Gyalectaria diluta

Gyalectaria diluta grows as a thin, crust-forming lichen that bleaches the underlying bark to pale green-grey or whitish tones. The crust breaks into tiny, smooth polygons (areoles only 0.2–0.3 mm across) that soon fuse into patches as large as about 6 × 2 cm. Viewed in section, the thallus is stratified: a firm outer cortex 10–40 μm thick overlies a layer of densely packed green algal cells (photobiont) 20–100 μm deep; no darker hypothallus is present. The algal partner consists of jelly-sheathed, angular cells roughly 10–14 μm wide. Standard spot tests are negative (C−), indicating the absence of gyrophoric acid; thin-layer chromatography shows an as yet unidentified substance instead. Reproduction takes place in countless wart-like swellings (verrucae) that cover older parts of the crust at densities up to 119 per square centimetre. Each verruca usually houses a single tiny apothecium 0.20–0.36 mm in diameter whose disc is sunk below the surface, later rupturing the wart and exposing a flat to shallowly concave salmon-to-pale-yellow centre framed by the thallus itself. Around the disc lies a distinct, waxy pseudo-excipular rim up to 65 μm thick whose inner tissue stains bright blue in iodine after potassium pre-treatment, revealing starch-like compounds. …

The lichen is restricted to very humid, late-successional conifer forests. It has been recorded on the bark of western hemlock (Tsuga heterophylla), western redcedar (Thuja plicata), Douglas-fir (Pseudotsuga menziesii), and occasionally on decorticated logs where it may mingle with Absconditella lignicola and Lichinodium sirosiphoideum. Although capable of colonising a range of substrates, it occurs most reliably on the smooth bark of young redcedar saplings growing beneath an old-growth canopy. Known sites form a loose arc through the inland temperate rain-forest belt: fourteen localities in British Columbia, one in northern Idaho and one in north-western Montana. Elevations range from sea level along the rugged mid-coast to about 1,000 m (3,300 ft) in the Selkirk and Cabinet Mountains. All stands share a persistently moist microclimate and have escaped large-scale disturbance for centuries, suggesting the species is sensitive to canopy removal and prolonged drying.

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