Zopf specially insists that the grouping of this series must be regarded as only a provisional arrangement of the many lichen-acids that are included therein. All of them are split up into orcine and carbonic acid by ammonia and other alkalies. On exposure to air, the ammoniacal or alkaline solution changes gradually into orceine, the colouring principle and chief constituent of commercial orchil. Orcine is not found free in nature. The orcine subseries includes five groups:
Group 1. The substances in this group form, with hypochlorite of lime (“CaCl”), red-coloured compounds which yield, on splitting, orsellinic acid. Zopf enumerates seven acids as belonging to this group, among which is lecanoric acid (C₁₆H₁₄O₇), found in many different lichens, e.g. Roccella tinctoria, Lecanora tartarea, etc.: whenever there is a differentiated pith and cortex it occurs in the pith alone. Erythrin (C₂₀H₂₂O₁₀), a constituent of the British marine lichen Roccella fuciformis, also belongs to this orsellinic group.
Group 2. Substances which also form red products with CaCl, but do not break up into orsellinic acid. Among the most noteworthy are olivetoric acid (C₂₁H₂₆O₇), a constituent of Evernia furfuracea, perlatic acid (C₂₈H₃₀O₁₀) and glabratic acid (C₂₄H₂₆O₁₁), which are obtained from species of Parmelia.
Group 3. Contains three acids of somewhat restricted occurrence. They do not form red products with CaCl, and they yield on splitting everninic acid. They are: evernic acid (C₁₇H₁₆O₇), found in Evernia prunastri var. vulgaris, ramalic acid (C₁₇H₁₆O₇) in Ramalina pollinaria, and umbilicaric acid (C₂₅H₂₂O₁₁) in species of Gyrophora.
Group 4. The numerous acids of this group are not easily soluble and have a very bitter taste. They are not coloured by CaCl; when extracted with concentrated sulphuric acid, the solution obtained is reddish-yellow or deep red. Among the most frequent are fumarprotocetraric acid (C₆₂H₅₀O₃₅), the bitter principle of Cetraria islandica, Cladonia rangiferina, etc., psoromic acid (C₂₀H₁₄O₉), obtained from Alectoria implexa, Lecanora varia, Cladonia pyxidata and many other lichens, and salazinic acid (C₁₉H₁₄O₁₀), recorded by Zopf as occurring in Stereocaulon salazinum and in several Parmeliae, but now found by Lettau[829] to be very wide-spread. He used micro-chemical methods and detected its presence in 72 species from twelve different families. The distribution of the acid in the thallus varies considerably.
Group 5. This is called the atranorin group from one of the most important members. They are colourless substances and, like the preceding group, are not affected by CaCl, but when split they form bodies that colour a more or less deep red with that reagent. Atranorin (C₁₉H₁₈O₈) is one of the most widely spread of all lichen-acids; it occurs in Lecanoraceae, Parmeliaceae, Physciaceae and Lecideaceae. Barbatinic acid (C₁₉H₂₀O₇), another member, is found in Usnea ceratina, Alectoria ochroleuca and in a variety of Rhizocarpon geographicum. A very large number of acids more or less fully studied belong to this group.
Subseries II. Anthracene Derivatives
The constituents of this subseries are derived from the carbohydrate anthracene, and are characterized by their brilliant colours, yellow, red, brown, red-brown or violet-brown. So far, only ten different kinds have been isolated and studied. Parietin[830] (C₁₆H₁₂O₅), one of the best known, has been extracted from Xanthoria parietina, Placodium murorum and several other bright-yellow lichens; solorinic acid (C₁₅H₁₄O₅) occurs in orange-red crystals on the hyphae of the pith and under surface of Solorina crocea; nephromin (C₁₆H₁₂O₆) is found in the yellow medulla of Nephromium lusitanicum; rhodocladonic acid (C₁₂H₈O₆ or C₁₄H₁₀O₇) is the red substance in the apothecia of the red-fruited Cladoniae.
There are, in addition, a short series of coloured substances which are of uncertain position. They are imperfectly known and are of rare occurrence. An acid containing nitrogen has been extracted from Roccella fuciformis, and named picroroccellin[831] (C₂₇H₂₉N₃O₅). It crystallizes in comparatively large prisms, has an exceedingly bitter taste, and is very sparingly soluble. It is the only lichen-acid in which nitrogen has been detected.
One acid at least, belonging to the Fat series, vulpinic acid, which gives the greenish-yellow colour to Letharia vulpina, has been prepared synthetically by Volkard[832].