects 12(11): 1023. doi:10.3390/insects12111023 [Size of male cones, pollinator, federal status.]
  • Marler, T.E., Griffith, M.P. & Krishnapillai, M.V. (2020). Height increment of Cycas micronesica informs conservation decisions. Plant Signaling & Behavior 15(12): 1830237. doi:10.1080/15592324.2020.1830237 [Height growth on Guam, Tinian and Yap.]
  • Marler, T.E. (2013). Increased threat of island endemic tree’s extirpation via invasion-induced decline of intrinsic resistance to recurring tropical cyclones. Communicative & Integrative Biology 6(1): e22361. doi:10.4161/cib.22361 [Resistance to typhoons.]
  • Marler, T.E. & Niklas, K.J. (2011). Reproductive effort and success of Cycas micronesica K.D. Hill are affected by habitat. International Journal of Plant Sciences 172: 700–706. doi:10.1086/659455 [Effect of wind and salt spray.]
  • Cibrián-Jaramillo, A., Daly, A.C., Brenner, E., DeSalle, R. & Marler, T.E. (2010). When North and South don’t mix: genetic connectivity of a recently endangered oceanic cycad, Cycas micronesica, in Guam using EST-microsatellites. Molecular Ecology 19: 2364–2379. doi:10.1111/j.1365-294X.2010.04638.x [Genetic structure on Guam.]
  • Marler, T.E., Lee, V. & Shaw, C.A. (2005). Cycad toxins and neurological diseases in Guam: defining theoretical and experimental standards for correlating human disease with environmental toxins. HortScience 40(6): 1598–1606. [Reference taken from The World List of Cycads.]
  • Cox, P.A. & Sacks, O.W. (2002). Cycad neurotoxins, consumption of flying foxes, and ALS-PDC disease in Guam. Neurology 58(6): 956–959. doi:10.1212/WNL.58.6.956 [Flying-fox hypothesis; reference checked on Crossref.]
  • Steele, J.C. & McGeer, P.L. (2008). The ALS/PDC syndrome of Guam and the cycad hypothesis. Neurology 70(21): 1984–1990. doi:10.1212/01.wnl.0000312571.81091.26 [Critique of the cycad hypothesis.]
  • U.S. Fish and Wildlife Service (2015). Endangered and threatened wildlife and plants; endangered status for 16 species and threatened status for 7 species in Micronesia. Federal Register 80: 59424–59497. [Listing rule.]
  • Deloso, B.E., Colligan, A., Sucher, R. & Ramirez, V. (2025). Missouri Botanical Garden’s cycad collection: a journey through time. Plant Species Biology. doi:10.1111/1442-1984.12509 [Accession 2022-0953, “only Cycas species found on US-controlled land”, plants collected from Guam at Montgomery.]
  • Laubenfels, D.J. de & Adema, F. (1998). A taxonomic revision of the genera Cycas and Epicycas gen. nov. (Cycadaceae). Blumea 43(2): 351–400. [Treatment under Cycas celebica; reference taken from The World List of Cycads.]
  • Haynes, J.L. (2022). Etymological compendium of cycad names. Phytotaxa 550(1): 1–31. doi:10.11646/phytotaxa.550.1.1 [Etymology of the epithet; 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.]