The Parmeliaceae is a large and diverse family of

Lecanoromycetes Lecanoromycetes is the largest class of lichenized fungi. It belongs to the subphylum Pezizomycotina in the phylum Ascomycota. The asci (spore-bearing cells) of the Lecanoromycetes most often release spores by rostrate dehiscence. Genera of unc ...

. With over 2700

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

in 71

genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...

, it is the largest family of

lichen A lichen ( , ) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...

. The most speciose genera in the family are the well-known groups: ''

Xanthoparmelia ''Xanthoparmelia'' (commonly known as green rock shields or rock-shield lichens) is a genus of foliose lichen in the family Parmeliaceae.Field Guide to California Lichens, Stephen Sharnoff, Yale University Press, 2014, ''Xanthoparmelia'' is syn ...

'' ( 822 species), ''

Usnea ''Usnea'' is a genus of mostly pale grayish-green fruticose lichens that grow like leafless mini-shrubs or tassels anchored on bark or twigs.Field Guide to California Lichens, Stephen Sharnoff, Yale University Press, 2014, The genus is in the f ...

'' (355 species), ''

Parmotrema ''Parmotrema'' is a genus of lichen belonging to the family Parmeliaceae. It is a large genus, containing an estimated 300 species, with a centre of diversity in subtropical regions of South America and the Pacific Islands. Members of the genus ...

'' ( 255 species), and ''

Hypotrachyna ''Hypotrachyna'' is a genus of lichenized fungi within the family Parmeliaceae The Parmeliaceae is a large and diverse family of Lecanoromycetes. With over 2700 species in 71 genera, it is the largest family of lichen-forming fungi. The m ...

'' (262 species). Nearly all members of the family have a

symbiotic Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...

association with a

green alga The green algae (singular: green alga) are a group consisting of the Prasinodermophyta and its unnamed sister which contains the Chlorophyta and Charophyta/Streptophyta. The land plants (Embryophytes) have emerged deep in the Charophyte alga as ...

(most often ''

Trebouxia ''Trebouxia'' is a unicellular green alga.Silverside, A. J. (2009). Retrieved from http://www.bioref.lastdragon.org/Chlorophyta/''Trebouxia''.html It is a photosynthetic organism that can exist in almost all habitats found in polar, tropical, and ...

'' spp., but '' Asterochloris'' spp. are known to associate with some species).Miadlikowska, J. ''et al.'' (2006). New insights into classification and evolution of the Lecanoromycetes (Pezizomycotina, Ascomycota) from phylogenetic analyses of three ribosomal RNA- and two protein-coding genes. ''Mycologia'' 98: 1088-1103. http://www.mycologia.org/cgi/reprint/98/6/1088.pdf The majority of Parmeliaceae species have a foliose,

fruticose A fruticose lichen is a form of lichen fungi that is characterized by a coral-like shrubby or bushy growth structure. It is formed from a symbiotic relationship of a photobiont such as green algae or less commonly cyanobacteria and one, two or mor ...

, or subfruticose growth form. The morphological diversity and complexity exhibited by this group is enormous, and many specimens are exceedingly difficult to identify down to the species level. The family has a

cosmopolitan distribution In biogeography, cosmopolitan distribution is the term for the range of a taxon that extends across all or most of the world in appropriate habitats. Such a taxon, usually a species, is said to exhibit cosmopolitanism or cosmopolitism. The ext ...

, and is present in a wide range of

habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...

s and climatic regions. This includes everywhere from roadside pavement to alpine rocks, from tropical rainforest trees to subshrubs in the Arctic tundra. Members of the Parmeliaceae are found in most terrestrial environments. Several Parmeliaceae species have been assessed for the global

IUCN Red List The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is the world's most comprehensive inventory of the global conservation status of biol ...

Taxonomy

Based on several molecular

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

studies, the Parmeliaceae as currently circumscribed has been shown to be a

monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...

group. This circumscription is inclusive of the previously described families Alectoriaceae, Anziaceae, Hypogymniaceae, and Usneaceae, which are all no longer recognised by most lichen

systematists Biological systematics is the study of the diversification of living forms, both past and present, and the relationships among living things through time. Relationships are visualized as evolutionary trees (synonyms: cladograms, phylogenetic tr ...

. However, despite the family being one of the most thoroughly studied groups of lichens, several relationships within the family still remain unclear.

Phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

analysis supports the existence of seven distinct

clades A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, t ...

in the family. The Parmelioid clade is the largest, containing 27 genera and about 1850 species – about two-thirds of the species in the family. *Alectorioid clade (5 genera) *Cetrarioid clade (17 genera) *Hypogymnioid clade (4 genera) *Letharioid clade (2 genera) *Parmelioid clade (27 genera) *Psiloparmelioid clade (2 genera) *Usneoid clade (1 genus) Many Parmeliaceae genera do not group phylogenetically into any of these clades, and these, along with genera that have not yet had their DNA studied, are classed as "genera with uncertain affinities". The Parmeliaceae has been divided into two subfamilies, Protoparmelioideae and Parmelioideae. The

diversification Diversification may refer to: Biology and agriculture * Genetic divergence, emergence of subpopulations that have accumulated independent genetic changes * Agricultural diversification involves the re-allocation of some of a farm's resources to n ...

of various Parmelioideae lineages may have been a result of gaining innovations that provided adaptive advantages, such as

melanin Melanin (; from el, μέλας, melas, black, dark) is a broad term for a group of natural pigments found in most organisms. Eumelanin is produced through a multistage chemical process known as melanogenesis, where the oxidation of the amino ...

production in the genus '' Melanohalea''. Diversification of the Protoparmelioideae occurred during the

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...

. The Parmelioid clade is the largest in the Parmeliaceae, with more than 1800 species and a centre of distribution in the Southern Hemisphere.

Evolutionary history

Although fossil records of extant lichen species are scarce, the existence of some

amber Amber is fossilized tree resin that has been appreciated for its color and natural beauty since Neolithic times. Much valued from antiquity to the present as a gemstone, amber is made into a variety of decorative objects."Amber" (2004). In Ma ...

inclusions has allowed for a rough estimate of the

divergence In vector calculus, divergence is a vector operator that operates on a vector field, producing a scalar field giving the quantity of the vector field's source at each point. More technically, the divergence represents the volume density of the ...

of the Parmeliaceae from its most recent common ancestor. An '' Anzia'' inclusion from 35–40

Myr The abbreviation Myr, "million years", is a unit of a quantity of (i.e. ) years, or 31.556926 teraseconds. Usage Myr (million years) is in common use in fields such as Earth science and cosmology. Myr is also used with Mya (million years ago). ...

-old

Baltic amber The Baltic region is home to the largest known deposit of amber, called Baltic amber or succinite. It was produced sometime during the Eocene epoch, but exactly when is controversial. It has been estimated that these forests created more than 1 ...

and '' Parmelia'' from 15–45 Myr-old

Dominican amber Dominican amber is amber from the Dominican Republic derived from resin of the extinct tree ''Hymenaea protera''. Dominican amber differentiates itself from Baltic amber by being nearly always transparent, and it has a higher number of fossil incl ...

suggest a minimum age estimate for the Parmeliaceae of about 40 Myr. A fossil-calibrated phylogeny has estimated the Parmeliaceae to have diversified much earlier, around the

Cretaceous–Paleogene boundary The Cretaceous–Paleogene (K–Pg) boundary, formerly known as the Cretaceous–Tertiary (K–T) boundary, is a geological signature, usually a thin band of rock containing much more iridium than other bands. The K–Pg boundary marks the end of ...

, 58–74 Myr ago.

Characteristics

Thallus

Parmeliaceae thalli are most often foliose, fruticose or subfruticose, but can be umblicate, peltate, caespitose, crustose, or subcrustose. Two genera, '' Nesolechia'' and ''

Raesaenenia ''Raesaenenia'' is a fungal genus in the large family Parmeliaceae. It is a monotypic genus, containing the single lichenicolous fungus ''Raesaenenia huuskonenii'', which parasitises lichens of genus ''Bryoria'' in the Northern Hemisphere. Tax ...

'', contain

lichenicolous fungi A lichenicolous fungus is a parasitic fungus that only lives on lichen as the host. A lichenicolous fungus is not the same as the fungus that is the component of the lichen, which is known as a lichenized fungus. They are most commonly specific to ...

. They can be a variety of colours, from whitish to grey, green to yellow, or brown to blackish (or any combination therein). Many genera are lobe forming, and nearly all are heteromerous (which are

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