Mellissia was formerly a monotypic genus in the family Solanaceae with the single species, Mellissia begoniifolia (Saint Helena boxwood), endemic to the island of Saint Helena.

It was named by Joseph Dalton Hooker in honour of John Charles Melliss, a 19th-century engineer and amateur naturalist who worked on Saint Helena.

The plant formerly known as Mellissia begoniifolia is notable for the subcampanulate calyx which encloses the white corolla, and is strongly accrescent in fruit, as in certain species of Physalis e.g. Physalis philadelphica.

The plant was long thought to be extinct but a small population was discovered in 1998 by Stedson Stroud.

Only one adult plant was left by 2010, and it was under extreme stress due to drought and pests.