Genetic distinctiveness supports the resurrection of the South African Juncus acutissimus (Buchenau) Adamson as a subspecies of J. inflexus L.

Juncus acutissimus (Buchenau) Adamson was originally described by Buchenau in 1875 as a variety of J. glaucus Sibth. (now J. inflexus L.) from South Africa and elevated to species rank by Adamson in 1935. Contemporary taxonomic treatments, including Kirschner’s global monograph, currently consider it a synonym of J. inflexus. However, recent findings along the Meuse River in Limburg, the Netherlands – originating from the soil seed bank – have revealed populations of J. acutissimus with a likely historical link to the wool-processing industry upstream along the Vesdre River in Belgium. This industry imported large quantities of raw wool primarily from Australia, South Africa, and South America. Genetic analysis (ITS and trnL-F markers) confirms that these populations are closely related to J. inflexus but exhibit consistent genetic divergence. Based on morphological, genetic, and biogeographical evidence, we propose to recognize Juncus acutissimus as a subspecies of J. inflexus.