Menegazzia
Encyclopedia
Menegazzia is a genus
of lichen
ized fungi containing roughly 70 currently accepted species
. The group is sometimes referred to as the tree flutes, honeycombed lichens, or hole-punch lichens. The most obvious morphological
feature of the genus is the distinctive perforation
s spread across the upper side of the thallus. This makes the group easy to recognise, even for those not particularly familiar with lichen
identification.
The genus has a sub-cosmopolitan distribution (excluding Antarctica), but is concentrated in Australasia
, Melanesia
, and southern South America
. Most species grow exclusively on trees, but some grow on rocks, moss, and/or soil.
in his own right.
has now been confirmed by several molecular studies. However, the exact position of the genus within the Parmeliaceae remains uncertain. It is currently unplaced within the Parmeliaceae. Previously, the morphologically similar genus Hypogymnia
was thought to be the sister genus to Menegazzia, with some authors even separating these two genera into a family of their own, the Hypogymniaceae. However, no molecular phylogenies to date have supported this grouping.
Currently there are three accepted subgenera within Menegazzia: Dispora, Octospora, and Megamenegazzia. However, the monophyletic nature of these three groups remains unknown.
, lobate, and often rosette
-forming, though many species can also be irregularly spreading. It is heteromerous, that is, it contains an upper cortex
, medulla
, green algal
layer (occupied by Trebouxia
spp.), and lower cortex. The thallus can be loosely or closely attached to the substrate, depending on the species. Lobes are generally hollow and inflated, with perforations throughout the corticate upper surface. Only two species of Menegazzia are known which do not contain perforations (M. eperforata, and an as yet undescribed taxon from Papua New Guinea
). Many species can be sorediate
, but only a few isidiate
. Maculae are often present, especially at the lobe tips. The lower surface is also corticate, naked, and often uniformly attached to the substrate (except in M. inflata). This surface is always blackened, and without rhizines. Internal cavities have walls which are most often white, but in some species they can be pigmented or blackened.
, but more frequently are subpedicellate to pedicellate. The apothecial disc is concave to plane, matt to shining, or even pruinose in some taxa (like with M. dielsii), with a well-developed thalline exciple. Epithecium is pigmented, and occasionally has granular inclusions. The hymenium
is always colourless. Hypothecium is chondroid, and made-up of thick-walled, conglutinated cells. Paraphyses are netted, with apical cells that are sometimes capitate, and often pigmented to some extent. Asci
are 2 or 8-spored.
s are simple, colourless, ellipsoid, thick walled, with a broad range of dimensions: 20-120 × 10-50 µm. Pycnidia
, if present, are produced along the lamina, and minute, immersed, and punctiform with a dark apex. Conidia, if present, are short and bacilliform.
s, depside
s, depsidones, and pigment
s.
) forests of Australasia and South America. Most species appear to be very slow growing, especially in dryer habitats, but more study is needed here.
for the family).
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of lichen
Lichen
Lichens are composite organisms consisting of a symbiotic organism composed of a fungus with a photosynthetic partner , usually either a green alga or cyanobacterium...
ized fungi containing roughly 70 currently accepted species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
. The group is sometimes referred to as the tree flutes, honeycombed lichens, or hole-punch lichens. The most obvious morphological
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
feature of the genus is the distinctive perforation
Perforation
A perforation is a small hole in a thin material or web. There is usually more than one perforation in an organized fashion, where all of the holes are called a perforation...
s spread across the upper side of the thallus. This makes the group easy to recognise, even for those not particularly familiar with lichen
Lichen
Lichens are composite organisms consisting of a symbiotic organism composed of a fungus with a photosynthetic partner , usually either a green alga or cyanobacterium...
identification.
The genus has a sub-cosmopolitan distribution (excluding Antarctica), but is concentrated in Australasia
Australasia
Australasia is a region of Oceania comprising Australia, New Zealand, the island of New Guinea, and neighbouring islands in the Pacific Ocean. The term was coined by Charles de Brosses in Histoire des navigations aux terres australes...
, Melanesia
Melanesia
Melanesia is a subregion of Oceania extending from the western end of the Pacific Ocean to the Arafura Sea, and eastward to Fiji. The region comprises most of the islands immediately north and northeast of Australia...
, and southern South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
. Most species grow exclusively on trees, but some grow on rocks, moss, and/or soil.
Etymology
Menegazzia was described by the Veronese lichenologist Abramo Massalongo in 1854. He named it after his friend Luigi Menegazzi, who was a distinguished naturalistNaturalist
Naturalist may refer to:* Practitioner of natural history* Conservationist* Advocate of naturalism * Naturalist , autobiography-See also:* The American Naturalist, periodical* Naturalism...
in his own right.
Taxonomy
Placement of Menegazzia within the ParmeliaceaeParmeliaceae
The Parmeliaceae is a large and diverse family of Lecanoromycetes. With over 2000 species in roughly 87 genera, it is currently regarded as the largest family of lichen forming fungi...
has now been confirmed by several molecular studies. However, the exact position of the genus within the Parmeliaceae remains uncertain. It is currently unplaced within the Parmeliaceae. Previously, the morphologically similar genus Hypogymnia
Hypogymnia
Hypogymnia is a genus of lichenized fungi within the Parmeliaceae family....
was thought to be the sister genus to Menegazzia, with some authors even separating these two genera into a family of their own, the Hypogymniaceae. However, no molecular phylogenies to date have supported this grouping.
Currently there are three accepted subgenera within Menegazzia: Dispora, Octospora, and Megamenegazzia. However, the monophyletic nature of these three groups remains unknown.
Thallus
The thallus of Menegazzia is its most distinctive feature. It is foliose, dorsiventralDorsiventral
Dorsiventral is a term used to describe an organ which has two surfaces differing from each other in appearance and structure, as an ordinary leaf. In biology, this term also refers to that which extends from a dorsal to a ventral surface....
, lobate, and often rosette
Rosette (botany)
In botany, a rosette is a circular arrangement of leaves, with all the leaves at a single height.Though rosettes usually sit near the soil, their structure is an example of a modified stem.-Function:...
-forming, though many species can also be irregularly spreading. It is heteromerous, that is, it contains an upper cortex
Cortex (anatomy)
In anatomy and zoology the cortex is the outermost layer of an organ. Organs with well-defined cortical layers include kidneys, adrenal glands, ovaries, the thymus, and portions of the brain, including the cerebral cortex, the most well-known of all cortices.The cerebellar cortex is the thin gray...
, medulla
Medulla (lichenology)
The medulla is a horizontal layer within a lichen thallus. It is a loosely arranged layer of interlaced hyphae below the upper cortex and photobiont zone, but above the lower cortex. The medulla generally has a cottony appearance. It is the widest layer of a heteromerous lichen thallus....
, green algal
Green algae
The green algae are the large group of algae from which the embryophytes emerged. As such, they form a paraphyletic group, although the group including both green algae and embryophytes is monophyletic...
layer (occupied by Trebouxia
Trebouxia
In taxonomy, Trebouxia is a genus of algae, specifically of the Microthamniales.-Scientific databases:* * *...
spp.), and lower cortex. The thallus can be loosely or closely attached to the substrate, depending on the species. Lobes are generally hollow and inflated, with perforations throughout the corticate upper surface. Only two species of Menegazzia are known which do not contain perforations (M. eperforata, and an as yet undescribed taxon from Papua New Guinea
Papua New Guinea
Papua New Guinea , officially the Independent State of Papua New Guinea, is a country in Oceania, occupying the eastern half of the island of New Guinea and numerous offshore islands...
). Many species can be sorediate
Soredium
Soredia are common reproductive structures of lichens. Lichens reproduce asexually by employing simple fragmentation and production of soredia and isidia. Soredia are powdery propagules composed of fungal hyphae wrapped around cyanobacteria or green algae. Fungal hyphae make up the basic body...
, but only a few isidiate
Isidium
An isidium is a vegetative reproductive structure present in some lichens. Isidia are outgrowths of the thallus surface, and are corticated , usually with a columnar structure, and consisting of both fungal hyphae and algal cells...
. Maculae are often present, especially at the lobe tips. The lower surface is also corticate, naked, and often uniformly attached to the substrate (except in M. inflata). This surface is always blackened, and without rhizines. Internal cavities have walls which are most often white, but in some species they can be pigmented or blackened.
Apothecia
Rounded apothecia are produced along the lamina of most of the known Menegazzia species, while the others are thought to be entirely asexual (like M. nothofagi and M. globulifera). In the taxa that do produce apothecia, they are always lecanorine, and often cupuliform. They can be sessileSessility (botany)
In botany, sessility is a characteristic of plants whose flowers or leaves are borne directly from the stem or peduncle, and thus lack a petiole or pedicel...
, but more frequently are subpedicellate to pedicellate. The apothecial disc is concave to plane, matt to shining, or even pruinose in some taxa (like with M. dielsii), with a well-developed thalline exciple. Epithecium is pigmented, and occasionally has granular inclusions. The hymenium
Hymenium
The hymenium is the tissue layer on the hymenophore of a fungal fruiting body where the cells develop into basidia or asci, which produce spores. In some species all of the cells of the hymenium develop into basidia or asci, while in others some cells develop into sterile cells called cystidia or...
is always colourless. Hypothecium is chondroid, and made-up of thick-walled, conglutinated cells. Paraphyses are netted, with apical cells that are sometimes capitate, and often pigmented to some extent. Asci
Ascus
An ascus is the sexual spore-bearing cell produced in ascomycete fungi. On average, asci normally contain eight ascospores, produced by a meiotic cell division followed, in most species, by a mitotic cell division. However, asci in some genera or species can number one , two, four, or multiples...
are 2 or 8-spored.
Spores
The ascosporeAscospore
An ascospore is a spore contained in an ascus or that was produced inside an ascus. This kind of spore is specific to fungi classified as ascomycetes ....
s are simple, colourless, ellipsoid, thick walled, with a broad range of dimensions: 20-120 × 10-50 µm. Pycnidia
Pycnidium
A pycnidium is an asexual fruiting body produced by mitosporic fungi in the form order Sphaeropsidales . It is often spherical or inversely pearshaped and its internal cavity is lined with conidiophores. When ripe, an opening generally appears at the top, through which the pycnidiospores escape....
, if present, are produced along the lamina, and minute, immersed, and punctiform with a dark apex. Conidia, if present, are short and bacilliform.
Chemistry
Members of the genus have a diverse chemistry, including fatty acidFatty acid
In chemistry, especially biochemistry, a fatty acid is a carboxylic acid with a long unbranched aliphatic tail , which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from...
s, depside
Depside
A depside is a type of polyphenolic compound composed of two or more monocyclic aromatic units linked by an ester bond. Depsides are most often found in lichens, but have also been isolated from higher plants, including species of the Ericaceae, Lamiaceae, Papaveraceae and Myrtaceae. Depsides have...
s, depsidones, and pigment
Pigment
A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...
s.
Ecology
Menegazzia species are most often corticolous, but several species are saxicolous, muscicolous, and/or terricolous. This group tends to be most abundant and diverse in the southern beech (NothofagusNothofagus
Nothofagus, also known as the southern beeches, is a genus of 35 species of trees and shrubs native to the temperate oceanic to tropical Southern Hemisphere in southern South America and Australasia...
) forests of Australasia and South America. Most species appear to be very slow growing, especially in dryer habitats, but more study is needed here.
Evolution
Ascus evolution in Menegazzia is of particular interest, because many species have 2-spores per ascus, while all nearly other genera in the Parmeliaceae have 8-spores (making the character likely plesiomorphicCladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...
for the family).
Uses
Menegazzia does not produce any economically important products, nor is it known to have had any uses by indigenous peoples. However, the genus is important for some small insects, which use the hollow lobes for shelter and the upper cortex for food.External links
- Menegazzia at the online Flora of New Zealand - Lichens - Revised 2nd Edition (2007)
- Menegazzia at the online Flora of New Zealand - Lichens (1985)
- Menegazzia at the online Checklist of the Lichens Of Australia and its Island Territories (2010)
- Menegazzia at the online Encyclopedia of Life
- Menegazzia gallery at Pictures of Tropical Lichens Online