Flora of New Zealand Series

Description : Thallus crustose, in small, irregular patches or bands on smooth bark, 5–10 mm diam., thin to thick, continuous in parts to areolate, verrucose, or occasionally here and there sorediate, pale yellowish white or pale greenish to pale grey-white, margins effuse, without a delimiting prothallus. Apothecia crowded, 0.1–0.5(–1) mm diam., disc plane at first soon becoming noticeably convex to conglomerate, yellowish, waxy to matt, epruinose. Thalline margin concolorous with thallus, verrucose, most noticeable in young fruits, becoming ±excluded with age. Amphithecium with large crystals not dissolving in K (pulicaris -type). Parathecium 15 μm thick, colourless, with many small crystals, not dissolving in K. Epithecium yellow-brown to 15 μm thick. Hymenium hyaline, 55–65 μm tall. Hypothecium colourless. Ascospores ellipsoidal, 8.5–14 × 5–7 μm.

Chemistry : Thallus and apothecial margins: K+ yellow, C−, KC−, Pd+ yellow-orange; containing as major compounds atranorin and 2'- O- methylperlatolic acid; as minor compounds chloroatranorin, 2'- O- methylhyperlatolic, 2'- O- methylisohyperlatolic and 2'- O- methylsuperlatolic acids, ±arthothelin.

N: Northland (Whangarei), Auckland (The Domain, Western Springs Park). On mangroves (Avicennia marina) and exfoliating bark of Platanus in parks and gardens. Still rather poorly collected (Galloway et al. 2001a: 32). Known also from Baja California, the West Indies, Central and South America, South Africa, Zimbabwe, Madagascar, Oceania and Australia (Lumbsch 1994; Guderley 1999: 207; Becker 2002; McCarthy 2003c, 2006; Lumbsch & Elix 2004; Ryan et al. 2004b: 226–227).

Pantropical

Illustrations : Lumbsch (1994: 99, fig. 60C–F); Guderley (1999: 204, fig. 18C, D); Ryan et al. (2004b: 227, fig. 33).

Exsiccati : Lumbsch & Feige, Lecanoroid Lichens. Fasc. 2 No. 30 (1993).

Lecanora helva is characterised by: the corticolous habit; the small, irregular, pale yellow-white to grey-green, minutely warted thalli; the crowded apothecia with convex–conglomerate, waxy yellow discs, and a verrucose thalline margin concolorous with the thallus. Morphologically it is similar to L. leprosa. Both are pantropical species. Chemically they are easily distinguished: L. leprosa contains the gangaleoidin and atranorin chemosyndromes (Lumbsch & Elix 1993: 72) while atranorin and 2'- O- methylperlatolic acid are major compounds in L. helva, with chloroatranorin, 2'- O- methylhyperlatolic, 2'- O- methylisohyperlatolic and 2'- O- methylsuperlatolic acids as minor compounds. The species is discussed in detail in Lumbsch (1994: 100–103).