The Genus Parmeliopsis of Nylander

Abstract

(With Plate XX) The writer's interest in the group of lichens to be discussed in this paper was first aroused by collecting from an old fence in Needham, Massachusetts, a small, gray, foliose lichen, densely covered with isidia, and suggesting Parmelia rudecta Ach., but lacking the white punctations of that species. In subsequent collecting the lichen was found to grow also on the bark of pines, and proved to be common in Massachusetts, although apparently not much collected. A comparison with material in the Tuckerman Herbarium showed that the plant was what he had called Cetraria aleurites (Ach.) Th. Fr. But when the European authorities were consulted, it was found that there was much confusion in their interpretation of the Lichen aleurites of Acharius. Visits to the leading European herbaria in 1912-1913, including the original herbarium of Acharius now in the Botanical Museum at Helsingfors, gave an opportunity to study first hand the problem of Lichen aleurites and its allies. These lichens have been known by American students under the names used in Tuckerman's Synopsis of North American Lichens: Cetraria aleurites, Cetraria aleurites var. placorodia, Parmelia amnbigua, and Parmelia ambigua var. albescens. Tuckerman thus considered two of these to be varieties of the other