Lecanora albellula is a
crustose lichen, meaning it grows tightly against its surface like a crust. Its main body (
thallus) consists of small, scattered warty bumps or forms a continuous warty-cracked surface. These rounded wart-like measure 0.05–0.15 mm across, range from moderately to strongly convex, and vary in colour from yellowish-green to
ochre or greyish-beige. Sometimes, a greyish-white foundation layer () can be seen around individual thalli. The thallus can reach up to 4 cm in width and ranges from 50 to 600 μm in thickness. The surface is or slightly shiny. The photobiont (algal) cells within the thallus are and measure 8–20 μm in diameter. The thallus of
L. albellula is often inconspicuous, consisting of scattered granules or being immersed in bark, making it difficult to distinguish in the field. The reproductive structures (
apothecia) are round to irregular in shape and usually appear in dense clusters, though they occasionally grow alone or in small groups. They attach to the surface with a constricted base and measure 0.35–0.40 mm across on average, reaching up to 0.6–0.9 mm. The of each apothecium is light ochre to reddish-brown in colour, with a matt appearance and a fine whitish . The disc is flat to moderately convex, rarely strongly convex. Each apothecium has a rim (margin) that is initially slightly raised but becomes level with the disc or disappears in older specimens. This margin is yellowish-beige to ochre (matching the colour of the thallus warts when present) and has a matt appearance, often with an irregular or knobby texture. The (outer layer of the apothecium) has a cortex that is best developed in its lower part, measuring 10–30 μm thick. Examined microscopically, the spores () are colourless and (without internal divisions), measuring 8.7–10.8
μm long and 4.1–4.8 μm wide. The hymenium (spore-producing layer) is
hyaline with occasional orange-brown granules and measures 35–55 μm in height. The
paraphyses (sterile filaments between the spore-producing cells) are simple to sometimes branched or anastomosing, measuring 1.5–2 μm wide, with tips occasionally widening to 4–5 μm. Unlike some closely related species,
Lecanora albellula produces four distinct types of
conidia, which are microscopic asexual spores involved in reproduction. These include crescent-shaped macroconidia (often present), 7–10 (sometimes up to 14) × 1–2 μm, 1–3-septate, curved; microconidia (frequent), 5.5–10 × 0.8–1.3 μm, slender and slightly curved; mesoconidia (rare), 3–5 × 1.5–2 μm, ellipsoidal; and leptoconidia (rare), 20–25 × 0.7–1 μm, curved.
Lecanora albellula demonstrates some variability in its anatomical structure, particularly in the organisation of the tissue layers in its apothecia. In older specimens, the margin may become less distinct, giving the apothecia a () appearance, though they retain their underlying structure when examined microscopically. These morphological features help distinguish European specimens of
L. albellula from the superficially similar North American taxon now known as "Lecanora sp. D", which tends to have slightly larger apothecial discs, a higher hymenium, and somewhat different amphithecial cortex development.
Similar species Within the
Lecanora saligna group,
Lecanora sarcopidoides is often mistaken with
L. albellula due to their similar morphology and overlapping distribution. However,
L. sarcopidoides can be distinguished by its more prominently pruinose apothecia, which often appear eroded or irregularly notched at the edges, whereas
L. albellula typically has weakly pruinose to non-pruinose apothecia with a smoother, more uniform margin. Chemically,
L. sarcopidoides contains
pseudoplacodiolic acid, while
L. albellula primarily produces isousnic acid. This distinction is critical, as historical herbarium specimens labeled as
L. albellula were frequently found to belong to
L. sarcopidoides upon re-examination using thin-layer chromatography. The two species also differ in conidial morphology:
L. albellula produces four distinct types of conidia, including crescent-shaped macroconidia, whereas
L. sarcopidoides lacks macroconidia entirely. Recent surveys suggest that
L. sarcopidoides may be more common in certain habitats, particularly on deadwood of
Picea abies in Bavarian forests, raising the possibility that some records of
L. albellula in Europe were misidentifications. Several European species in the
Lecanora varia group resemble
L. albellula but can be distinguished by their morphological, chemical, and ecological characteristics.
Lecanora burgaziae, described from central Spain, is similar in appearance but has a greenish, often endosubstratal thallus, apothecial discs lacking pruina, and contains
psoromic acid in addition to usnic acid.
Lecanora densa, another lookalike, differs with its beige to orange-brown, pruinose apothecial discs and a warted-areolate thallus, while
Lecanora varia has a prominent, two-layered apothecial margin and contains only psoromic acid. Additionally,
Lecanora coniferarum can be confused with
L. albellula, but it has a basally thickened amphithecial cortex, reddish-brown apothecial discs, and a narrower spore width.
Lecanora coppinsii, a related species found in Scotland, differs from
L. albellula by its smaller ascospores (6–8.5 by 2.5–3.5 μm), shorter microconidia (4.5–5.5 by ~1 μm), lack of macroconidia, and a less well-developed thalline margin.
Chemistry Chemical
spot tests for
L. albellula show no reaction with C, KC, or Pd reagents, while K produces a weak yellow reaction. The thallus contains
isousnic acid as the primary metabolite, with
usnic acid occasionally present in minor amounts. Traces of 7-
O-methylnorascomatic acid occur rarely, and only in the apothecia. In
acetone extracts, isousnic acid appears as weakly gelatinous with broadened, clustered granules to spiny globules, which appear weakly yellowish under normal light and do not
fluoresce under
UV light. When treated with
iron(III) chloride, the extract produces a red-brown reaction. ==Habitat and distribution==