A reassessment of 'Boronia' (Rutaceae) in the Northern Territory with a key to species, the description of one new species and the reduction, in synonymy, of another species.

'Boronia' (Rutaceae) is reassessed for the Northern Territory of Australia. Three informal names, 'B. aff. laxa 1' (Northern Plateau, Arnhem Land), 'B. aff. laxa 2' (Nabarlek, Arnhem Land) and 'B. aff. prolixa 1' (Red Lily Lagoon, Arnhem Land), are re-evaluated in the light of the significant number of new collections made over the previous decade. Of the three, only one, 'B. aff. laxa 2' (Nabarlek,Arnhem Land), is considered to be worthy of formal taxonomic recognition and is here newly described as 'B. zeteticorum'' Duretto. The remaining two informal taxa are conspecific with 'B. laxa' Duretto. Additional collections of 'B. gravicocca' Duretto have shown that the taxonomic boundary between it and 'B. filicifolia' A.Cunn. ex Benth. is not clear and thus 'B. gravicocca' is synonymised under 'B. filicifolia'. 'Boronia filicifolia' was previously considered to be endemic to the Kimberley region of Western Australia. High levels of endemism of Boronia in the Northern Territory are discussed. The north-west portion of the Arnhem Land Plateau is determined to be a centre of diversity and endemism for the genus in the Territory and so is an area of high conservation value. A key to the species and subspecies of 'Boronia' found in the Northern Territory is provided.