Background and aims – The genus Idertia belongs to the subfamily Ochnoideae, tribe Ochneae, subtribe Ouratinae. This paper aims at a full taxonomic revision and a critical evaluation of the taxonomic position of the genus along with its diagnostic characters. Methods – All characters are studied using 73 herbarium collections of the following herbaria: B, BM, BR, BRLU, COI, EA, G, K, MO, P and WAG. Specimen data were managed using the BRAHMS herbarium management software. Key results – Idertia is characterized by a gynobasic style, apocarpous fruits, ten stamens, persistent and accrescent sepals and intra-axillary fused stipules. It shares these features with its African relatives Campylospermum and Rhabdophyllum, but its axillary inflorescence, smooth anthers and straight cotyledons renders it distinct. The latter feature is reminiscent of the South American relative Ouratea which lacks the persistent sepals and has free lateral stipules. Other diagnostic characters of the wood, leaves, inflorescence, flowers and fruits are discussed. A key to the four genera of the subtribe Ouratinae is provided. The correct author combination for the name Ouratinae is (Engl.) Kanis. The variation amongst the four species of Idertia recognized by other authors was studied carefully and deemed continuous. Only a single, though variable species distributed from Guinea to Uganda is recognized. A full taxonomic treatment is provided and two lectotypes are designated. Conclusions – Idertia is a well-defined and sufficiently distinct monotypic genus.

TAXONOMY; AFRICA; MORPHOLOGY; CAMPYLOSPERMUM; IDERTIA; LECTOTYPE; OCHNACEAE; OCHNOIDEAE; OURATEA; OURATINAE; RHABDOPHYLLUM