Lithothelium

Taxonomy

The genus was circumscribed by the Swiss botanist Johannes Müller Argoviensis in 1885, with L. cubanum as the type species. Müller distinguished Lithothelium from related genera by its crustose, often inconspicuous thallus and distinctive fruiting bodies (apothecia) that are immersed in the substrate in clustered arrangements, with convergent openings arranged in a collar-like formation. He noted that the genus was similar in composition to Sagedia, characterized by plurilocular spermogonia and hyaline, transversely divided spores arranged in bead-like chains within the asci. The type species L. cubanum was described from specimens collected on calcareous rock in Cuba, featuring a very thin thallus and distinctive black, clustered perithecia with multiple ostioles.

Description

Lithothelium is a genus of crustose lichens, meaning its thallus—the main body of the lichen—forms a thin, crust-like layer that can either remain embedded within the substrate or lie on its surface. Some species have a green algal partner from the genus Trentepohlia, while others may lack a altogether.

The reproductive structures, called perithecia, are flask-shaped fruiting bodies that are typically black and can occur either individually or in fused clusters. These have an ostiole—a small opening through which spores are released—that is usually located at the top but may also be offset to the side. Inside the perithecia, the fertile tissue (the ) consists of slender, unbranched or slightly branched filaments called paraphyses. These lack , which are short hairs found in some other lichenised fungi. The gel that surrounds the hymenium (spore-producing layer) may show weak blue or orange staining in iodine-based staining, although the ascus wall itself does not react (K/I–). The asci usually contain 6 to 8 spores and typically have a rounded or three-lobed () , a small structure near the apex that assists in spore discharge.

The ascospores may be colourless or brown, with three to seven cross-walls (septa) or occasionally with a more complex somewhat (brick-like) structure. All septa are —meaning the cross-walls are thickened and distinct—and the individual spore compartments (cell ) tend to be rounded in shape. Asexual reproduction occurs through pycnidia, small specialised structures that produce long, threadlike (), non-septate conidia. No secondary metabolites (lichen products) have been detected in this genus using thin-layer chromatography.

Ecology

Species of Lithothelium are found growing either on tree bark or on rock surfaces. They resemble those in the genus Pyrenula, but can generally be distinguished by the presence of an ocular chamber in the asci and the more rounded appearance of their spore cells.

Species

• Lithothelium austropacificum – Lord Howe Island
• Lithothelium bermudense – Bermuda
• Lithothelium cubanum
• Lithothelium echinatum – China
• Lithothelium filisporum
• Lithothelium fluorescens
• Lithothelium fugax
• Lithothelium grossum – China
• Lithothelium hieroglyphicum – Australia
• Lithothelium hyalosporum
• Lithothelium illotum
• Lithothelium immersum
• Lithothelium insulare – India
• Lithothelium kantvilasii – Australia
• Lithothelium kiritea – New Zealand
• Lithothelium obtectum
• Lithothelium phaeosporum
• Lithothelium quadrisporum – Thailand
• Lithothelium quiescens – Christmas Island

References

References

1. {{cite Q. Q126009229
2. Aptroot, André. (2006). "Three new species of ''Lithothelium'' (Pyrenulaceae) from China and Thailand, with a revised world key and annotated list of species". The Lichenologist.
3. Aptroot, André. (2007). "New species, combinations, lectotypifications and synonyms in Australia Pyrenulaceae". Australasian Lichenology.
4. (2008). "Pyrenocarpous lichens with bitunicate asci". Bibliotheca Lichenologica.
5. (2016). "''Lithothelium bermudense'' sp. nov., a new saxicolous lichen from Bermuda". Mycotaxon.
6. (2023). "Perithecial genera I, including ''Acrocordia'', ''Alloarthopyrenia'', ''Anisomeridium'', ''Antennulariella'', ''Arthopyrenia'', ''Celothelium'', ''Cyrtidula'', ''Dichoporis'', ''Eopyrenula'', ''Julella'', ''Leptorhaphis'', ''Leptosillia'', ''Lithothelium'', ''Mycomicrothelia'', ''Mycoporum'', ''Naetrocymbe'', ''Pyrenula'', ''Rhaphidicyrtis'', ''Sarcopyrenia'', ''Swinscowia'' and ''Tomasellia''".
7. (2001). "Contributions to the lichen flora of the Lakshadweep (Laccadive) Islands, India". The Lichenologist.
8. McCarthy, P.M.. (1996). "''Lithothelium austropacificum'' sp. nov. (Pyrenulaceae) from Lord Howe Island, Australia". The Lichenologist.
9. McCarthy, P.M.. (2001). "The genus ''Lithothelium'' (Pyrenulaceae) in Christmas Island, Indian Ocean". Australasian Lichenology.
10. McCarthy, Patrick. (2015). "A new species of ''Lithothelium'' (lichenized Ascomycota, Pyrenulaceae) from the Tarkine region, north-western Tasmania". Telopea.
11. (1885). "Pyrenocarpeae Cubenses a cl. C. Wright lectae". Botanische Jahrbücher für Systematik, Pflanzengeschichte und Pflanzengeographie.
12. "Synonymy'': ''Lithothelium Müll. Arg., Bot. Jb. 6: 386 (1885)". [[Species Fungorum]]].
13. (2020). "Outline of Fungi and fungus-like taxa". Mycosphere.