Placidiopsis hypothallina is a species of saxicolous (rock-dwelling) crustose lichen in the family Verrucariaceae, described as a new species in 2002. It is unique within its genus for its thallus primarily composed of a hyphal resembling a found in some non-lichenised ascomycetes. It is found in Brazil and Taiwan.
Described by the Dutch lichenologist André Aptroot in 2002, Placidiopsis hypothallina was identified from collections made in the in Minas Gerais, Brazil.
The thallus of Placidiopsis hypothallina is crustose, typically covering rounded areas up to 0.5 cm in diameter. It features a distinctive consisting of loose, blackish hyphae with numerous isolated . These squamules are dark brown, flat, and rounded to , measuring 50âÂÂ200 üm in diameter and 50âÂÂ100 üm thick, each bordered by a thin black margin.
The upper of the squamules is dark brown and cellular, about 3âÂÂ5 üm thick, while the medulla is and hyaline (translucent). The are fully immersed within the thallus, (pear-shaped), and hyaline, measuring 50âÂÂ80 üm in diameter. The ostiole (opening) of each perithecium is centrally located, appearing as a black dot from above, and measures 30âÂÂ50 üm wide.
Asci (spore-bearing structures) are pyriform, approximately 25âÂÂ35 by 8âÂÂ13 üm, and do not possess an ocular chamber. Ascospores are hyaline, 1-septate, long-ellipsoid to , measuring 8âÂÂ10 by 2.5âÂÂ3 üm, and are arranged irregularly within the asci. No pycnidia have been observed to occur in this species.
Chemically, the species shows no reactions to standard lichen spot tests (KâÂÂ, CâÂÂ, UVâÂÂ), indicating the absence of detectable secondary metabolites.
Placidiopsis hypothallina is found growing on sun-exposed siliceous rocks, often accompanied by species of the foliose lichen genus Xanthoparmelia. At the time of its original publication in 2002, it had only been recorded from its type location in Brazil. Its known range was extended considerably the following year, when Aptroot recorded it from Taiwan. Those specimens were found growing parasitically on an undescribed species of Trapelia that itself was growing on volcanic rock. It has also been found in the Serra de Maracaju, Mato Grosso do Sul, Brazil.