The Spiny Desert and the Octopus Trees

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By Jordan Lamont · Last updated 7 October 2026

Step into the far south of Madagascar and you step onto what looks like another world: a grey-green desert bristling with thorns, where trees wave long spiny arms like frozen octopuses and nothing you recognise grows at all. The spiny forest is one of the strangest plant communities on Earth — and almost everything in it lives nowhere else. It is Madagascar’s endemism turned up to its absolute maximum.

A desert of plants found nowhere else

The spiny forests of southwest Madagascar are a hot, dry ecoregion that holds the highest plant endemism on the island: around 95% of the species and nearly half the genera grow only here. It is simultaneously one of the world’s most unique and most endangered habitats — a living laboratory of how plants survive where rain almost never falls.

The octopus tree and its cousins

The signature plants belong to the Didiereaceae, a family found nowhere on Earth but Madagascar. They look uncannily like cacti — tall, columnar, armoured in thorns — yet they are unrelated to true cacti, a classic case of convergent evolution. The most famous is the octopus tree (Didierea madagascariensis), whose long, writhing, spine-covered arms give it its name, alongside the ocotillo-like Alluaudia. Among them grow spiny euphorbias and a cast of other drought specialists.

Built to survive on nothing

Everything here is an answer to drought. Spiny-forest plants store water in swollen succulent trunks and branches, send down massive underground tubers, shrink their leaves to tiny or deciduous scraps, and armour themselves with thorns against the few animals desperate enough to eat them. Many wear waxy or hairy coatings to slow evaporation. The result is a landscape that looks hostile and dead but is, in fact, a masterpiece of botanical engineering.

Why it matters today

The spiny forest is Madagascar’s evolution at its most extreme — and among its most threatened, as charcoal-cutting and clearance eat into it. Seeing it is like visiting a different planet without leaving Earth. Explore it from the southwest, time it with our best-time guide, and plan with our Madagascar travel guide.

FAQ

What is the spiny forest?

A desert-like ecoregion of southwest Madagascar full of thorny, succulent, drought-adapted plants found almost nowhere else — one of the world’s strangest and most endangered habitats.

What is an octopus tree?

A plant of the endemic Didiereaceae family (such as Didierea madagascariensis) with long, spiny, tentacle-like arms — cactus-like in look but unrelated to cacti.

How unique is the plant life?

Around 95% of the spiny forest’s plant species and nearly half its genera are endemic — the highest plant endemism in Madagascar.

Where is it?

The arid south and southwest, inland from Toliara and the coast.