Cycas thouarsii R.Br. is the only Cycas native to Africa — and one of the most remarkable plants in the Indian Ocean basin. A towering arborescent cycad reaching 4–10 m, with fronds up to 3 m long and seeds the size of small plums, it occupies a vast but fragmented coastal range from the eastern shores of Madagascar through the Comoros, Mayotte, and Seychelles to mainland East Africa (Kenya, Tanzania, Mozambique). Its seeds, equipped with a unique spongy endocarp, float on ocean currents — a dispersal mechanism that has likely carried this species across thousands of kilometres of open water, colonising island after island over millions of years like a botanical message in a bottle.
Named in honour of the French botanist Louis-Marie Aubert du Petit-Thouars (1758–1831), who first encountered it during his explorations of the Mascarene Islands and Madagascar, Cycas thouarsii is the African representative of the buoyant-seeded Cycas rumphii complex — separated from its Indonesian sister species by the full width of the Indian Ocean, but connected to it by the same remarkable seed-floating adaptation. It is also, according to rarepalmseeds.com, “probably the oldest cycad, having been around for a possible 140 million years with little change in appearance” — and “undoubtedly the fastest growing cycad,” capable of reaching 60 cm in its first year from seed.
Taxonomy and nomenclature
First mentioned by Robert Brown in Prodromus Florae Novae Hollandiae (1810), initially confused with Cycas circinalis by Du Petit-Thouars himself in 1804. Family Cycadaceae, order Cycadales. Subsection Rumphiae. The species is most closely allied to Cycas rumphii from Southeast Asia and more distantly to Cycas circinalis from India — the three together forming the core of the buoyant-seeded complex. Previously treated as a subspecies of Cycas circinalis (Cycas circinalis subsp. thouarsii), it is now universally accepted as a distinct species.
Diagnostic features
Distinguished from its relatives by: distinctly bluish new leaves (a reliable field character absent in Cycas circinalis and Cycas rumphii); wholly spinescent petioles (spines along the entire length, not just the lower half); pronounced stout spines on the microsporophylls; and seeds that lack a crested sclerotesta (present in some other members of the complex).
Common names
Madagascar cycad, Madagascar sago (English); msikundazi (Swahili, East Africa).
Morphological description
Habit and caudex
A large, arborescent, dioecious, evergreen gymnosperm — one of the tallest species in the genus. The caudex is monopodial (single-trunked), well-developed, cylindrical, occasionally branching when old, reaching 3.5–10 m tall and up to 45 cm in diameter. In optimal conditions, this is a genuinely tree-sized cycad. The trunk is covered in persistent leaf bases and interspersed with brown, hairy, triangular cataphylls (scale-like protective leaves).
Leaves
Fronds are very large: 1.5–2.1 m long (occasionally to 3 m), 30–60 cm wide above the middle, flat in section, dark green, somewhat glossy above, paler beneath. Leaflets number 60–120 per side, each approximately 17 cm long, lanceolate, with a slightly recurved margin and a midrib more prominent on the lower surface. The petiole is 40–50 cm long with two rows of spines along nearly its whole length.
The most striking feature is the emerging flush: young fronds are distinctly blue-green — a glaucous tint that is absent in Cycas circinalis and Cycas rumphii and provides an instant identification character. As the fronds mature, they darken to the standard dark green.
Reproductive structures
Male cones are oblong-cylindrical to fusiform, 30–60 cm tall and 10–15 cm in diameter, orange to pale brown. The microsporophyll scales bear pronounced, upturned apical spines — stouter and more conspicuous than those of Cycas circinalis or Cycas rumphii. Female megasporophylls are 9–32 cm long, with 2–6 ovules each, and an ovate-lanceolate lamina with 12–16 short lateral spines.
Seeds — the largest in the genus
Cycas thouarsii produces the largest seeds in the genus Cycas, and among the largest of any gymnosperm: ovoid-globose, 50–60 mm long and approximately 40 mm wide. The sarcotesta is red to orange-brown. The endocarp is spongy — a pocket of buoyant tissue that allows the seed to float on seawater for extended periods without losing viability. This adaptation is the key to the species’ extraordinary geographic range: ocean currents have carried viable seeds across the Mozambique Channel (approximately 400 km from Madagascar to the African mainland) and between the widely separated islands of the western Indian Ocean.
LLIFLE notes that Cycas produces the largest ovules in the plant kingdom — up to 7 cm in Cycas thouarsii, exceeding even the 6 cm ovules of Cycas circinalis.
Distribution and natural habitat
Cycas thouarsii has the widest geographic range of any African cycad. It occurs on the east coast of Madagascar (where populations are most abundant); the Comoros archipelago; Mayotte; the Seychelles (including Aldabra Atoll); and scattered localities on the mainland East African coast from Mozambique through Tanzania (including Pemba Island) to Kenya. The total population is estimated at 10,000–15,000 mature individuals, with the population trend assessed as stable.
Some of the mainland African populations may have been established by Arab traders, who valued the plant for its beauty and food potential. However, certain stands appear pre-colonial and may represent natural arrivals via ocean-dispersed seed — the same mechanism that presumably brought the species to the Seychelles and Aldabra from Madagascar.
Habitat and climate
A strictly coastal and near-coastal species, growing from sea level to approximately 200 m elevation. Habitats include open coastal forests behind beaches, littoral woodland, sandy soils, and coral formations. Annual rainfall ranges from 1,000 to 3,000 mm depending on location. The climate is tropical maritime: warm and humid year-round, with no frost, and seasonal variation driven by monsoon rhythms rather than temperature. The species does not experience cold in its natural range.
Conservation status
IUCN Red List: Least Concern (LC), assessed 2020 by Bösenberg. Despite localised threats from agricultural expansion, coastal resort development, and collection for the ornamental trade, the overall population is considered stable and large enough to avoid a threatened classification. However, the assessment recommends continued monitoring and research into population dynamics. All Cycas species are listed in CITES Appendix II.
Cultivation guide
| Hardiness | Strictly tropical; frost-tender; minimum approximately 5–10 °C (USDA zone 10b–11) |
| Light | Full sun to partial shade; tolerates coastal exposure |
| Soil | Well-drained; sandy, coral-derived, or loamy |
| Water | Moderate; tolerates coastal humidity and salt spray |
| Growth rate | Fast — the fastest-growing Cycas species by some accounts |
| Mature size | 4–10 m; fronds to 3 m |
rarepalmseeds.com describes Cycas thouarsii as “the fastest growing cycad, reaching 60 cm in its first year from seed” — faster even than Cycas taitungensis, which is often given that title among cold-hardy species. Dave’s Garden contributors in zone 9a report that the species grows well in hot, humid, shaded positions with protection from frost, but fades in dry, sunny, exposed locations — it is not a xeric plant.
A Dave’s Garden contributor in zone 9b (presumably southern California or southern Florida) notes that frosts cause leaf damage but rarely kill established plants if mild and brief — however, it is fundamentally a tropical species and should not be expected to match the frost tolerance of Cycas revoluta or the hardy Chinese species.
Landscape use
Cycas thouarsii is one of the most impressive cycads available for tropical gardens. Its sheer size (eventually 10 m with 3 m fronds), fast growth, and bluish new flushes make it a commanding focal point. It excels in coastal tropical landscapes, botanical gardens, and estate-scale plantings. The species tolerates salt spray and sandy soils, making it well-suited to seaside gardens in frost-free zones.
Propagation
Seed: The large seeds are among the easiest cycad seeds to germinate. Clean the sarcotesta, soak, and plant at 25–30 °C. Germination is typically rapid for a cycad. Growth from seedling is fast — 60 cm of above-ground growth in the first year is documented. The seeds’ ability to float can be used as a viability test.
Pests and diseases
Aulacaspis yasumatsui is the primary pest threat wherever the species is grown outside its native range. Root rot from waterlogged substrates. The species is otherwise robust and trouble-free in its preferred tropical conditions.
Toxicity
All parts contain cycasin and BMAA. The large seeds are attractive to animals and children — caution is essential. In Madagascar and East Africa, the trunk pith and seeds have been processed as food (after extensive soaking and washing), following the same pattern documented across the Cycas rumphii complex.
The biogeographic story: Africa’s only Cycas
Cycas thouarsii is the sole representative of the genus Cycas on the African continent — a striking fact given that Africa hosts cycads from all three families (Cycadaceae, Zamiaceae, and Stangeriaceae), including the enormous genus Encephalartos (68+ species). The presence of Cycas only on the East African coast, not in the interior, strongly supports the hypothesis of relatively recent oceanic dispersal from Madagascar or from the broader Indo-Pacific via the Cycas rumphii lineage, rather than ancient Gondwanan vicariance. The spongy, buoyant seeds are the mechanism; the Indian Ocean currents are the vehicle.
This makes Cycas thouarsii a living demonstration of long-distance oceanic dispersal in a gymnosperm — a phenomenon more commonly associated with angiosperms like coconut palms. It is a biogeographic story of the first order, connecting the cycad floras of India, Indonesia, and Africa through a shared seed adaptation and the ocean currents of the Indian Ocean.
Authority websites
POWO — Plants of the World Online (Kew): https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:297046-1
IUCN Red List — Cycas thouarsii: https://www.iucnredlist.org/species/41940/10606292
LLIFLE: https://llifle.com/Encyclopedia/PALMS_AND_CYCADS/Family/Cycadaceae/28846/Cycas_thouarsii
rarepalmseeds.com: https://www.rarepalmseeds.com/cycas-thouarsii
Dave’s Garden: https://davesgarden.com/guides/pf/go/68350
The World List of Cycads: https://cycadlist.org/
Bibliography
Brown, R. (1810). Prodromus Florae Novae Hollandiae. First mention of Cycas thouarsii.
Hill, K.D. (1994). The Cycas rumphii complex (Cycadaceae) in New Guinea and the western Pacific. Australian Systematic Botany, 7(5), 543–567.
Golding, J. & Hurter, J. (2010). Cycas thouarsii. The IUCN Red List of Threatened Species.
Bösenberg, J.D. (2020). Cycas thouarsii reassessment. IUCN Red List.
Whitelock, L.M. (2002). The Cycads. Timber Press.
Rauh, W. (1995). Succulent and Xerophytic Plants of Madagascar, Vol. 1. Strawberry Press.
Prain, D. (1917). Flora of Tropical Africa, Vol. 6, Part 2, p. 344. — Cycas thouarsii in East Africa.
Dehgan, B. & Yuen, C.K.K.H. (1983). Seed morphology in relation to dispersal, evolution and propagation of Cycas. Botanical Gazette, 144(3), 412–418.