How photographs can be a complement of herbarium vouchers: a proposal of standardization

Challenges in the collection of vouchers, either because of the physical properties of the material (species difficult to collect or to press, e.g., palms, cycads, toxic plants, and cacti) or because drying may have a negative effect on taxonomic characters (e.g., colour), recommend the use of photographs to complement herbarium specimens. In a series of cases (enumerated in the present contribution), however, it may be impossible to collect material and, thus, photographs may be the only option to document the presence of a plant in a given locality. We propose in this paper some guidelines for the standardization of photographs intended for deposit in herbaria