Diplopanax cacaoides was an early Eocene mastixioid plant that produced a large, very thick-walled one-seeded fruit stone. The robust endocarp formed a substantial protective case around the seed, with a long germination valve and a curved internal seed cavity. No attached vegetative organs are known from these fruits, so the whole plant should not be reconstructed from them alone.

The London Clay material is especially important because it includes the oldest recognised record of Diplopanax. Some fossils were historically grouped under Mastixia cantiensis, but modern anatomical work showed that this old assemblage contained more than one kind of mastixioid fruit. The accepted identification therefore depends on the fruit’s internal construction rather than the old label.