Rinodina exigua
≡Lichen exiguus Ach., Lichenogr. suec. prodr.: 69 (1799)["1798"].
Description : Thallus corticolous, lignicolous, white to pale-grey, continuous to cracked, warted, often with copious black granules, without a prothallus. Apothecia lecanorine, sessile or innate, numerous, crowded, deformed through mutual pressure, to 0.5 mm diam.; disc black, plane to convex. Thalline margin concolorous with thallus, thick, entire, prominent, becoming thinner and at length excluded, often strewn with black granules. Parathecium 10–15 μm wide, hyaline, brownish in upper parts. Cortex indistinct, to 10 μm thick, I−, photobiont layer bordered by a narrow, opaque zone filled with crystals of atranorin. Epithecium to 15 μm thick, grey-brown. Hymenium 80–90 μm tall. Paraphyses 1.5–3 μm thick, apices capitate, 3–5 μm diam. Hypothecium 50–60 μm thick. Asci Lecanora -type. Ascospores Physcia -type, often curved, ontogeny type A, torus well-developed, (15–)17–19 × 7–9 μm. Conidia bacillar, 4–5 × 1 μm.
Chemistry : Cortex K− or + sordid-yellowish, Pd+ yellow; containing atranorin.
N: Northland (Bay of Islands). Earlier records of R. exigua from Waiau and Arundel (Mayrhofer 1985: 511) refer to R. boleana and R. pyrina (Prof. Dr H. Mayrhofer, pers. comm.). Known also from Great Britain, Europe, Scandinavia, North America (Fox & Purvis 1992; Nimis 1993; Santesson 1993; Esslinger & Egan 1995; Scholz 2000; Nimis & Martellos 2003; Santesson et al. 2004).
Bipolar
Illustrations : Foucard (1990: pl. 293); Ropin & Mayrhofer (1993: 782, fig. 3); Wirth (1995b: 833); Nordic Lichen Flora 2 (2002: 103).
Rinodina exigua is characterised by: the corticolous habit; the pale thallus; the indistinct cortex; and the presence of atranorin. An early reference to Lecanora exigua (Hooker & Taylor 1844) refers to a species of Lecanora in the subfusca -group (specimen in BM). Specimens referred to by Hellbom (1896) collected by Sven Berggren from fruit trees were not seen. The occurrence of R. exigua in New Zealand must therefore remain doubtful.
