Thallus: crustose, c. 4 cm across, rimose to areolate or scurfy-squamulose; prothallus: sometimes visible, thin and dark brown areoles: plane to uneven-warted or slightly verrucose, angular to +round, sometimes upturned at margin and often wavy, incised, rarely imbricate, 0.2-0.4(-0.7) mm wide, c. 0.3 mm thick, not lobulate at the margin surface: pale brown or gray-brown to yellowish brown, not discolored when wet, dull, epruinose; margin: concolorous with the center cortex: not differentiated, mostly ecorticate, occasionally paraplectenchymatous with cells 2-5 µm wide, without an epinecral layer medulla: with indiscernible hyphae; algal layer: with scattered algal cells 5-12 µm wide throughout the thallus Apothecia: frequent, broadly sessile or somewhat immersed, scattered, rarely grouped, 0.2-0.5 mm in diam. disc: red-brown to dark-brown, slightly paler (reddish brown) when wet, plane, sometimes weakly convex, epruinose margin: concolorous with the thallus, up to 0.1 mm wide, swollen when young, narrower when old, sometimes crenulate, not excluded amphithecium: outer edge anatomically similar to cortex of the thallus, with a colorless, superficial, amorphous layer, intermixed with photobiont cells, with algae filling the entire margin and abundant under the hypothecium parathecium: sometimes present, poorly developed, up to c. 20 µm wide at outer part, concolorous with the epihymenium epihymenium: brown, red-brown to orange, without granules, ±uniformly colored, K-, N- hymenium: hyaline, 6070 µm tall; paraphyses: simple to occasionally branched, c. 1.5 µm wide below, slightly swollen (clavate, up to c. 4 µm wide) and short-celled in the upper third and often with brown-black cell walls; hypothecium: hyaline, with unoriented hyphae, up to 150 µm thick in center including subhymenium asci: narrowly clavate, 40-50 x 12-20 µm, with a thin amyloid outer gelatinous coat, lacking an ocular chamber, Catillaria-type, 8-spored ascospores: hyaline, 1-septate, clavate to ovoid, (9-)10-14(-16) x 3-5 µm (in water), thin-walled, halonate; perispore: swelling up to c. 2 µm wide in K, often not well developed Pycnidia: occasionally present, inconspicuous, immersed in the thallus, 80-100 µm in diam., pale brown around the ostiole, hyaline below conidia: simple, short bacilliform, 3-4 x 1 µm Spot tests: K-, C-, KC-, P- Secondary metabolites: two unknown triterpenoids detected by TLC. Substrate and ecology: on acidic stones, including volcanic rock World distribution: Australia and North America Sonoran distribution: central and southeastern Arizona. Notes: Halecania australis is distinguished by its fine rimose to areolate thallus with occasionally small brown squamules, mostly sessile apothecia, halonate ascospores, including two unknown triterpenoids. In habitus, H. australis resembles Lecania rabenhorstii or L. inundata, and it resembles most of all Solenopsora "chihuahuana", especially by its squamule form. The latter species, not yet formally described, has rather similar paraphyses and asci, but the ascospores are not halonate. Moreover, the thallus of S. "chihuahuana" is not clearly areolate, not even partly so, as is the case in H. australis. Rather it is squamulose with relative large squamules. None of the other Halecania species known from acidic rocks have a pale brown thallus, that is partly squamulose. According to Lumbsch and Feige (1994), the thallus ofH. australis is adnate, continuous to areolate and contains atranorin (major), zeorin (major) and chloroatranorin (minor). However, re-examination of the holotype by Prof.J. Elix (personal communication) proved that it had two metabolites belonging to unknown triterpenes. Examination of additional specimens from Australia also showed that H. australis is a much more variable species than was initially recognized. The thallus in specimens from the type locality is adnate thin, continuous to areolate, but some Australian specimens have the same small squamulus, as found in the Sonoran material. Even the apothecia show great variability from adnate to more often clearly sessile or somewhat constricted at base in Australian material.The only Halecania species reported so far from the Pacific coast (Washington) is H. viridescens (Tønsberg 1994). Furthermore, examination of the holotype of the eastern North American species 'Lecania pepegospora', showed that it also belongs to Halecania. The thallus of 'L. pepegospora', which have been found on gneiss reacts P+ orange-red, consists of granular, clustered warts, similar but smaller than European species, such as H. alpivaga, that occurs on slightly calcareous rocks and reacts P-. Confusion of H. australis is possible with Lecania arizonica, an inland species superficially resembling it and occurring in northwestern and central Arizona. However, L. arizonica has clearly pruinose apothecia , verrucose warted areoles 0.3-1.5 mm across, and non-halonate ascospores. I am grateful to Dr Harrie Sipman for checking a Sonoran specimen with TLC, for an earlier version of the manuscript and for the loan of the isotype specimen of Halecania australis. I am also grateful to Prof. Jack Elix for studying the chemistry of the holotype of Halecania australis. Dr Roland Moberg is thanked for the loan of the holotype specimen of Lecania pepegospora; and Dr Walter Obermayer, for the loan of a lot of selected Halecania specimens from GZU.