Parmelia is a genus of medium to large foliose lichens. It has a global distribution, extending from the Arctic to the Antarctic continent but concentrated in temperate regions. There are about 40 species in Parmelia. In recent decades, the once large genus Parmelia has been divided into a number of smaller genera according to thallus morphology and phylogenetic relatedness. It is a foliaceous lichen, resembling a leaf in shape. The ends of the leaf-like lobes are often squarish-tipped. The upper surface is pale bluish-gray to light brown in direct sunlight, with a network web-like ridges and depressions. The lower surface is black and has rhizines anchoring it to the substrate. In general, Parmelia have a dark lower side with rhizines ('rootlets') that attach the lichen to its substrate. The upper side may be several colours - grey, yellow, brown - and may have reproductive organs on it. These may be apothecia (ascospore-producing bodies), isidia or soralia (both vegetative structures). In between these two layers is the medulla, which contains the algal component of the lichen. Taxonomy Parmelia was circumscribed by Swedish lichenologist Erik Acharius in 1803. His idea of the genus, which included foliose species with lecanorine apothecia, was quite broad and included species that are now dispersed in many different genera and families, such as the Peltigeraceae (Lobaria), the Pannariaceae (Pannaria, Parmeliella), the Physciaceae (Physcia, Heterodermia, Physconia), the Teloschistaceae (Xanthoria), as well as the Parmeliaceae (Cetraria, Hypogymnia, and Parmeliopsis). Its broad circumscription meant that almost every lichen with a thalline apothecial rim was included by 19th-century authors. In an attempt to create more homogeneous groups of taxa, lichenologists created new segregate genera for species once in Parmelia. These included Menegazzia (1854), Parmotrema (1860), Anzia (1861), Parmeliopsis (1869), Hypogymnia (1896), Pseudevernia (1903), Pannoparmelia (1912), and Pseudoparmelia (1914). In the 1970s and 1980s, electron microscopy was used to help divide several Parmelia species groups into different genera based on the structure of their cortex. These include Arctoparmelia, Bulbothrix, Canoparmelia, Cetrariastrum, Concamerella, Everniastrum, Flavoparmelia, Hypotrachyna, Neofuscelia, Paraparmelia, Parmelina, Parmotrema, Pseudoparmelia, Relicina, Relicinopsis, Xanthomaculina, and Xanthoparmelia. Another group of species was segregated on the basis of the presence of pseudocyphellae: Punctelia, Flavopunctelia, and Melanelia. In Mason Hale's 1987 monograph on Parmelia, he commented: "The group has been further subdivided ... now leaving in Parmelia a small, apparently irreducible assemblage of species typified by P. saxatilis". In 2016, however, sixteen mostly Australasian species were