Micarea sipmanii

The lichen forms a very thin, cortex-lacking (ecorticate) crust of whitish- to bluish-grey granules, each usually less than 0.1 mm across, scattered or loosely clustered on smooth bark. The thallus contains gyrophoric acid, giving a C+ (red) reaction, while spot tests are otherwise negative.^[2]

Apothecia may be absent or abundant. When present they are 0.1–0.5 mm wide, convex to hemispherical, often tuberculate and proliferating over older discs; the margin is lacking and the disc ranges from pale orange-brown to bluish-grey. The exciple is reduced, composed of branched hyphae; the hymenium is 50–65 μm high and stains reddish in nitric acid. Asci (usually eight-spored) are 40–55 × 12–15 μm and amyloid; the oblong-fusiform ascospores are 7-septate, 27–33 × 4–4.5 μm.^[2]

Asexual structures are striking: numerous arbuscular (shrub- or treelike) pycnidia stand on delicate, often branched stalks 1.4–2.2 mm long, each bearing an inflated, rostrate head up to 0.3 mm wide that is thinly hairy and translucent. The pycnidium cavity is packed with filiform conidia, 44–52 × 1–1.2 μm, mostly aseptate (lacking internal partitions, or septa) but occasionally 1–3-septate.^[2]

The species is known only from the type locality on Basse-Terre, Guadeloupe, where it grows on the vertical trunk of a smooth-barked tree in extremely wet, mid-elevation rainforest near the famous Chutes du Carbet waterfalls. Despite later surveys in similar habitats on the island, no additional populations have been found.^[2]