Taxonomic classifications simultaneously represent hypotheses of taxon identity and
relationships to taxonomists, and real, unchanging entities to users of taxonomic information.
Taxonomic changes, while representing scientific progress, can be a source of frustration for
users. A method for assessing confidence in the taxonomy of a group of organisms would assist
users of the taxonomy. A method is presented for determining the degree of development of a
taxonomy, a concept termed ‘taxonomic resolution’. The method was applied to six groups of
southern African mygalomorph trapdoor spiders, namely Stasimopus Simon 1892 (Ctenizidae
Thorell 1877), Ancylotrypa Simon 1889 (Cyrtaucheniidae Simon 1889), four genera of Idiopidae
Simon 1889 assessed as a single group, Galeosoma Purcell 1903, the families Migidae Simon
1889 and Microstigmatidae Roewer 1942, and the burrowing scorpion genus Opistophthalmus C.
L. Koch 1837 (Scorpionidae Latreille 1802). The method was based on the assumption that
species delimitation in a group of organisms, the taxonomy of which is based on morphological
characters, depends on whether the sample of material examined is adequate for assessing
variation in those characters. Five assessment criteria were identified and scored for a group of
species using the taxonomic literature. Estimates of the number of species remaining to be
discovered and described in each group were also included in the assessment. The results
obtained for the trapdoor spiders ranged from 15 to 29%, indicating a potentially significant
degree of uncertainty in the taxonomy. Results for Migidae and Microstigmatidae were 51 and
78% respectively, whereas the result for Opistophthalmus was 93%. The applied value of a
measure of taxonomic resolution, the limitations of the method, and a strategy for developing a
more generally applicable method are discussed.