Benna alternifolia (Melastomataceae: Sonerileae), a new herbaceous genus and species from Guinea, West Africa

Benna is a new monospecific genus in the Melastomataceae, from the Benna Plateau in Forécariah Prefecture in Guinea, West Africa. Molecular sequence data show the genus Benna is nested within the tribe Sonerileae but clearly unrelated to the other African Sonerileae genera. The genus is weakly supported as sister to the South American Sonerileae genus Phainantha.

Similarities and differences with African and American Sonerileae genera are listed. The new species Benna alternifolia is a perennial evergreen herb, half-spherical in shape, up to 1.2 m in diameter. A plant may have up to 60 alternate leaves, with petioles up to 45 cm long and blades up to 31 × 28 cm.

The flowers are actinomorphic, with 4 sepals and 4 pink petals, 8 dimorphic stamens, and an inferior 4-locular ovary. The fruit is a capsule. The seeds are obovoid or nearly so, with a smooth testa.

Benna alternifolia occurs in deep shade in canyons, on vertical or overhanging sandstone rocks out of reach of falling rain drops, and only where water is seeping all year round, including during the 6-month dry season. About 680 plants were found. Benna alternifolia is assessed to the IUCN category Near Threatened.