Oceanoplaca isidiosa
Oceanoplaca isidiosa is a species of lichen-forming fungus in the family Teloschistaceae. It forms bright yellow-orange to reddish-orange rosettes on rocks, particularly in coastal areas, and is known from Brazil and the Galápagos Islands. Originally described from granite along the Brazilian seashore in 1890, the species was transferred to the newly established genus Oceanoplaca in 2020 based on DNA studies, where it serves as the type species. The lichen reproduces primarily through small breakaway outgrowths and produces the rare pigment isidiosin, which was named after this species.
Taxonomy
Oceanoplaca isidiosa was originally described from granite rock on the seashore near Rio de Janeiro, Brazil, in 1890 by Edvard Vainio as Placodium isidiosum, based on an orange, tightly attached thallus with radiating marginal lobes and short isidia. Alexander Zahlbruckner transferred the species to Caloplaca in 1931.In a phylogenetic revision of Galápagos Teloschistaceae, Frank Bungartz, Ulrik Søchting, and Ulf Arup transferred the species to the newly described genus Oceanoplaca. In that treatment, Oceanoplaca is placed in the subfamily Caloplacoideae and is recovered as sister to Phaeoplaca, which was later renamed to Obscuroplaca.
Within the Galápagos, the species is morphologically variable, and some pale, whitish- forms were once suspected to represent a separate taxon; DNA data did not support splitting them. Weber had annotated some pruinose collections as "Caloplaca saxicola", but that name was never formally published and is treated as part of O. isidiosa.
Description
The thallus of O. isidiosa is . It consists of convex, elongated to radiating in the center and broader, fan-shaped lobes around the margin. Individual rosettes reach about 2.5 cm across, and neighboring thalli often merge. The surface is usually strong yellow-orange to deep reddish orange, sometimes with a faint orange dusting and only rarely a pale whitish pruina.Vegetative reproduction is typically prominent: the thallus is densely covered with isidia—tiny outgrowths that can break off and start new thalli. These begin as small or nodules and soon become broadly cylindrical to coarsely, about 0.1–0.2 mm thick. Apothecia are often absent or poorly developed when the thallus is heavily isidiate. When present, they are typically 0.6–0.8 mm wide, in form, and orange, with the initially concave and later flatter. Spores are produced eight per ascus and are, typically 9.2–11.6 × 5.4–7.6 μm, occasionally ranging to 8.3–13.1 × 4.6–9.2 μm. Pycnidia have not been observed.
Chemically, both thallus and apothecia react K+ purple, consistent with anthraquinone pigments. The species produces abundant quantities of the anthraquinone isidiosin; the compound was named after O. isidiosa, and its chemical structure has not yet been fully resolved.
Habitat and distribution
Oceanoplaca isidiosa was described from Brazil and is also known from the Galápagos Islands of Ecuador, where it was first reported in the literature in 1986. In the Galápagos it is primarily saxicolous, forming bright rosettes on rock in open sites.It most often occurs on sunny, wind- and rain-exposed rock surfaces, and is less frequent in sheltered, semi-shaded habitats. On the islands it is recorded mainly from the coastal zone through the dry and lower transition zones, and only rarely extends into the humid zone.