Arthonia cyanea
Description : Thallus foliicolous, rounded, ±dispersed or continuous centrally, to 10 mm diam., smooth, grey, greenish grey to pale-green, matt. Prothallus indistinct. Apothecia round to angular 0.2–0.8 mm diam., plane, not prominent, usually at margins of algiferous thalline patches, bluish black but covered by a thin to thick white pruina imparting a ±bluish colour to apothecia. Epithecium dark-brown, upper parts with colourless granular crystals, 10–15 (–20) μm thick. Hymenium colourless 20–30 m tall. Hypothecium indistinct. Paraphysoids richly branched and anastomosing, c. 1 μm diam. Asci ovoid, 18–20 × 20–25 μm, 6–8-spored. Ascospores usually 3-septate (sometimes 2- or 4-septate), ±pyriform, distinctly macrocephalic (one of the terminal cells much larger than the other cells), not or only slightly constricted at septa, 15–20 × 4.5–6.5 (–7) μm.
N: Auckland (Waitakere Ra.). Abundant on leaves of shrubs and bark of Metrosideros excelsa (Bartlett 1988). Known also from Kenya, Papua New Guinea, New Caledonia, Tasmania, Mexico, southern South America (Aptroot et al. 1995; Lücking & Kalb 2001; McCarthy et al. 2001; Lücking et al. 2003; Herrera-Campos et al. 2004).
Pantropical
Illustrations : Santesson (1952: 78, fig. 7); Lücking (1992: 23, fig. 2C– E); Thor et al. (2000: 38, fig. 3 I, K); Malcolm & Malcolm (2001: 39, 41).
Arthonia cyanea is easily recognised by: the foliicolous habit; and its bluish, pruinose ascocarps, which are not readily confused with any other foliicolous species of Arthonia.
