Caesalpinia decapetala (CAESALPINIACEAE) Mysore Thorn

Weeds to Whack

Originating in India, Mysore Thorn Caesalpinia decapetala is an invasive weed throughout Australia, the Pacific Islands, Asia, the Indian Ocean and parts of Africa. A small specimen was found at Walton Bridge Reserve in 2023. This is a nasty weed to watch out for in Enoggera Catchment.

It is a robust, thorny, evergreen shrub 2–4 m high or climber up to 10 m or higher; often forming dense thickets; the stems are covered with minute golden hair; the stem thorns are straight to hooked, numerous, and not in regular rows or confined to nodes. The leaves are dark green, paler beneath, not glossy, up to 300 mm long; leaflets up to 8 mm wide. The flowers are pale yellow, in elongated, erect clusters 100–400 mm long. Fruit are brown, woody pods, flattened, unsegmented, smooth, sharply beaked at apex, about 80 mm long.

Mysore Thorn is in the same subfamily Caesalpinioideae as Easter Cassia Senna pendula. The leaves are similar to Easter Cassia but the thorny stems make it easy to spot the difference. Mysore Thorn is in the same genus as another local weed the Leopard Tree Caesalpinia ferrea. The genus is named after the botanist Andrea Cesalpino.

Brisbane City Council warns that is an extremely aggressive climbing plant that smothers native vegetation and makes walking though infested areas impossible. It forms stands along roadsides and creeks and invades disturbed tropical and sub-tropical rainforests. This species dominates native vegetation and severely impacts biodiversity through restricting germination, reducing forest biomass and by smothering native species. It also restricts the movement of native fauna and the sprawling thickets provide habitat for foxes and other pest animals.

In Hawai‘i, it forms impenetrable brambles, climbs high up trees, closes off pastures to animals and impedes forest pathways. Trailing branches root where they touch the ground.

Check the Brisbane City Council Weed Identification Tool for more photos of Mysore Thorn Caesalpinia decapetala including flowers and seed pods. Control methods include cut stump and foliar spray.

Prickly stem of Mysore Thorn Caesalpinia decapetala. PHOTO: Anne Jones

Mysore Thorn Caesalpinia decapetala. PHOTO: Anne Jones