The manipulation of any large data set such as this, which is a compilation of many other lists, is fraught with difficulty and requires careful interpretation. In particular the many differences of opinion as to what constitutes a species, subspecies, or variety in the plant kingdom make it difficult to decide which unit is most appropriate to present in summary tables.

Given the data included in the list, three options for providing summary counts are available. The first is to provide counts for all taxa listed (taxa count). This will provide a slight overestimate since some taxa are listed at both the specific and infraspecific level. The second option is to count only taxa listed at the specific level (species count-low), which will provide an underestimate, as some taxa are only listed at the infraspecific level, and information was not available to assess the species as a whole. The third and middle option (species count) is to count as threatened all those taxa listed as threatened at the species level, plus all those species of which at least one component part (ie subspecies or variety) is listed as threatened. The results of the three different methods of counting are summarised in the Table below.

Comparison of potential methods of counting threatened plants

	Ex	Ex/E	E	V	R	I	Total (threatened and extinct)	% decrease from taxa count	% world flora threatened 1
Taxa count	396	400	6,951	8,387	14,998	4,187	35,319	-	13.1%
Species count 2	380	371	6,522	7,951	14,504	4,070	33,798	4.3	12.5%
Species count - low	368	348	6,100	7,309	13,276	3,794	31,195	11.7	11.5%

¹ Calculated against a world flora of 270,000
² The figures used in geographical and taxonomic analyses below

The difference between the highest and lowest estimates for total figures is 11.7%. Even the 'best' case scenario indicates that at least 11.5% (31,195 out of an estimated 270,000 species) of the world's vascular flora is under threat. However it must be recognised that irrespective of the figures used, the situation in reality is much worse due to the major gaps of knowledge about plants, from different regions or taxonomic groups, as well as a conservation point of view. This is particularly accentuated in the tropics.