Macrozamia platyrhachis

Macrozamia platyrhachis is a cycad with no visible trunk from central Queensland, in eastern Australia, confined to the Blackdown Tableland and the Expedition Range, where it grows in dry eucalypt forest on sandstone plateaus. This species of the genus Macrozamia is recognised by its few short, recurved leaves with a broad, flattened axis, carrying the widest leaflets of any small Macrozamia, up to 2 cm. Described in 1898 by Frederick Manson Bailey under the spelling Macrozamia platyrachis, still used by some authors, it is listed as Endangered by the IUCN and under Australian law.

Key facts about Macrozamia platyrhachis

  • Accepted name: Macrozamia platyrhachis F.M.Bailey (1898), accepted by The World List of Cycads (version 2026.08.15) and the Australian Plant Census
  • Former names and synonyms: no synonym; original spelling Macrozamia platyrachis, kept by L.A.S. Johnson (1959) and in a text published by PACSOA
  • Family: Zamiaceae, order Cycadales; section Parazamia
  • Common names: “Blackdown zamia palm” (Australian Plant Census, through the Atlas of Living Australia)
  • Natural range: central-eastern Queensland, Australia: Blackdown Tableland and Expedition Range
  • IUCN status: Endangered (EN B1ab(i,ii,iii,v)), assessment by P.I. Forster and I. Terry dated 20 August 2020 and published in 2022
  • CITES and other protection: CITES Appendix II (annotation #4); Annex B in the European Union; Endangered under the federal EPBC Act and under Queensland law
  • Documented hardiness: no data (see Cold hardiness)
  • Light and soil: in the wild, dry sclerophyll forest on sandstone plateaus, deep sandy loams; in cultivation, a very open, free-draining mix (see Growing)
  • Habit and adult size: underground stem 25 to 60 cm across; 2 to 8 leaves (up to about ten) 45 to 80 cm long, sometimes close to 1 m
  • In the UK, US and Australia: declared to BGCI by the Australian National Botanic Gardens in Canberra, the North Coast Regional Botanic Garden in Coffs Harbour, the Los Angeles County Arboretum and Montgomery Botanical Center; no British garden
  • Toxicity: no data for the species; an old remark that it does not poison cattle has never been confirmed (see Toxicity and precautions)

How to recognise Macrozamia platyrhachis

It is the only small Macrozamia to combine a short, broad petiole, an axis flattened above and angular beneath, and stiff leaflets 12 to 20 mm wide. The Flora of Australia (Hill, 1998) distinguishes it by its short leaves with short, broad petioles and very broad leaflets. Its measurements are as follows.

  • Stem: underground, 25 to 60 cm across.
  • Leaves: 2 to 8 in the crown, 45 to 80 cm long, moderately keeled, mid-green, semi-glossy to very glossy; petiole 15 to 25 cm long, 13 to 18 mm wide at the lowest leaflet.
  • Leaflets: 36 to 60 per leaf, simple, 25 to 40 cm long and 12 to 20 mm wide, clearly paler beneath, with flat margins and an entire or toothed tip; the lowest leaflets are not reduced to spines; Johnson (1959) counted 15 to 18 raised veins beneath.
  • Male cones: narrowly ovoid, 15 to 20 cm long and 4 to 4.5 cm across.
  • Female cones: ovoid, 12 to 17 cm long and 8 to 9 cm across, with terminal spines 1 to 13 mm long.
  • Seeds: ovoid, 25 to 30 mm long and 20 to 25 mm wide, with red flesh.

The sources disagree on the twisting of the leaf axis. The Flora of Australia describes it as moderately to strongly spirally twisted and speaks of short, spirally twisted leaves. David Jones (1991), and then Jones and Forster (1994) in their key, describe instead recurved leaves, almost lying horizontal, with an axis “scarcely twisted”, sharply bent near the base, and erect leaflets; Johnson (1959) wrote “not or moderately twisted”. In a text of 1994 reproduced by PACSOA, a grower describes a plant with four leaves that rise from the crown and then curve over very markedly, shiny and leathery; the largest plants in the wild, he adds, carry nine or ten leaves up to a metre long.

Hybrids

No natural or garden hybrid has been documented. The geographical isolation of the species, the most northerly of section Parazamia, makes natural crosses unlikely, but no source states this.

Possible confusion

Its very broad leaflets make it hard to mistake, especially when its origin is known.

  • Macrozamia fearnsidei: the species of section Parazamia geographically closest to it, but not its closest relative according to Jones (1991); more robust, with up to 20 erect leaves and a clearly twisted axis.
  • Macrozamia fawcettii: another broad-leaflet species, from northern New South Wales; Schuster (1932) linked the two, but Johnson (1959) saw only a convergence.
  • Macrozamia miquelii and the other species of section Macrozamia in the region: larger, with their lowest leaflets reduced to spines.

Taxonomy

Macrozamia platyrhachis F.M.Bailey is accepted by The World List of Cycads and the Australian Plant Census. It belongs to section Parazamia, that of the small species with an underground stem, no spiny leaflets and no mucilage canals. Johnson (1959) considered it “little known but quite distinct” and attached it to no subgroup of the section; Jones and Forster (1994) place it in the “Macrozamia plurinervia complex”, with fairly broad, shallowly channelled leaflets. It has never changed genus or species.

Only its spelling varies. Bailey published the name in 1898 as platyrachis, then wrote platyrhachis from 1902 in his Queensland Flora, without presenting the change as a correction. Johnson (1959) held that the original spelling should be kept, and the PACSOA text still uses it. The World List of Cycads, the Flora of Australia, Species+ and the Australian Plant Census use platyrhachis, the form followed here; the two spellings refer to the same plant.

Etymology and history

The epithet comes from the Greek platys, “broad”, and rhachis, “leaf axis above the petiole”, and refers to the strongly flattened axis (The World List of Cycads, after Haynes, 2022). According to the PACSOA text, the leaflets are also noticeably broader than in any other species of the section.

Bailey described the plant in 1898 in the Queensland Agricultural Journal (vol. 3, p. 356), from a male plant sent, with a female cone, by H.C. Brock-Hollinshead from a range near Planet Downs (holotype in the Queensland Herbarium, BRI; isotype in Sydney, NSW). Johnson (1959) listed two points of Bailey’s description that needed confirming: the absence of wool at the leaf bases, and the collector’s remark that the plant does not cause “rickets”, the paralysis of cattle. The PACSOA text suggests that the species was discovered later than the others precisely because it did not seem dangerous to livestock, so that nothing drew graziers’ attention to it. It remains little grown.

Common names

The Australian Plant Census, as shown by the Atlas of Living Australia, gives the English name “Blackdown zamia palm”, after the plateau where it lives; the plant is, of course, not a palm. No Aboriginal name is recorded.

In the wild

According to the Flora of Australia, the species is endemic to central-eastern Queensland, on the Blackdown Tableland and in the Expedition Range, where it is scattered but locally abundant in dry sclerophyll forest on flat sandstone plateau country. It is the most northerly Macrozamia of section Parazamia.

The PACSOA text (1994) describes the Blackdown Tableland, west of Rockhampton and a little south of Dingo, as hilly country with steep escarpments, rising from 500 m to nearly 1,000 m, most of it declared a national park in 1982. The soils are mainly deep sandy loams; the eucalypt forest grows alongside a palm endemic to the plateau, Livistona fulva. The finest colonies are on the western side, among huge sandstone boulders, with a eucalypt known as “yellow jacket” and Grevillea longistylis; the boulders carry the silver elkhorn fern Platycerium veitchii and Drynaria rigidula. A photograph on the same page, taken in a July (year not stated), shows a fine colony with plenty of seedlings.

The most thorough study is that of Irene Terry and her colleagues (2008), carried out to reassess the status of the species. They surveyed 11 discrete populations, locally abundant, with an estimated total of about 611,000 adult plants. But the species occupies a very small area, its seeds hardly disperse, and extreme fires appear to have destroyed almost all seeds and seedlings and decimated the pollinators. The only pollinator found on the cones was a tiny thrips, Cycadothrips chadwicki, in very low numbers. The cones produce heat with a peak in the early evening, whereas in the other Macrozamia pollinated by this thrips the peak occurs during the day; this timing matches that of Macrozamia machinii, which is pollinated by a weevil. Its cone scents likewise combine compounds known from both types of pollination, along with others never reported before. The authors consider this pollination syndrome unique.

The Flora of Australia adds that these plants live in an extremely fire-prone habitat, burnt irregularly every two years or more, and that the seeds ripen in March and April.

Conservation status and regulation

Macrozamia platyrhachis is listed as Endangered (EN) on the IUCN Red List under criteria B1ab(i,ii,iii,v): its range is very small, severely fragmented or limited to few locations, with a continuing decline in extent of occurrence, area of occupancy, habitat quality and number of plants. The assessment, by P.I. Forster and I. Terry, is dated 20 August 2020 and was published in 2022 (The World List of Cycads, GBIF and Crossref, checked on 26 October 2026). The species is also listed as Endangered under the federal Environment Protection and Biodiversity Conservation Act 1999 (EPBC), effective 16 July 2000, and under the Queensland Nature Conservation (Plants) Regulation 2020, according to the Flora of Australia and the Atlas of Living Australia. It is covered by a national recovery plan shared by six cycads (Queensland Herbarium, 2007).

Terry and her colleagues (2008) recommended keeping this status, because of the small area occupied, the expected declines and the unique pollination syndrome, and asked that controlled burns avoid the coning season and that wildfires be controlled to protect seedlings and pollinators. According to the PACSOA text (1994), national park status and difficult access, along a long unsealed road, help to protect the species; enthusiasts then obtained large plants legally from the owners of farms bordering the plateau.

Like other Macrozamia, it has been listed in CITES Appendix II since 4 February 1977, with annotation #4: seeds and pollen are exempt, but plants are not. In the European Union it falls under Annex B of Regulation (EC) No 338/97, as amended by Regulation (EU) 2026/1383, applicable since 29 June 2026 (Species+, checked on 26 October 2026). Check the regulations in force, and the customs and plant-health rules, before any purchase abroad, and buy only seed-grown plants of known origin.

Growing Macrozamia platyrhachis

The species is rarely grown, and the only published cultivation experience concerns the potting mix: it must drain perfectly and be very open.

In a note added to the PACSOA page, the editor of the society’s journal recalls receiving plants in poor condition, grown in a sawdust-based mix with very poor air-filled porosity: several had died and most had diseased or dead roots. Repotted into a mix based mainly on pine bark, which suits many cycads, they kept declining; only after a second repotting into a mix composed mainly of perlite, with a little coir, did they recover and form good roots. He concludes that perfect drainage and a good supply of air to the roots are of utmost importance for this species. This is a single experience, in Australia and in pots.

Outdoor and in-ground cultivation

  • Soil: very mineral, free-draining and open (perlite, pumice, coarse sand); a deep pot or bed suits the large underground stem.
  • Light: in the wild, open eucalypt forest; a bright position suits it. Its tolerance of full sun in Europe is not documented.
  • Water: water during growth and let the mix dry between waterings; the experience reported by PACSOA shows that the roots do not tolerate a mix that stays wet and compact.
  • Growth: raising mature plants from seed “takes a long time”, according to the PACSOA text.

Container cultivation

The only documented experience is in pots: a mix composed mainly of perlite, with a little coir, gave good roots where sawdust-based and pine-bark mixes failed. Use a deep pot with a large drainage hole.

In cultivation in the UK, US and Australia

  • Australia: the Australian National Botanic Gardens (Canberra) and the North Coast Regional Botanic Garden (Coffs Harbour, New South Wales) declare it to BGCI; neither the Royal Botanic Garden Sydney nor Mount Annan lists it in its online catalogue.
  • United States: the Los Angeles County Arboretum and Botanic Garden (Arcadia, California) and Montgomery Botanical Center (Coral Gables, Florida) declare it to BGCI; Montgomery’s online catalogue, however, lists no accession under this name. A BGCI declaration says that a garden has held the plant, not that a living specimen is there today.
  • United Kingdom: no British garden declares it to BGCI (checked on 26 October 2026).

No dated cultivation report has been published on English-language forums that can be read.

Propagation

Propagation is by seed; in the wild the seeds ripen in March and April. Plants are male or female: both sexes are needed and, in cultivation, hand-pollination is required to obtain fertile seed. No germination data specific to the species have been published. An Italian grower noted on the Tropicamente forum in 2009 that the seeds were hard to find.

Pests and diseases

The only documented problem is root rot in a poorly aerated mix (see Growing). For Macrozamia grown in Europe, growers’ forums also mention scale insects (see the genus page).

Cold hardiness

No data exist: no cultivation report, and no published climate record for its habitat.

Mediterranean and European experience

No cultivation of the species has been reported in France or elsewhere in Europe. On the French Fous de palmiers forum, a grower listed it in 2012 among the small Macrozamia that are “much harder to find”, and in March 2014 reported the opinion of an Australian nurseryman specialising in cycads, who placed it among the “least hardy” species of inland Queensland, without giving temperatures.

United Kingdom, United States and Australia

No dated report exists on the English-language forums that can be read. The altitude of the Blackdown Tableland, up to nearly 1,000 m, is not enough to infer any frost tolerance: no published source gives minimum temperatures for its habitat. In Britain and in the colder parts of the United States, a pot kept frost-free in winter is the prudent choice.

Toxicity and precautions

No toxicity data specific to Macrozamia platyrhachis have been published. The collector of the type stated in 1898 that the plant does not paralyse cattle, but Johnson (1959) considered this remark in need of confirmation, and no study has tested it since: it would be unwise to conclude that the plant is harmless. The risk is well documented for the genus. Macrozamia contain toxic glycosides (cycasin, macrozamin), from which methylazoxymethanol is derived, a poison of the liver; cattle that eat the young leaves can develop a locomotor disorder of the hindquarters, which McKenzie (2006) describes as irreversible, with no treatment (see the genus page).

Wear gloves to handle the seeds, keep them out of reach of children, dogs and livestock, and contact a poison centre, a doctor or a vet without delay in case of ingestion.

Traditional uses

No use specific to Macrozamia platyrhachis is documented. Asmussen’s (2011) review of the eating of Macrozamia seeds by Aboriginal peoples does not mention this species (see the genus page).

Frequently asked questions

Should it be spelt platyrhachis or platyrachis?

Both refer to the same plant. Bailey wrote platyrachis in 1898, then platyrhachis from 1902; The World List of Cycads, the Flora of Australia and Species+ use platyrhachis, while Johnson (1959) and the PACSOA text keep platyrachis.

How can it be recognised?

By its very broad leaflets, 12 to 20 mm wide, stiff and glossy, carried by a few short, recurved leaves with a short, broad petiole and a flattened axis. No other small Macrozamia has leaflets as broad.

Is it endangered?

Yes. It is listed as Endangered by the IUCN (assessment published in 2022), under Australian federal law and in Queensland. Despite about 611,000 adults counted in 2008, the area it occupies is very small and fires destroy seeds and seedlings.

What pollinates it?

A tiny thrips, Cycadothrips chadwicki, found in very low numbers on the cones in 2008. The cone heats up mainly in the early evening, a behaviour the researchers consider unique among the Macrozamia pollinated by this thrips.

Is it difficult to grow?

It is above all demanding about its potting mix. The only published experience shows that its roots rot in a compact or poorly aerated mix and recover in a mix made mostly of perlite.

How hardy is it?

Nobody knows. No cultivation report or climate data for its habitat have been published; an Australian nurseryman, quoted on a French forum, ranks it among the least hardy Macrozamia, without figures.

Is it poisonous?

Probably, like all Macrozamia. An 1898 remark said it did not affect cattle, but it has never been confirmed; handle the seeds and young leaves with care.

Further reading on Succulentes

Sources

Reference sites

Bibliography

  • Bailey, F.M. (1898). Contributions to the flora of Queensland. Queensland Agricultural Journal 3: 353–356 (p. 356 for this species). [Original description, under the spelling platyrachis; reference as given by The World List of Cycads.]
  • Johnson, L.A.S. (1959). The families of cycads and the Zamiaceae of Australia. Proceedings of the Linnean Society of New South Wales, ser. 2, 84(1): 64–117 (pp. 101–102 for this species). [Typification, description after Bailey, spelling, affinities, remark on cattle; full text (PDF made available by The World List of Cycads).]
  • Jones, D.L. (1991). Notes on Macrozamia Miq. (Zamiaceae) in Queensland with the description of two new species in section Parazamia (Miq.) Miq. Austrobaileya 3(3): 481–487. [Distinction from Macrozamia fearnsidei, key; full text (BioStor).]
  • Jones, D.L. & Forster, P.I. (1994). Seven new species of Macrozamia section Parazamia (Miq.) Miq. (Zamiaceae section Parazamia) from Queensland. Austrobaileya 4(2): 269–288. [Place of the species in the Macrozamia plurinervia complex, key; full text.]
  • Hill, K.D. (1998). Cycadophyta. In: McCarthy, P.M. (ed.), Flora of Australia 48: 597–661, 717–719. ABRS/CSIRO Publishing, Melbourne. [Description and range; online version.]
  • Terry, L.I., Forster, P.I., Moore, C.J., Roemer, R.B. & Machin, P.J. (2008). Demographics, pollination syndrome and conservation status of Macrozamia platyrhachis (Zamiaceae), a geographically restricted Queensland cycad. Australian Journal of Botany 56(4): 321–332. doi:10.1071/BT06202 [Numbers, threats, pollination, thermogenesis, recommendations; abstract read through Crossref.]
  • Terry, I., Walter, G.H., Donaldson, J.S., Snow, E., Forster, P.I. & Machin, P.J. (2005). Pollination of Australian Macrozamia cycads (Zamiaceae): effectiveness and behavior of specialist vectors in a dependent mutualism. American Journal of Botany 92(6): 931–940. doi:10.3732/ajb.92.6.931 [Thrips pollination, as cited by the Flora of Australia.]
  • Queensland Herbarium (2007). National Multi-species Recovery Plan for the cycads, Cycas megacarpa, Cycas ophiolitica, Macrozamia cranei, Macrozamia lomandroides, Macrozamia pauli-guilielmi and Macrozamia platyrhachis. Department of the Environment and Water Resources, Canberra. [Recovery plan, as cited by the Flora of Australia.]
  • Osborne, R. (2000). Focus on Macrozamia platyrachis. Encephalartos 61: 4–8. [Reference as given by The World List of Cycads.]
  • Forster, P.I. & Terry, I. (2022). Macrozamia platyrhachis. The IUCN Red List of Threatened Species 2022: e.T42016A50524767. doi:10.2305/IUCN.UK.2022-1.RLTS.T42016A50524767.en [Endangered, criteria B1ab(i,ii,iii,v); assessment dated 20 August 2020, from Crossref.]
  • 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, as given by The World List of Cycads.]
  • Asmussen, B. (2011). “There is likewise a nut…” a comparative ethnobotany of Aboriginal processing methods and consumption of Australian Bowenia, Cycas, Macrozamia and Lepidozamia species. Technical Reports of the Australian Museum, Online 23(10): 147–163. doi:10.3853/j.1835-4211.23.2011.1575 [Aboriginal uses; the species is not mentioned.]
  • McKenzie, R.A. (2006). Toxicology for Australian Veterinarians: cycads (Cycas, Macrozamia, Lepidozamia, Bowenia), pp. 282–288. Animal Health Australia, Australian Animal Pathology Standards Program (PDF): https://aapspextranet.animalhealthaustralia.com.au/wp-content/uploads/2019/04/tav7_17_unknowntoxins_pt2.pdf [Australian veterinary reference text; describes the cattle syndrome as irreversible, ending in paralysis of the hindquarters, with no treatment.]
  • 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 list.]