Since the monographic treatment of the lichen genus Leioderma Nyl. (Galloway & Jørgensen Reference Galloway and Jørgensen1987), the sorediate species, L. sorediatum, described there, has not unexpectedly proven to have a wider distribution. It was recently reported from peninsular Malaysia (Jørgensen Reference Jørgensen2005). Since it occurs much further north in insular SE Asia and the Pacific region (Jørgensen Reference Jørgensen1994) there has been reason to believe that it may be more widespread in mainland Asia.

Indeed, it was discovered among material collected by the second author and coworkers in Thailand and provisionally filed as Erioderma sorediatum. Leioderma sorediatum often grows with E. sorediatum also found in Thailand (Wolseley et al. Reference Wolseley, Aguirre-Hudson and McCarthy2002). The two species are often confused but easily separated by the PD reaction which is orange in E. sorediatum and negative in L. sorediatum (see Jørgensen Reference Jørgensen1994). It has also been found among material collected by Sureporn Jariangpraset from the same province (BG).

The first author also supposed that the record of Erioderma mollissimum, the mainly subtropical American species (Arvidsson & Jørgensen 2001), in the netversion of the checklist of lichens in Thailand (RAMK) might be based on browned specimens of Leioderma sorediatum. This has been confirmed by examination of herbarium material in RAMK. The latter has much narrower lobes and more granular, greyish soralia, while those of E. mollissimum, in spite of being PD−, contain an unusual lichen substance (wrigthin) not found in Leioderma, and are powdery and bluish.

We further suspect that the unlikely record of E. mollisimum from Alaska (Geiser et al. 1994) is based on a similar misunderstanding. Unfortunately, the specimen cannot be traced. The only known correct records of this species outside subtropical America are those from Atlantic Canada, Macaronesia, Portugal and East Africa, so that the map in Jørgensen & Arvidsson (Reference Jørgensen and Arvidsson2001) is basically correct except that the records from the Newfoundland region need to be added (P. M. Jørgensen, S. Clayden, J. A. Elix & C. Hanel, unpublished).

These discoveries reduce the number of known Erioderma species in Thailand to one, E. sorediatum, and add Leioderma sorediatum to the list of Thailand lichens. The latter may prove to have an even wider distribution in Indochina as it appears in evergreen, montane fagaceous forests in two widely different regions of Thailand at altitudes ranging from 1200–2450m, the latter being at an unusually high altitude compared with those in the diagram by Galloway & Jørgensen (Reference Galloway and Jørgensen1987), and almost similar to those at the Equator. However, Aptroot et al. (Reference Aptroot, Sparrius and Lai2002), record the species from Taiwan at 2250m (on relict mature trees of Shiia calesii), so it appears to have a wider altitudinal range than known previously.

Specimens studied of Leioderma sorediatum. Thailand: Chiang Mai: Doi Inthanon, roadside summit 42, alt. 2450m, 1993, James, Wolseley, & Svasti 2428(BM); Doi Suthep N.P., Sanku, alt. 1600 m, Wolseley 1476 (BM). Nakon Ratchasima: KhaoYai Natl. Park, Pha Trom Jai, Khao Kaiew, alt. 1200 m, 1999, C. Vongsripheug & S.Trangprasertsri RU-13376, RU-15495; ibid, C. Na Phuket RU-12669 (RAMK); Chud Chom view, Khao Kaiew, alt.1200m, 1999, K. Papong, RU-12212/13; ibid. 2001, W. Polyiam, RU-17906 (RAMK).