Morphological Authentication of Species Defined by Morphology: Can One Speak of Validating Methods and How?

Plant species are defined and distinguished from other species by morphological characters. Proxy methods of identification using molecular or chemical markers should be validated because the distribution of many potential markers is not congruent with taxonomic identity. Validation demonstrates that a method is acceptably likely, for some set of samples, to return positive results for correctly identified material and negative results for unwanted species. This requires access to independent, definitive identifications, which are derived from morphology. Hence, one might presume that morphological identification is inherently valid but cannot be validated, since no other method exists that could supply more definitive, potentially contradictory identifications. However, the usually reliable conventional tools for non-expert botanical identification, such as dichotomous keys, are frequently unusable to identify incomplete material. Written descriptions of commercial botanicals must often omit definitive taxonomic characters and compensate by including anatomical characters whose distribution may not be documented in detail. Such tools are not, therefore, automatically fit for purpose. A given list of characters purported to distinguish correctly identified from unwanted species in commerce might not reliably do so, either because the species are not always distinguishable, or because the list's compiler overlooked useful characters or understated within-species variability. Therefore, these tools could appropriately be tested by having a trained person use them to authenticate blinded samples whose identity is fixed by examination of associated intact voucher specimens.