A taxonomic revision of the “Quadrispina clade” of Barleria sect. Prionitis.

The recently recognised Quadrispina clade within Barleria sect. Prionitis Nees (Acanthaceae) represents a taxonomically challenging group endemic to the Horn of Africa biodiversity hotspot. This study presents a comprehensive taxonomic revision of the complex, driven by morphological assessment and morphometric analyses. We recognise seven species in the complex in total, including four new species to science that had previously been included within B. quadrispina, namely B. filtuensis, B. mudugensis, B. puberulifolia and B. sebsebei. In addition, we recognise four subspecies within B. quadrispina, namely subsp. quadrispina, subsp. glaucobracteata, subsp. waggana and the newly described subsp. kenyana. Conservation assessments based on IUCN Red List categories and criteria indicate that B. filtuensis, B. mudugensis, B. puberulifolia, B. sebsebei and B. quadrispina subsp. glaucobraceata are range-restricted and potentially threatened by habitat degradation, hence they are preliminarily assessed as threatened under criterion B, whilst B. quadrispina subsp. kenyana remains Data Deficient.