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Erioderma mollissimum is a rare cyanolichen found on the foggy Atlantic coast of Canada. The rarity of E. mollissimum and the potential threat from human impact has led to conservation concern for this species in Canada. Recent finds on the island of Newfoundland suggest that the distribution of E. mollissimum may be wider than historically known. In order to better understand the environmental factors affecting distribution and to direct future search efforts a Mahalanobis predictive distribution model using a geographical information system (GIS) was developed for Atlantic Canada. The model suggests that only a small part of this region is suitable for E. mollissimum. This study provides an example of an alternative modeling technique to the traditional statistical methods for predicting lichen distribution.

Well-developed thalli of Erioderma mollissimum have been found on the island of Newfoundland. Previously reported collections from other areas of Atlantic Canada, and from high elevations in the southern Appalachians, were small and poorly developed. It had been suggested that these might represent a distinct, undescribed species. However, the morphology and chemistry of the collections reported here confirm the identity of the Newfoundland population as E. mollissimum.

The lichen genus Erioderma is shown to be particularly species-rich in Ecuador, especially in the upper cloud forest (3000–3400m). Altogether seventeen species are recorded of which the following are new: E. barbellatum, E. cyathophorum, E. divisum, E. gloriosum, E. papyraceum, E. pycnidiferum, E. sinuatum, most of which also occur in the neighbouring countries. Two further taxa from these are described as new: E. latilobatum from Bolivia and E. peruvianum from Peru and Bolivia.

Two new species are described: Erioderma glabrum (from the Antillean region and Ecuador) and Parmeliella conopleoides(from Brazil, Venezuela, and Costa Rica). Both species are unusual in their respective genera. Erioderma glabrum is the only glabrous species in the genus Erioderma, with no obvious close relations, while P. conopleoides is a species of the Parmeliella pannosa group and the first species in this genus known to have gymnidia.

For the three species of Erioderma occurring in North America (E. mollissimum (Samp.) Du Rietz, E. pedicellatum (Hue) P. M. Jorg. and E. sorediatun D. Gall. & P. M. Jorg), considerable range extensions are being reported together with ecological information that will help to understand the distribution of these lichens. Erioderma sorediatum has been recently discovered in North America by Sherwood and Pike (unpubl.), while E. mollissimum and E. pedicellatum are reported as new to Nova Scotia herein along with a number of new localities for the latter species in Newfoundland. Ongoing work on E. pedicellatum and its symbionts has been summarized and an attempt has been made to outline its possible postglacial history. It is postulated that the presently known ranges have been occupied by the lichen only within the past few thousand years (more recently in Europe than in North America), and that considerable migrations must have taken place prior to that. This is NRCC publication No. 20463.

The structure of eriodermin, a depsidone from the lichen Erioderma physcioides , has been established as 4-formyl-2,7-dichloro-3-hydroxy-8-methoxy- 1,6-dimethyldi-benzo[b,e][1,4]dioxepin-11-one by X-ray analysis.