text: It may sometimes be useful to perform other diagnostic measures in addition to spot tests. For example, some lichen metabolites fluoresce under ultraviolet radiation such that exposing certain parts of the lichen to a UV light source can reveal the presence or absence of those metabolites similarly to spot tests. Examples of lichen substances that give a bright fluorescence in UV are alectoronic, lobaric, and divaricatic acids, and lichexanthone. In some cases, the UV light test can be used to help distinguish between closely related species, such as Cladonia deformis (UV−) and Cladonia sulphurina (UV+, due to presence of squamatic acid). Only long-wavelength UV is useful for observing lichens directly.
  More advanced analytical techniques, such as thin-layer chromatography, high-performance liquid chromatography, and mass spectrometry may also be useful in initially characterising the chemical composition of lichens or when spot tests are unrevealing.