Isoglossa woodii, commonly known as buckweed, is a monocarpic shrub of the family Acanthaceae, growing up to 4 m tall.

It grows in colonies in coastal forest areas of KwaZulu-Natal and marginally into Eastern Cape and Free State of South Africa.

These plants form dense colonies in the understorey of forests where they provide food and shelter to many animals.

Buckweed is excluded from areas of forest with dense tree cover and in turn plays a role in limiting forest regeneration as the tree seedling community beneath Isoglossa woodii shows reduced density and species richness from areas where I. woodii is absent.

The common name of buckweed is a reference to these plants being abundant and being browsed by forest antelopes.