''Polycauliona coralloides'', the coral firedot lichen, is a species of small

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 ...

(bushy), saxicolous (rock-dwelling)

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 ...

in the family Teloschistaceae. First formally described in 1866, it was later shuffled to a few different

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 ...

in its taxonomic history before ending up in '' Polycauliona'', a genus resurrected from taxonomic obscurity in the

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 ...

era. The lichen occurs on seaside rocks in the intertidal spray zone of

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

and northwestern Mexico. The species is readily recognized due to its distinctive

coral Corals are colonial marine invertebrates within the subphylum Anthozoa of the phylum Cnidaria. They typically form compact Colony (biology), colonies of many identical individual polyp (zoology), polyps. Coral species include the important Coral ...

-like form–its

thallus Thallus (: 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. A thallus usually names the entir ...

grows as a tangle of orange, filamentous branches.

Taxonomy

''Polycauliona coralloides'', originally described as ''Placodium coralloides'' by Edward Tuckerman in 1864, has experienced several taxonomic revisions. It has been reclassified under various genera, including '' Polycauliona'', '' Thamnoma'', and '' Caloplaca''. This species, along with '' Caloplaca thamnodes'', is part of a group of dwarf-fruticose species that formerly belonged to the section ''Gasparrinia'' of genus ''Caloplaca''. It had been suspected, even before the advent of

, that this group was not

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 ...

, implying that these species have evolved separately from different ancestors within the genus. The presence of a microfruticose species in a predominantly crustose genus is unusual, and has led to historical disagreement as to its proper classification. In 2001, Irwin Brodo suggested that the fruticose growth form of the lichen hinted at a possible relationship to '' Teloschistes'', but further pointed out that the North American representatives of this genus were either corticolous or terricolous, and more abundantly branched. The

etymology Etymology ( ) is the study of the origin and evolution of words—including their constituent units of sound and meaning—across time. In the 21st century a subfield within linguistics, etymology has become a more rigorously scientific study. ...

of the species epithet ''coralloides'' alludes to the

-like appearance of the species. Phylogenetically, ''Polycauliona coralloides'' and '' Caloplaca thamnodes'' share similarities in thallus anatomy, spore type, overall

morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines *Morphology (archaeology), study of the shapes or forms of artifacts *Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies, ...

, and ecology, suggesting a close relationship. However, '' Caloplaca brattiae'' may also share a

common ancestor Common descent is a concept in evolutionary biology applicable when one species is the ancestor of two or more species later in time. According to modern evolutionary biology, all living beings could be descendants of a unique ancestor commonl ...

with ''P. coralloides'', as indicated by several similar features. It is commonly known as the "coral firedot lichen".

Description

''Polycauliona coralloides'' is a dwarf-

lichen that forms dense to loose cushions up to in diameter and in height. Its branches are , (or at least somewhat so) and can be erect, arched, or almost prostrate; they measure about 0.4 mm in diameter and are round and bumpy. The

is yellow to orange-yellow and may have pseudocyphellae in small depressions. Initially, ''P. coralloides'' forms elongated thallus that adhere closely to the , but over time, it evolves into a distinctly subfruticose thallus.

Apothecia An ascocarp, or ascoma (: ascomata), 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. As ...

are fairly common, , and can be at the ends of branches or long them. Their color is slightly darker than that of the thallus. The spores are and

ellipsoid An ellipsoid is a surface that can be obtained from a sphere by deforming it by means of directional Scaling (geometry), scalings, or more generally, of an affine transformation. An ellipsoid is a quadric surface; that is, a Surface (mathemat ...

, with a very thin

septum In biology, a septum (Latin language, Latin for ''something that encloses''; septa) is a wall, dividing a Body cavity, cavity or structure into smaller ones. A cavity or structure divided in this way may be referred to as septate. Examples Hum ...

. Chemically, the species is characterized by the presence of parietin as the major pigment, along with small amounts of emodin, teloschistin, parietinic acid, and fallacinal. The thallus and apothecia react K+ (purple), while the medulla shows negative reactions to standard chemical spot tests.

Similar species

''Polycauliona coralloides'' is often confused with ''Xanthoria'' cf. ''candelaria'' and '' Caloplaca thamnodes''. ''X. cf. candelaria'' differs by having flat lobes with an upper and lower surface and is mostly sorediate, which ''C. coralloides'' never is. ''C. thamnodes'', while closely related, can be distinguished by its little branched thallus, slightly thicker branches, darker orange color, and a more southern distribution. The New Zealand endemic '' Austroplaca erecta'' has some similarities to ''P. coralloides''. '' Austroplaca erecta'' is distinguished by its less prominent pseudocyphellae, differing lobe anatomy, wider ascospores with longer septa, and larger conidia. '' Caloplaca thamnodes'', found in Baja California, is a species similar to ''Polycauliona coralloides'' but is distinguishable by its less branched thallus, marginally thicker branches, and a more pronounced dark orange hue.

Habitat, distribution, and ecology

''Polycauliona coralloides'' is a strictly

littoral The littoral zone, also called litoral or nearshore, is the part of a sea, lake, or river that is close to the shore. In coastal ecology, the littoral zone includes the intertidal zone extending from the high water mark (which is rarely i ...

species, found close to the seashore, predominantly on hard rocks and mainly on vertical surfaces. It typically grows in the lower part of the supralittoral zone within a narrow vertical range. The species often occupies locations closer to the shore than '' Caloplaca rosei'' and '' Caloplaca brattiae'' and avoids sites exposed to bird manuring. As might be expected for a littoral species, it is quite tolerant to sea salt. The distribution of ''P. coralloides'' extends from northern

Baja California Baja California, officially the Free and Sovereign State of Baja California, is a state in Mexico. It is the northwesternmost of the 32 federal entities of Mexico. Before becoming a state in 1952, the area was known as the North Territory of B ...

, Mexico, to northern

Oregon Oregon ( , ) is a U.S. state, state in the Pacific Northwest region of the United States. It is a part of the Western U.S., with the Columbia River delineating much of Oregon's northern boundary with Washington (state), Washington, while t ...

. Its presence further south is possible, but not likely further north due to unsuitable habitats in these regions. It has also been documented in Channel Islands National Park. '' Stigmidium hesperium'' is a lichenicolous fungus, first described in 2009, that parasitises ''Polycauliona coralloides''. Infection by the fungus results in erosion and bleaching of the thallus and apothecia.

References

{{Taxonbar, from=Q26478680 Teloschistales Lichen species Lichens described in 1866 Lichens of Mexico Lichens of the Northwestern United States Lichens of the Southwestern United States Taxa named by Edward Tuckerman