Baeomyces carneus

Baeomyces carneus spreads as a crust that can cover patches of soil, rotting wood or sheltered rock up to about 10 cm across. The surface ranges from coarse powder-like granules to closely packed, scale-like squamules; around the edge these scales may radiate outward to give a faint, rosette (placodioid) outline. Colour is typically very pale green or light brown. Powdery soralia are scattered and sometimes absent, but minute, detachable flakes called schizidia—up to 0.3 mm wide and perfectly round—are usually abundant and serve as the main vegetative propagules. The algal partner consists of globose or slightly ellipsoid cells (6–14 μm in diameter) arranged in a continuous layer beneath the surface.^[4]

Sexual fruit bodies are rare in British material yet common elsewhere. When present they form pinkish-brown discs up to 2 mm wide that may sit directly on the crust or rise on a solid stalk (stipe) 0.5–4 mm tall, itself occasionally branched and dusted with tiny squamules. Internally, the spore-bearing layer (hymenium) is 65–110 μm thick and threaded by slender filaments (paraphyses) whose tips swell only slightly to about 2.5 μm. Each cylindrical ascus (60–90 × 8–10 μm) releases eight colourless, spindle-shaped ascospores measuring roughly 8.5–12 × 2.5–4.5 μm.^[4]

Chemical spot tests aid field identification: the thallus is negative with bleach (C−) but turns yellow then red with potassium hydroxide (K+ yellow → red), gives a red flash with the combined KC test, and reacts orange with paraphenylenediamine (Pd+). It shows no fluorescence under long-wave ultraviolet light (UV−). These reactions reflect abundant norstictic and connorstictic acids within the crust, while gyrophoric and lecanoric acids appear later and are restricted to mature apothecia.^[4]

It is widely distributed in the boreal forest region of North America,^[5] and also occurs in Europe, New Zealand, the West Indies, and Hawaii.^[3]