Macrozamia cardiacensis

Macrozamia cardiacensis is a cycad from south-eastern Queensland, in eastern Australia, known only from Mount Walsh National Park near Biggenden, where it forms dense colonies on very steep slopes in open eucalypt forest. A species of the genus Macrozamia described in 1998, it carries a crown of 10 to 20 glossy, dark green leaves, 1 to 2 m long, on a trunk that usually stays underground, and it bears some of the largest cones of its group. Its name recalls Cardiac Hill, the slope down which botanists struggled to carry its heavy female cones. It is listed as Vulnerable.

Key facts about Macrozamia cardiacensis

  • Accepted name: Macrozamia cardiacensis P.I.Forst. & D.L.Jones (1998), accepted by The World List of Cycads (version 2026.08.15) and the Australian Plant Census
  • Former names and synonyms: none
  • Family: Zamiaceae, order Cycadales; section Macrozamia, Macrozamia miquelii group
  • Common names: no common name attested in English or any other language
  • Natural range: endemic to south-eastern Queensland, Australia: Mount Walsh National Park, near Biggenden (Wide Bay district), at 500 to 640 m
  • IUCN status: Vulnerable (VU D2), assessment by J.D. Bösenberg dated 13 August 2020 and published in 2022; Vulnerable under Queensland law
  • CITES and other protection: CITES Appendix II (annotation #4); Annex B in the European Union; not listed under Australia’s federal threatened-species law
  • Documented hardiness: no cultivation data (see Cold hardiness)
  • Light and soil: in the wild, open eucalypt forest on steep to precipitous slopes, in skeletal soils over rhyolite or andesite; in cultivation, not documented
  • Habit and adult size: trunk usually underground, sometimes emerging to 40 cm, 20 to 40 cm across; 10 to 20 leaves 1 to 2 m long
  • In the UK, US and Australia: seven plants of wild origin at the Royal Botanic Garden Sydney; no garden in the United Kingdom or the United States declares it to BGCI
  • Toxicity: not documented for the species; seeds and leaves toxic throughout the genus (see Toxicity and precautions)

How to recognise Macrozamia cardiacensis

It is recognised by its flat, arching, very glossy dark green leaves with a straight, untwisted axis, by the lowest leaflets that shrink step by step into numerous stiff spines, and above all by its large cones: the male cones reach 35 to 40 cm. The revision of the Macrozamia miquelii group by David Jones, Paul Forster and Ish Sharma (2001), based on living plants, describes it as follows.

  • Trunk: usually underground, sometimes emerging on rocky sites or in shallow soils, erect, columnar or barrel-shaped, up to 40 cm long and 20 to 40 cm across, unbranched.
  • Leaves: 10 to 20 in a moderately dense crown, 1 to 2 m long, obliquely erect to spreading, arching, dark green and glossy; petiole 30 to 40 cm long; axis straight, not twisted.
  • Leaflets: 100 to 140 per leaf, set at about 40° to the axis, crowded towards the tip of the leaf and more widely spaced towards its base, flat, 20 to 31 cm long and 8 to 12 mm wide, dark green and glossy above, paler beneath, with a pale yellow callus at the base and a sharp tip; the lowest four to seven pairs shrink gradually into rigid spines.
  • Male cones: one to five, cylindrical, 35 to 40 cm long and 6.5 to 8 cm across, green.
  • Female cones: one or two, narrowly ovoid, 32 to 36 cm long and 11 to 14 cm across, green; the scales near the top of the cone end in spines 4.5 to 5 cm long.
  • Seeds: oblong to ovoid, 2.2 to 3.5 cm long and 1.2 to 2 cm wide, with orange to dark red flesh.

The Flora of Australia (Hill, 1998, online through the ABRS) gives leaves 1.5 to 2 m long, leaflets 23 to 31 cm long and 9 to 11 mm wide, and 18 to 30 leaflets reduced to spines, which occupy up to the upper two-thirds of the petiole. It also notes the strongly two-toned leaflets, much paler beneath.

Hybrids

No natural or garden hybrid has been reported.

Possible confusion

Macrozamia cardiacensis belongs to the group of Macrozamia miquelii and looks much like that species at first sight. According to Jones et al. (2001), it differs from Macrozamia miquelii by its larger cones and by the longer spines on the scales near the top of the female cone.

It is even closer to Macrozamia douglasii, from K’gari (Fraser Island) and Cooloola, which has more leaves in the crown, a brilliant white callus at the base of each leaflet, only one to four pairs of spines and shorter spines at the top of the female cone scales. A partial analysis of enzymes (allozymes), based on few populations, supports this relationship. According to the Flora of Australia, Macrozamia cardiacensis also stands apart from the other species of the group by a petiole that carries spines over two-thirds of its length only, and by its large male and female cones.

Taxonomy

Macrozamia cardiacensis P.I.Forst. & D.L.Jones is accepted by The World List of Cycads and the Australian Plant Census, with no synonym. Paul Forster and David Jones described it in volume 48 of the Flora of Australia (1998, p. 717), and it was described again in detail in 2001 in the revision of the Macrozamia miquelii group, which recognises seven species in eastern Queensland.

This group belongs to section Macrozamia: medium-sized plants with untwisted or slightly twisted leaves, spiny petioles, stomata on the underside of the leaflets only, and lower leaflets that grade into spines (or, in a few species, no spines). The World List of Cycads places the species in the family Zamiaceae and does not use sections. The 2001 revision gives a key to the seven species: Macrozamia cardiacensis is the species in which eight or more of the lowest leaflets are reduced to spines and which combines narrowly ovoid female cones with male cones 35 to 40 cm long.

The type was collected on 26 February 1993 by Paul Forster and Peter Machin at Cardiac Hill, in Mount Walsh National Park (Forster 13109A); the holotype is held at the Queensland Herbarium in Brisbane. An older collection, made in May 1977 on Mount Walsh, 6.5 km south of Biggenden, is among the specimens cited in 2001.

Etymology and history

The epithet cardiacensis refers to the type locality, a very steep site known locally as Cardiac Hill. According to the authors, it also alludes to the hardship that the two collectors of the type experienced in carrying the heavy female cones of the species (Jones et al., 2001; Flora of Australia; Haynes, 2022, as given by The World List of Cycads). The genus name Macrozamia combines the Greek makros, “large”, with the genus name Zamia. No history of introduction into cultivation is documented.

A more detailed article on the species, by Paul Forster and Roy Osborne, appeared in 2003 in Encephalartos, the journal of the Cycad Society of South Africa (no. 75, pp. 8–13), according to The World List of Cycads.

Common names

No common name is attested for Macrozamia cardiacensis, in English or in any other language: the Flora of Australia, WildNet (the Queensland Government’s wildlife database) and the Atlas of Living Australia give none. The scientific name is used.

In the wild

Macrozamia cardiacensis is restricted to Mount Walsh National Park, near Biggenden, in the Wide Bay district of Queensland (Jones et al., 2001). It grows at 500 to 640 m, in skeletal soils derived from rhyolites or andesites, on steep to precipitous slopes, in open eucalypt forest with Eucalyptus andrewsii, Eucalyptus decolor, Eucalyptus acmenoides and Corymbia citriodora. The Flora of Australia names Eucalyptus acmenoides and Eucalyptus major instead. The species is locally abundant at its two known localities, in dense colonies with strong recruitment of seedlings. On rocky sites or in shallow soils, the plants often form an emergent trunk.

The male cones shed their pollen in November and December. In December 2000, Paul Forster observed both the thrips Cycadothrips chadwicki and a weevil of the genus Tranes on cones of both sexes: Macrozamia cardiacensis is the only species of the Macrozamia miquelii group on which these two pollinating insects have been seen together (Jones et al., 2001). Ripe seeds are shed from March to May. The Flora of Australia gives cones in February and March, without stating their stage.

Conservation status and regulation

Macrozamia cardiacensis is listed as Vulnerable (VU) on the IUCN Red List under criterion D2, which applies to species with a very small area of occupancy or very few locations. The assessment, by J.D. Bösenberg, is dated 13 August 2020 and was published in 2022 (The World List of Cycads, GBIF and Crossref, checked on 26 October 2026). WildNet also records an IUCN listing as Vulnerable from 2010.

In Queensland, its status has changed several times. In 2001 it was listed as Rare under the Nature Conservation Act 1992. WildNet then records it as Near Threatened from 2013 to 2015, and as Vulnerable in the current schedule of the Nature Conservation (Plants) Regulation 2020, as also stated by the Flora of Australia; it also flags it as a sensitive species. All known populations lie within Mount Walsh National Park. Neither WildNet nor the Atlas of Living Australia shows a listing under the federal Environment Protection and Biodiversity Conservation Act 1999 (EPBC).

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 before any purchase or import, and buy only seed-raised plants with their papers.

Growing Macrozamia cardiacensis

No published source describes the cultivation of Macrozamia cardiacensis, in Australia or elsewhere, and no English-language grower’s report has been found. Its natural habitat suggests a very free-draining, stony soil, the bright light of open forest, and a fairly large plant, with leaves 1 to 2 m long. These pointers are deduced from the habitat, not from trials.

Outdoor and in-ground cultivation

  • Light: bright, from full sun to the light shade of open eucalypt forest, as on Mount Walsh.
  • Soil: stony and very free-draining; in the wild, shallow skeletal soils on volcanic rock.
  • Space: allow for a crown of leaves up to 2 m long.
  • Water and feeding: no published data for the species.

Container cultivation

No container culture has been described. With leaves up to 2 m long, an adult plant needs a large, deep pot; a young plant is easier to manage. A plant in a pot loses the protection that the soil gives to its underground trunk in winter (see Cold hardiness).

In cultivation in the UK, US and Australia

  • Australia: the Royal Botanic Garden Sydney’s Garden Explorer lists seven plants of a wild-collected accession of 2022 (S2022-0082; updated 1 October 2026). It is not listed at the Australian Botanic Garden Mount Annan.
  • United States: no garden declares it to BGCI, and it is not in the online catalogue of Montgomery Botanical Center.
  • United Kingdom: no British garden declares it to BGCI.

In all, two institutions declare the species to BGCI (checked on 26 October 2026): the Royal Botanic Garden Sydney and Château Pérouse, in France. A BGCI listing records a declaration by the garden, not necessarily a living plant today.

Propagation

Macrozamia cardiacensis is propagated by seed. As the plants are male or female, both sexes are needed, and, in cultivation, hand pollination, to obtain fertile seed. No germination data specific to the species are documented. The trunk is unbranched and produces no known offsets. Wear gloves to clean off the flesh of the seeds, which is toxic.

Pests and diseases

No pest or disease specific to Macrozamia cardiacensis is documented. For Macrozamia grown in Europe, growers’ forums mainly mention scale insects and rot in cold, wet soil (see the genus page).

Cold hardiness

No cultivation result is documented for Macrozamia cardiacensis, anywhere in the world.

Mediterranean and European experience

No result has been published in Europe, in the ground or in a pot. In 2014, a member of the French Fous de palmiers forum relayed the ranking of an Australian cycad specialist, who placed Macrozamia cardiacensis among the “less hardy” species of inland Queensland, the third of his four groups, without giving a temperature.

United Kingdom, United States and Australia

No frost data have been published for Mount Walsh, and no hardiness rating, even commercial, has been found for the species. Any figure would be a guess, so none is given here. Until trials are published, a pot kept frost-free in winter is the prudent choice in Britain and in the colder parts of the United States.

Toxicity and precautions

No toxicity data specific to Macrozamia cardiacensis have been published, but 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 leaves can develop a locomotor disorder of the hind legs (Healy, 1967), which McKenzie (2006) describes as irreversible, ending in paralysis of the hindquarters, with no treatment.

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

Traditional uses

No traditional use specific to Macrozamia cardiacensis is documented. Other Macrozamia provided Aboriginal peoples with seeds that could be eaten after long processing (see the genus page).

Frequently asked questions

Where does the name cardiacensis come from?

From Cardiac Hill, the very steep slope where the type was collected. The authors also recall the effort it took the collectors to carry the heavy female cones down.

Where does it grow?

Only in Mount Walsh National Park, near Biggenden, in south-eastern Queensland. It forms dense colonies on steep slopes, between 500 and 640 m.

Is it endangered?

It is Vulnerable. The IUCN (2022) and Queensland list it as Vulnerable because of its very small range, even though it is abundant on the spot and protected in a national park.

How can it be told from Macrozamia miquelii?

By its cones. Those of Macrozamia cardiacensis are larger, the male cones reaching 35 to 40 cm, and the scales at the top of the female cones carry longer spines, 4.5 to 5 cm long.

What pollinates it?

Insects. A thrips (Cycadothrips chadwicki) and a weevil of the genus Tranes have been seen together on its cones, a unique case in its group of species.

Can it be grown in Britain or the United States?

Nobody knows yet. No grower has published any experience, and an Australian specialist ranks it among the less hardy Macrozamia; a pot kept frost-free in winter is the only prudent option.

Further reading on Succulentes

Sources

Reference sites

Bibliography

  • Forster, P.I. & Jones, D.L. (1998). Macrozamia cardiacensis. In: McCarthy, P.M. (ed.), Flora of Australia 48: 717. ABRS/CSIRO Publishing, Melbourne. [Protologue; reference from The World List of Cycads and Jones et al. (2001).]
  • Jones, D.L., Forster, P.I. & Sharma, I.K. (2001). Revision of the Macrozamia miquelii (F.Muell.) A.DC. (Zamiaceae section Macrozamia) group. Austrobaileya 6(1): 67–94. [Detailed description, type, habitat, pollinators, affinities, 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; online version.]
  • Forster, P.I. & Osborne, R. (2003). Focus on Macrozamia cardiacensis. Encephalartos 75: 8–13. [Article in the journal of the Cycad Society of South Africa, cited by The World List of Cycads.]
  • Healy, P.J. (1967). Macrozamia poisoning. Institute of Inspectors of Stock of New South Wales Year Book. [Reprinted by Flock & Herd.]
  • 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.]
  • Bösenberg, J.D. (2022). Macrozamia cardiacensis. The IUCN Red List of Threatened Species 2022: e.T41997A48715371. doi:10.2305/IUCN.UK.2022-1.RLTS.T41997A48715371.en [Vulnerable, criterion D2; assessment dated 13 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, as given 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 list.]