This paper aims to throw light on the mass extinction that is overtaking Earth's species. Using an analytic methodology developed for an earlier partial assessment, it focuses on a series of "hotspot" areas, these being areas that a) feature exceptional concentrations of species with high levels of endemism and b) face exceptional threats of destruction. The paper identifies another 8 such areas, 4 of them in tropical forests and 4 in Mediterranean-type zones. The analysis reveals that the 4 tropical-forest areas contain at least 2835 endemic plant species in 18,700 sq. km, or 1.1% of Earth's plant species in 0.013% of Earth's land surface; and that the 4 Mediterranean-type areas contain 12,720 endemic plant species in 435,700 sq. km, or 5.1% of Earth's plant species in 0.3% of the Earth's land surface. Taken together, these 8 hotspot areas contain 15,555 endemic plant species in 454,400 sq. km, or 6.2% of Earth's plant species in 0.3% of Earth's land surface. This is to be compared with the earlier hotspot analysis of 10 tropical-forest areas, with 34,400 endemic plant species in 292,00 sq. km, or 13.8% of Earth's plant species in 0.2% of Earth's land surface. Taking all 18 hot-spot areas together, the authors find they support 49,995 endemic plant species, or 20% of Earth's plant species, in 746,400 sq. km, or 0.5% of Earth's land surface. This means that one-fifth of Earth's plant species are confined to 0.5% of the Earth's land surface--and they occur in habitats that are mostly threatened with imminent destruction. By concentrating on these hotspot areas where needs are greatest and where the pay-off from safeguard measures would be greatest, conservationists can engage in a more systematized response to the challenge of large-scale impending extinctions.