# Inoderma

Inoderma is a genus of lichen-forming fungi in the family Arthoniaceae. It was resurrected for use in 2015 for a small group of species with the following features: elevated, white pruinose pycnidia, immersed to adnate white pruinose apothecia, and a weakly gelatinized hymenium. Inoderma byssaceum was assigned as the type species for the genus.

## Description

Inoderma is a genus of lichens that typically forms broad, pale, whitish to light olive-grey patches on its substrate. These patches (the thallus) can be continuous but often develop a network of fine cracks or appear as tiny, powdery granules. The surface is usually not covered by a protective "skin" (cortex) and can feel slightly soft or powdery. The lichen's green partner cells (the photobiont) belong to Trentepohlia, a genus of green algae.
Some Inoderma species produce apothecia—small, often rounded, and slightly raised structures where spores are formed. These may lie flush with the lichen's surface or sit just above it, and they sometimes carry a thin to thick white powdery coating (pruina). The boundary between the apothecium and the main lichen body (the true exciple) is not clearly defined. Inside the apothecium, the spore-producing tissue (the hymenium) is colourless to pale yellowish-brown, with tiny pale crystals in its upper layer (the epithecium). Beneath this, the hypothecium is made of tangled fungal filaments within a jelly-like matrix, ranging in colour from pale to dark brown. Thin, thread-like structures called paraphysoids run through this layer, and their tips do not widen or darken. The asci, which are the spore-containing "sacs", follow the Arthonia-type structure and do not show a blue staining reaction with iodine solutions. The spores are typically elongated, sometimes slightly egg-shaped (cylindric-obovoid or soleiform), and divided into two to four compartments by internal walls (septa). They remain colourless and do not narrow at the dividing lines.
In addition to apothecia, Inoderma may also form conidiomata—tiny, elevated, spore-producing bumps called pycnidia. These pycnidia have dark brown to black walls and are often dusted with a thick layer of white powder. They release small, rod-shaped spores known as conidia.
From a chemical perspective, Inoderma species may contain substances such as lepraric acid and confluentic acid, along with some compounds not yet fully identified ("byssaceum unknowns"). When tested with chemicals, the dark brown pigments in the apothecia and pycnidia turn greenish-black in the K spot test and slowly shift to an orange-brown colour when treated with nitric acid. These reactions, along with the lichen's distinct physical features and internal structures, help distinguish Inoderma from related genera.

## Species

As of December 2024, Species Fungorum (in the Catalogue of Life) accepts six species of Inoderma:
* Inoderma afromontanum Frisch & G.Thor (2015) – Uganda
* Inoderma byssaceum (Weigel) Gray (1821)
* Inoderma epigaeum (Pers.) Gray (1821)
* Inoderma nipponicum Frisch, Y.Ohmura & G.Thor (2015) – Japan
* Inoderma sorediatum Ertz, Łubek & Kukwa (2018) – Poland
* Inoderma subabietinum (Coppins & P.James) Ertz & Frisch (2015) – Europe