The 83rd plate from Ernst Haeckel’s ”Kunstformen der Natur” (1904), depicting organisms classified as Lichenes and including Cladonia retipora, Cladonia perfoliata, Cladonia verticillata, Cladonia squamosa, Cladonia fimbriata, Cladonia cornucopiae, Sticta pulmonaria, Parmelia stellarias, Parmelia olivacea, Parmelia caperata and Hagenia crinalis (image retrieved from Wikipedia); image modified by MIC. The cover is published under the Creative Commons Attribution (CC BY) license.