''Lecanora polytropa'', commonly known as the granite-speck rim lichen, is a species of saxicolous lichen in 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 most speciose genera in the family are the well-known groups: '' Xanthoparmelia'' ( 822 ...

. A small, inconspicuous species that grows in the cracks of rock surfaces, it 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 has been recorded on all continents, including Antarctica.

Taxonomy

It was originally described by German botanist

Jakob Friedrich Ehrhart Jakob Friedrich Ehrhart (4 November 1742, Holderbank, Aargau – 26 June 1795) was a German botanist, a pupil of Carl Linnaeus at Uppsala University, and later director of the Botanical Garden of Hannover, where he produced several major botanical ...

in 1796 as a species of ''

Verrucaria ''Verrucaria'' is a genus of lichenized (lichen-forming) fungi in the family Verrucariaceae. Taxonomy The genus was circumscribed by German botanist Heinrich Adolph Schrader in 1794, with '' Verrucaria rupestris'' assigned as the type species. I ...

''. Gottlob Ludwig Rabenhorst transferred it to the genus ''

Lecanora ''Lecanora'' is a genus of lichen commonly called rim lichens.Field Guide to California Lichens, Stephen Sharnoff, Yale University Press, 2014, Lichens in the genus ''Squamarina'' are also called rim lichens. Members of the genus have roughly ci ...

'' in 1845. It is commonly known as the granite-speck rim lichen.

Description

Lecanora polytropa - Flickr - pellaea (3)

''Lecanora polytropa'' has a scanty

thallus Thallus (plural: thalli), from Latinized Greek (), meaning "a green shoot" or "twig", is the vegetative tissue of some organisms in diverse groups such as algae, fungi, some liverworts, lichens, and the Myxogastria. Many of these organisms wer ...

, which sometimes resembles tiny pale yellowish areoles. The tiny, flat apothecia typically measure 0.3–0.9 mm in diameter and may be scattered or clustered together. They have a waxy texture and are yellow to pale orange, lacking pruina. The margins of the apothecia are smooth, not prominent, and tend to be lighter in colour than the central disc.

Ascospore An ascus (; ) is the sexual spore-bearing cell produced in ascomycete fungi. Each ascus usually contains eight ascospores (or octad), produced by meiosis followed, in most species, by a mitotic cell division. However, asci in some genera or s ...

s are

ellipsoid An ellipsoid is a surface that may be obtained from a sphere by deforming it by means of directional scalings, or more generally, of an affine transformation. An ellipsoid is a quadric surface; that is, a surface that may be defined as the ...

and measure 8–15 by 5–7

μm The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is a unit of length in the International System of Unit ...

Habitat and distribution

''Lecanora polytropa'' grows on

siliceous rock Siliceous rocks are sedimentary rocks that have silica (SiO2) as the principal constituent. The most common siliceous rock is chert; other types include diatomite. They commonly form from silica-secreting organisms such as radiolarians, diatoms, or ...

, particularly

granite Granite () is a coarse-grained (phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies undergro ...

. It prefers locations with full sun exposure. It is common on exposed granite boulders and outcrops throughout its range, although it may readily be missed due to its small size. The lichen has a

, and is known from all continents. It is found in the maritime and continental Antarctic, including the

Antarctic Peninsula The Antarctic Peninsula, known as O'Higgins Land in Chile and Tierra de San Martín in Argentina, and originally as Graham Land in the United Kingdom and the Palmer Peninsula in the United States, is the northernmost part of mainland Antarctic ...

Queen Mary Land Queen Mary Land or the Queen Mary Coast () is the portion of the coast of Antarctica lying between Cape Filchner, in 91° 54' E, and Cape Hordern, at 100° 30' E. It is claimed by Australia as part of the Australian Antarctic Territory. It w ...

, and

Victoria Land Victoria Land is a region in eastern Antarctica which fronts the western side of the Ross Sea and the Ross Ice Shelf, extending southward from about 70°30'S to 78°00'S, and westward from the Ross Sea to the edge of the Antarctic Plateau. It ...

. In a study of the community structure of saxicolous lichens found on rock faces within a radius of the Mount Tokachi volcano in Japan, researchers found that ''Lecanora polytropa'' thrived in the volcanic environment (close to the active fumarole) that was intolerable for many other species. Its tiny thalli can insert into the small depressions and cracks on the rock, helping it gain a foothold and begin surface colonization even when faced with the

weathering Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs ''in situ'' (on site, with little or no movement), ...

associated with high winds and storms. ''Lecanora polytropa'' is also involved in the

succession Succession is the act or process of following in order or sequence. Governance and politics *Order of succession, in politics, the ascension to power by one ruler, official, or monarch after the death, resignation, or removal from office of ...

of lichens that appear on gravestones, and tends to maintain its presence long after its initial colonization.

Species interactions

''Lecanora polytropa'' is a known host to the lichenicolous fungus species '' Carbonea aggregantula'', ''

Carbonea supersparsa ''Carbonea supersparsa'' is a species of lichenicolous fungus belonging to the family Lecanoraceae. It is widespread in the Northern Hemisphere. In Iceland it has been reported growing on ''Lecanora cenisia'' near Egilsstaðir and ''Lecanora poly ...

'', ''

Carbonea vitellinaria ''Carbonea vitellaria'' is a species of lichenicolous fungus belonging to the family Lecanoraceae. It has a worldwide distribution. In Iceland it has been reported growing on '' Candelariella vitellina'' near Egilsstaðir Egilsstaðir () is a ...

'', '' Cercidospora epipolytropa'', '' Endococcus propinquus'', ''

Lichenoconium lecanorae ''Lichenoconium'' is a genus of fungi belonging to the family Lichenoconiaceae. The genus was circumscribed by Franz Petrak and Hans Sydow in 1927. Species The genus has a cosmopolitan distribution. , Species Fungorum accepts 16 species in ' ...

'', '' Muellerella erratica'', '' Muellerella lichenicola'', ''

Muellerella pygmaea ''Muellerella pygmaea'' is a species of lichenicolous fungus in the family Verrucariaceae. It has a cosmopolitan distribution in Arctic-alpine areas and grows on the thallus and apothecia of a number of hosts. Host species for ''Muellerella p ...

'' var. ''athallina'' and ''

Stigmidium squamariae ''Stigmidium'' is a genus of lichenicolous (lichen-eating) fungi in the family Mycosphaerellaceae. The genus was circumscribed by Italian botanist Vittore Benedetto Antonio Trevisan de Saint-Léon in 1860, with '' Stigmidium schaereri'' assigne ...

''.

Similar species

''Lecanora polytropa'' may be confused with '' L. fuscobrunnea'', which has larger apothecia (up to 1.6 mm wide) that are partially blackened to completely black, and may have a rudimentary stipe. In ''L. polytropa'', the apothecia are always

sessile Sessility, or sessile, may refer to: * Sessility (motility), organisms which are not able to move about * Sessility (botany), flowers or leaves that grow directly from the stem or peduncle of a plant * Sessility (medicine), tumors and polyps that ...

and not blackened.

References