''Physcia stellaris'' is a species 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.isidia An isidium is a vegetative reproductive structure present in some lichens. Isidia are outgrowths of the thallus surface, and are corticated (i.e., containing the outermost layer of the thallus), usually with a columnar structure, and consisting o ...

lobule In anatomy, a lobe is a clear anatomical division or extension of an organ (as seen for example in the brain, lung, liver, or kidney) that can be determined without the use of a microscope at the gross anatomy level. This is in contrast to the m ...

s, soredia and pruina.It tests positive K+ yellow upper cortex with a 10%

potassium hydroxide Potassium hydroxide is an inorganic compound with the formula K OH, and is commonly called caustic potash. Along with sodium hydroxide (NaOH), KOH is a prototypical strong base. It has many industrial and niche applications, most of which exp ...

solution. In North America, it is known colloquially as the fringed rosette lichen. It can grow as an

epiphyte An epiphyte is an organism that grows on the surface of a plant and derives its moisture and nutrients from the air, rain, water (in marine environments) or from debris accumulating around it. The plants on which epiphytes grow are called phoroph ...

. In

Greece Greece,, or , romanized: ', officially the Hellenic Republic, is a country in Southeast Europe. It is situated on the southern tip of the Balkans, and is located at the crossroads of Europe, Asia, and Africa. Greece shares land borders with ...

, it has been reported from the trunk of ''

Platanus ''Platanus'' is a genus consisting of a small number of tree species native to the Northern Hemisphere. They are the sole living members of the family Platanaceae. All mature members of ''Platanus'' are tall, reaching in height. All except f ...

'' trees.

Taxonomy

It was initially described as ''Lichen stellaris'' by Carolus Linnaeus in 1753 before receiving its own genus of ''Physcia'' in 1856 by William Nylander.

Description

The

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 ...

of ''Physcia stellaris'' can be described as foliose as it has aspects of leaf-like lichen structures. The size and shape of the thallus is irregular and can grow up to 4 cm in diameter. Lobes are loosely

appressed This glossary of botanical terms is a list of definitions of terms and concepts relevant to botany and plants in general. Terms of plant morphology are included here as well as at the more specific Glossary of plant morphology and Glossary o ...

and are on average only 0.5 mm in size. The upper surface is whitish grey, appearing as almost a cream color. It lacks any form of soredia or isidia on the upper surface. The lower surface is white to brown with simple

rhizines In lichens, rhizines are multicellular root-like structures, arising mostly 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 ...

. Apothecia are abundant varying in size from 0.5mm-1.5mm and have fruiting bodies shaped like a plate with a ring around them called

lecanorine A lichen has lecanorine fruiting body parts if they are shaped like a plate with a ring around them, and that ring is made of tissue similar to the main non-fruiting body part of the lichen.Field Guide to California Lichens, Stephen Sharnoff, Yale ...

Ascocarp An ascocarp, or ascoma (), is the fruiting body ( sporocarp) of an ascomycete phylum fungus. It consists of very tightly interwoven hyphae and millions of embedded asci, each of which typically contains four to eight ascospores. Ascocarps are m ...

containing 8 brown, septate ascospores ranging in size from 15-18

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 ...

. Is found as a lichen in all forms. ''Physcia stellaris'' can be differentiated from all other ''Physcia'' species due to lack of soredia, with exception to '' P. aipolia. P. aipolia'' can be differentiated from ''P. stellaris'' due to ''aipolia’s'' broader lobes and apothecia that tend to be pruinose.

Distribution and habitat

This species is commonly found lichenized on bark and rock all across the

temperate zones In geography, the temperate climates of Earth occur in the middle latitudes (23.5° to 66.5° N/S of Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ranges throughout t ...

of North America as well as parts of Europe. Documented findings of this species range from Georgia to the Canadian Northwest Territories. The species is quite common on deciduous trees but can also be found less commonly on

conifers Conifers are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up the division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single extant class, Pinopsida. All extan ...

Reproduction

''Physcia stellaris'' shows no evident means of asexual reproduction due to its lack of isidia or soredia. This species has abundance of apothecia that allow for sexual reproduction.

References

{{Taxonbar, from=Q292035 stellaris Taxa named by Carl Linnaeus Lichens described in 1753 Lichens of North America Lichen species