Madagascar spiny thickets, WWF ecoregion in southern Madagascar.

The Madagascar spiny thickets cover southern arid regions with scattered, thorny trees and thick shrubs adapted to dry conditions. These dense plant communities feature species with swollen trunks and reduced leaves as water-storage adaptations.

The ecoregion lies in southwestern Madagascar, bounded to the north by the Mangoky River and the Anosy mountain ridge, and covers about 44,300 km² of the southern and southwestern coastal strip. WWF defines it as an ecoregion of the Afrotropical realm, grouped with the Madagascar succulent thicket as the Global 200 'Madagascar thickets'. Its Didiereoideae are woody plants only distantly related to cacti.

Residents use the wood of Alluaudia procera, a dominant tree of the thickets, for construction, and its thorny stems for fencing and security. Lemurs and other wildlife regularly feed on its fleshy leaves. The ecoregion's name comes from the spiny Didiereoideae that define it.

Only 8.31% of the ecoregion lies in protected areas, among them Tsimanampetsotsa National Park, Berenty and Beza Mahafaly reserves and Cap Sainte Marie Special Reserve; Andohahela protects a section through its Parcel Three. The Arboretum d'Antsokay near Toliara is a botanical garden devoted to the spiny forest flora. Elsewhere the habitat is under pressure from burning for farmland and pasture, charcoal and firewood harvesting, and logging for construction.

Some trees here store water in thickened trunks and have transformed leaves into thorns to reduce water loss. These extreme adaptations allow plants to survive the long dry periods common in this harsh region.