Inoderma nipponicum

The thallus (lichen body) forms pale olive-grey patches that are fissured to fissured-areolate and lack a true outer skin (ecorticate), giving a matt, faintly felty or scurfy surface; a loose, thin necrotic layer often overlies the algal layer. The photobiont is a trentepohlioid green alga (Printzina lagenifera); cells are mostly 9–19 × 5–14 micrometres (μm), and calcium oxalate crystals were not seen in the type material.^[2]

Sexual fruiting bodies (apothecia) were sparse and under-developed in the type material. When present they are small rounded discs, 0.4–0.6 mm in diameter, set level with the thallus and covered in a thin white pruina (a frost-like powder). Internally the tissues and spore-bearing layer match the Arthonia-type; ascospores are hyaline, narrowly obovate, typically 3–4-septate (rarely 2) and measure about 13–16 × 3–4 μm.^[2]

Asexual fruiting bodies (pycnidia) are numerous and conspicuous: dark brown to black cups 0.25–0.50 mm across that protrude strongly or sit with a constricted base on the thallus, their rims and shoulders dusted with thick white pruina. The pore is entire to ragged, and the interior shows a bowl-shaped cavity; the wall is strongly carbonised at the sides. Conidiogenous cells are 9–11 × 1.5–3.0 μm and produce bacilliform conidia that are often slightly curved, with dimensions averaging around 4.9 × 1.3 μm.^[2]

Chemically, the species contains lepraric acid. In routine spot tests the thallus and the white pruina turn K+ (lemon yellow), a diagnostic reaction for this compound, and are C−, KC−, Pd−; the thallus hyphae are I− but KI+ (pale blue).^[2]

Within Inoderma, I. nipponicum is most similar to I. subabietinum but differs consistently in lacking confluentic acid and in pycnidial traits: older pycnidia do not develop outwardly reflexed rims and carry a fine, mealy pruina rather than a coarse, granular one; its asexual spores (conidia) are often very slightly curved. Sterile material of I. byssaceum can appear similar, but that species has a K− thallus and pycnidia (no yellow reaction in the standard K test) and conidia that are a bit shorter and not weakly curved.^[2]

Inoderma nipponicum occurs below about 500 m elevation in shady to semi-shady situations. It grows mainly on deeply fissured or flaky bark of both deciduous and coniferous hosts, including Acer buergerianum, Machilus thunbergii, Picea sp., Pinus densiflora and Torreya nucifera; a small saxicolous collection was also made on rain-shadowed castle walls at Hikone. The species appears tolerant of drier conditions and of urban air, occurring in parkland as well as in old-growth forest. Confirmed records are from Japan (Hokkaidō and Honshū).^[2]