Pertusaria xanthoplaca
Description : Thallus dull- to bright-yellow, areolate, surface smooth and dull, sorediate. Soredia scattered, somewhat immersed 0.2–0.25 mm diam. Apothecia verruciform, rare, when present, scattered, rarely confluent, concolorous with thallus, slightly flattened, hemispherical, becoming constricted at base, 0.5–1 mm diam.; ostioles inconspicuous, pale to dark yellowish brown, 1 per verruca. Ascospores 8 per ascus, irregularly uniseriate, ellipsoidal, rarely subfusiform, smooth, 50–75(–90) × 25–37 μm.
Chemistry : K−, KC+ orange, C+ orange, Pd− or + weak yellow; containing thiophaninic acid (major), 2-chloro-6- O -methylnorlichexanthone (tr.), 4-chloro-6- O -methylnorlichexanthone (tr.), stictic acid (major), constictic acid (minor), ±lichexanthone (minor-tr.), rarely with additional norstictic acid (minor) (Elix et al. 1978b – as P. persulphurata; Archer & Elix 1993b: 114; Archer 1997: 167–168).
N: Northland (Hen I., Chicken I., Great Barrier I., Little Barrier I., Great Mercury I.). On coastal rocks. Also in E Australia from Queensland to New South Wales, Lord Howe I., Norfolk I, and Papua New Guinea (Archer 1991b, 1997, 2004a: 170; Archer & Elix 1993b; McCarthy 2003c, 2006).
Australasian
Illustrations : Archer (1997: 123, fig. 41); Flora of Australia56A (2004: 106, pl. 55).
Pertusaria xanthoplaca is characterised by: the saxicolous (coastal rocks) habit; the yellow, sorediate thallus, and the presence of thiophaninic and stictic acids. Earlier records of P. persulphurata from New Zealand (Archer & Elix 1993: 113; Malcolm & Galloway 1997: 32) are referable to P. xanthoplaca (Archer 1997:167).
