Lecanora polytropa
Lecanora polytropa, commonly known as the granite-speck rim lichen, is a species of saxicolous lichen in the family Parmeliaceae. A small, inconspicuous species that grows in the cracks of rock surfaces, it has a cosmopolitan distribution and has been recorded on all continents, including Antarctica. Taxonomy. It was originally described by German botanist Jakob Friedrich Ehrhart in 1796 as a species of "Verrucaria". Gottlob Ludwig Rabenhorst transferred it to the genus "Lecanora" in 1845. It is commonly known as the granite-speck rim lichen. Description. "Lecanora polytropa" has a scanty thallus, 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. Ascospores are ellipsoid and measure 8–15 by 5–7 μm. Habitat and distribution. "Lecanora polytropa" grows on siliceous rock, particularly granite. 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 cosmopolitan distribution, and is known from all continents. It is found in the maritime and continental Antarctic, including the Antarctic Peninsula, Queen Mary Land, and Victoria Land. 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 associated with high winds and storms. "Lecanora polytropa" is also involved in the succession 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 supersparsa", "Cercidospora epipolytropa", "Endococcus propinquus" and "Muellerella pygmaea" var. "athallina" 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 and not blackened.