There are several spot tests that are infrequently used due to their limited applicability, but may be useful in situations where particular lichen metabolites need to be detected, or to distinguish between certain species when other tests are negative.
* A 10% solution of barium hydroxide (Ba(OH)) gives a violet colour when tested with diploschistesic acid, a chemical found in some Diploschistes species.
* A saturated solution of barium peroxide (BaO), when tested with olivetoric acid, will turn a yellow colour that becomes green after a few minutes.
* A 1% (weight per volume) solution of ferric chloride (FeCl) in ethanol produces several possible colours when tested with compounds that have phenolic groups.
* The N test uses a 35% solution of nitric acid, which can be used to distinguish species of Melanelia from brown species of Xanthoparmelia.
* The S test uses a sulphuric acid solution (0.5% to 10%) brushed over an acetone-extracted, dried sample from a lichen thallus, followed by heating over a flame for 30 seconds or until colour develops. A persistent violet to bright pink colour indicates the presence of miriquidic acid and can be used to distinguish between the two morphologically similar snow lichens, Stereocaulon alpinum and S. groenlandicum without having to resort to more laborious chemical analysis.
*The Beilstein test involves heating a small sample of the substance to be tested on a copper wire; halogenated compounds cause a temporary deep green flame colour.