Pachypodium horombense is a succulent shrublet about 1.5 m high with a plump, bottle-shaped, main stem surmounted by a number of short, spiny fat arms each bearing a rosette of leaves and a single long-peduncled inflorescence that carries 3-10, broadly cup-shaped, horizontal, gold flowers during the warm months of the year.
The flower has an inflated corolla that forms five large sacs into which the pollinator can crawl. Unless in flower, it's difficult to distinguish it from the cactus pachypodium (Pachypodium rosulatum).