Counting complete? Finalising the plant inventory of a global biodiversity hotspot

The Cape Floristic Region – the world’s smallest, but third richest hotspot – experienced sustained levels of taxonomic effort and exploration for almost three centuries resulting in a near-complete plant species inventory. Here we analyse, for a core component of this flora, trends over a 250 year period in taxonomic effort and species discovery linked to ecological and conservation attributes. We show that >40% of species were described within the initial 100 years, followed by a steady rate of description, culminating in <1% of the flora estimated still to be described. A relatively constant cohort of taxonomists working at their ‘taxonomic maximum’ was seen across 250 years, while rates of description remained independent of plant growth-form. Since 1950, narrow-range taxa constituted significantly greater proportions of species discoveries, highlighting the fraction of undiscovered species which exist as localised endemics and thus of high conservation value. In the context of initiated global strategic plans for biodiversity, our dataset provides real world insights for other hotspots to consider the effort required for attaining set targets of comprehensive plant inventories.