Allographa cerradensis
Allographa cerradensis is a species of lichen-forming fungus in the family Graphidaceae. Found in Brazil, it was described as new to science in 2011 as Graphis cerradensis but in 2018 it was transferred to its current genus, Allographa. This bark-dwelling lichen forms thin, pale greenish-grey crusts with distinctive elongated fruiting bodies that snake across the surface in wavy lines. It is known only from its original discovery location in a Brazilian savanna reserve, where it grows in humid patches of dense Cerrado vegetation.
Taxonomy
Graphis cerradensis was described as new to science in 2011 by Marcelo Marcelli, Michel Benatti, and Robert Lücking on the basis of material collected in November 2007 from the Mogi-Guaçu Biological Reserve in São Paulo State, Brazil. The specific epithet refers to the Cerrado biome—the seasonally dry yet humid savanna–woodland mosaic—where the holotype was found.The species was subsequently transferred by Lücking and Klaus Kalb to the genus Allographa in 2018 as part of a major reorganization of the script lichen genera Graphis and Hemithecium. This transfer resulted in the current accepted name Allographa cerradensis.
The authors originally assigned Graphis cerradensis to the Graphis cinerea species group, a set of robust bark-dwelling lichens characterised by prominent, often grooved , a heavily blackened excipulum, and a hymenium suffused with tiny oil droplets. Within that group A. cerradensis is unique in combining a stictic acid chemistry with large, brick-walled ascospores; its closest look-alike, A. insperso-stictica, has narrower lirellae and spores divided only by cross-walls.
Description
The lichen forms a thin, continuous thallus up to 5 cm across and 30–70 micrometres thick. Its surface is smooth to slightly uneven,, and pale greenish-grey, lacking any dark boundary line. In vertical section the upper is, the internal irregular, and large clusters of crystals are scattered throughout—features that impart a faint speckled appearance.Reproductive structures are elongate lirellae, 1–3 mm long and 0.5–0.6 mm wide, that snake flexuously across the thallus. Each lirella is rimmed by a thick, white extension of the thallus that completely covers the dark inner lips. Beneath this margin lies a fully carbonised excipulum, 70–150 μm wide, whose jagged crest is just visible in transmitted light. The hymenium is 150–200 μm tall and densely infilled with minute that dissolve quickly in potassium hydroxide solution, clearing the view of the slender paraphyses and spore-bearing asci. Asci are spindle- to club-shaped, 130–180 × 30–40 μm, and usually contain four to eight ascospores. The colourless ascospores are oblong, 80–100 × 15–20 μm, and divided by 15–25 cross-walls and one to three longitudinal walls per segment, giving a brick-like pattern; they are roughly six to seven times longer than wide. Thin-layer chromatography detects stictic acid as the sole secondary metabolite.
The South African species Allographa oldayana is similar in appearance to A. cerradensis, but can be distinguished by its clearer hymenium, larger ascospores, and the presence of the compound hirtifructic acid.