The Parmeliaceae is a large and

diverse Diversity, diversify, or diverse may refer to: Business *Diversity (business), the inclusion of people of different identities (ethnicity, gender, age) in the workforce * Diversity marketing, marketing communication targeting diverse customers ...

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. The group is ...

. With over 2700

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

in 71

genera Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...

, it is the largest family of

lichen A lichen ( , ) is a hybrid colony (biology), colony of algae or cyanobacteria living symbiotically among hypha, filaments of multiple fungus species, along with yeasts and bacteria embedded in the cortex or "skin", in a mutualism (biology), m ...

-forming

fungi A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...

. 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 lichens in the family Parmeliaceae.Field Guide to California Lichens, Stephen Sharnoff, Yale University Press, 2014, This genus of lichen i ...

'' ( 822 species), ''

Usnea ''Usnea'' is a genus of fruticose lichens in the large family Parmeliaceae. The genus, which currently contains roughly 130 species, was established by Michel Adanson in 1763. Species in the genus grow like leafless mini-shrubs or tassels anch ...

'' (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. According to the ''Dictionary of the Fungi'' (10th edition, 2008), the widespread genus contains about 198 species. ''Hypotrachyna'' was circumscribed by American lic ...

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

symbiotic Symbiosis (Ancient Greek : living with, companionship < : together; and ''bíōsis'': living) is any type of a close and long-term biolo ...

association with a

green alga The green algae (: green alga) are a group of chlorophyll-containing autotrophic eukaryotes consisting of the phylum Prasinodermophyta and its unnamed sister group that contains the Chlorophyta and Charophyta/ Streptophyta. The land plants ( ...

(most often ''

Trebouxia ''Trebouxia'' is a unicellular green alga. It is a photosynthetic organism that can exist in almost all habitats found in polar, tropical, and temperate regions.Erokhina, L. G., Shatilovich, A. V., Kaminskaya, O. P., & Gilichinskii, D. A. (2004 ...

'' spp., but ''

Asterochloris ''Asterochloris'' is a genus of green algae in the family Trebouxiophyceae. It is a common in lichen, occurring in the thalli of more than 20 lichen genera worldwide. ''Asterochloris'' is distinguishable from the morphologically similar genus ...

'' 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 A foliose lichen is a lichen with flat, leaf-like , which are generally not firmly bonded to the substrate on which it grows. It is one of the three most common lichen growth forms, growth forms of lichens. It typically has distinct upper and lo ...

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

, 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, a cosmopolitan distribution is the range of a taxon that extends across most or all of the surface of the Earth, in appropriate habitats; most cosmopolitan species are known to be highly adaptable to a range of climatic and en ...

, and is present in a wide range of

habitat In ecology, habitat refers to the array of resources, 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 manifestation of its ...

s and

climatic regions Climate is the long-term weather pattern in a region, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteorolog ...

. This includes everywhere from roadside pavement to alpine rocks, from tropical rainforest trees to subshrubs in the

Arctic tundra In physical geography, a tundra () is a type of biome where tree growth is hindered by frigid temperatures and short growing seasons. There are three regions and associated types of tundra: Arctic, Alpine, and Antarctic. Tundra vegetation is ...

. Members of the Parmeliaceae are found in most

terrestrial Terrestrial refers to things related to land or the planet Earth, as opposed to extraterrestrial. Terrestrial may also refer to: * Terrestrial animal, an animal that lives on land opposed to living in water, or sometimes an animal that lives on o ...

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 an inventory of the global conservation status and extinction risk of biological ...

Taxonomy

Based on several molecular

phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

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

monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

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. 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 () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

analysis supports the existence of seven distinct

clades In biology, a clade (), also known as a monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach to taxonomy ...

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) An early molecular phylogenetic study in 1998 using nuclear ribosomal DNA sequences challenged some of the morphology-based classifications, particularly finding a close relationship between '' Cetraria'' and '' Vulpicida'' that contradicted previous assumptions based on ascus structure differences. 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 of various Parmelioideae lineages may have been a result of gaining innovations that provided adaptive advantages, such as

melanin Melanin (; ) is a family of biomolecules organized as oligomers or polymers, which among other functions provide the pigments of many organisms. Melanin pigments are produced in a specialized group of cells known as melanocytes. There are ...

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

Miocene The Miocene ( ) is the first epoch (geology), 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 mea ...

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

Generic classification

The classification history of Parmeliaceae reflects evolving approaches to fungal taxonomy over two centuries. When

Erik Acharius Erik Acharius (10 October 1757 – 14 August 1819) was a Swedish botanist who pioneered the Taxonomy (biology), taxonomy of lichens and is known as the "father of lichenology". Acharius was famously the last pupil of Carl Linnaeus. Life Ac ...

first described ''Parmelia'' in 1803, it encompassed a broad range of foliose lichens with rounded apothecia. By the mid-1800s, researchers began segregating genera based on

ascospore In fungi, an ascospore is the sexual spore formed inside an ascus—the sac-like cell that defines the division Ascomycota, the largest and most diverse Division (botany), division of fungi. After two parental cell nucleus, nuclei fuse, the ascu ...

characteristics, leading to the recognition of distinct groups like ''Physcia'' and ''Xanthoria''. The most dramatic period of generic splitting occurred in the 1970s and 1980s, when

Mason Hale Mason Ellsworth Hale, Jr. (September 23, 1929 – April 23, 1990) was one of the most prolific American lichenologists of the 20th century. Many of his scholarly articles focused on the taxonomy of the family Parmeliaceae. Hale was one of the fi ...

and others proposed numerous new genera based primarily on morphological features such as shapes,

rhizine In lichens, rhizines are multicellular root-like structures arising mainly from the lower surface. A lichen with rhizines is termed rhizinate, while a lichen lacking rhizines is termed erhizinate. Rhizines serve only to anchor the lichen to their s ...

types, and cortical chemistry. The advent of

molecular phylogenetics Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...

techniques in the late 1990s provided new tools for evaluating which morphological and chemical characters were most reliable for defining genera. These studies led to significant refinements in generic concepts, supporting some previously proposed splits while showing others to be artificial. For example, molecular data revealed that the brown-fruited genus ''Neofuscelia'' needed to be merged into ''

'', while confirming that groups like ''

'' and '' Cetrelia'' represented distinct evolutionary lineages. Current understanding of generic relationships in Parmeliaceae emphasises the importance of reproductive characters over vegetative features. Characters of the ascomata (especially anatomy and characteristics),

conidia A conidium ( ; : conidia), sometimes termed an asexual chlamydospore or chlamydoconidium (: chlamydoconidia), is an asexual, non- motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are also ...

l types, and

cell wall A cell wall is a structural layer that surrounds some Cell type, cell types, found immediately outside the cell membrane. It can be tough, flexible, and sometimes rigid. Primarily, it provides the cell with structural support, shape, protection, ...

polysaccharide Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long-chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with wat ...

s have proven particularly valuable for defining natural groups. In contrast, some previously emphasised features such as thallus

growth form Plant life-form schemes constitute a way of classifying plants alternatively to the ordinary species-genus-family scientific classification. In colloquial speech, plants may be classified as trees, shrubs, herbs (forbs and graminoids), etc. The sci ...

and the presence of specific cortical substances have been shown to be more variable within lineages than previously thought. Modern molecular studies have established that approximately 75% of Parmeliaceae species belong to well-defined major

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

s, including groups like ''Xanthoparmelia'', ''

'', and their close relatives. The relationships among the remaining genera continue to be refined through ongoing research. Rather than being defined by single diagnostic features, most genera are now recognised as

groups characterised by unique combinations of multiple morphological, chemical, and anatomical traits.

Evolutionary history

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

amber Amber is fossilized tree resin. Examples of it have been appreciated for its color and natural beauty since the Neolithic times, and worked as a gemstone since antiquity."Amber" (2004). In Maxine N. Lurie and Marc Mappen (eds.) ''Encyclopedia ...

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 rate that the vector field alters the volume in an infinitesimal neighborhood of each point. (In 2D this "volume" refers to ...

of the Parmeliaceae from its

most recent common ancestor A most recent common ancestor (MRCA), also known as a last common ancestor (LCA), is the most recent individual from which all organisms of a set are inferred to have descended. The most recent common ancestor of a higher taxon is generally assu ...

. An '' Anzia'' inclusion from 35–40

Myr Million years ago, abbreviated as Mya, Myr (megayear) or Ma (megaannum), is a unit of time equal to (i.e. years), or approximately 31.6 teraseconds. Usage Myr is in common use in fields such as Earth science and cosmology. Myr is also used w ...

-old

Baltic amber Baltic amber or succinite is amber from the Baltic region, home of its largest known deposits. It was produced sometime during the Eocene epoch, but exactly when is controversial. It has been estimated that this forested region provided the re ...

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 in ...

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 o ...

, 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'', contain

lichenicolous fungi A lichenicolous fungus is a member of a specialised group of fungi that live exclusively on lichens as their host (biology), host organisms. These fungi, comprising over 2,000 known species across 280 genera, exhibit a wide range of ecological st ...

. 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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