The Species of Peltigera of North America North of Mexico

Thomson, John

In this paper I have attempted to treat in monographic form those species of the lichen genus P. eltigera which occur in North America north of Mexico. The study is based upon the collections in the major herbaria of the United States. Access to as many authentic and type specimens as was possible during the circumstances was sought. The conditions imposed by the second World War naturally cut off access to the European herbaria and made their impress upon the course of the work. Fortunately the collections at the Farlow Herbarium and Yale University contained many specimens determined by V. Gyelnik so that the numerous names proposed by this recent worker could be evaluated in the light of American material. As is only natural, there are disagreements over species limitations and I have followed a concept of broader limits than those expressed by this monographer in the numerous papers which he has published in preparation of a monograph of the Peltigeras of the world. Sufficient criticism of his too finely drawn distinctions has already been voiced in many papers of other lichenologists; my own disposition of many of his proposed names may be traced in the synonymy. Although Zahlbruckner has proposed conservation of the name Peltigera, citing the name as being proposed by Persoon in 1794, and antedated by Byrsalis of Necker in 1790, this is not necessary as the name was actually proposed by Willdenow in 1787 in Florae Berolinensis Prodromus. This contained the generally accepted type species P. canina (L.) Willd. The early authors included species now placed in Solorina, Nephroma, and even Sticta in their concept of Peltigera. Rabenhorst in 1845 emended the genus to include its present restricted sense. There have been proposals that the genus be divided into two, Peltidea and Peltigera, the divisions being based upon the presence of Chlorophyceae or Myxophyceae as algal constituents of the thallus. Aside from this one difference (and it is an inconstant one, the cephalodia of those whose algae are Chlorophyceae contain Nostoc) the great uniformity of structure through the various species of this highly organized lichen makes it difficult to agree with those who would make the division.

The Species of Peltigera of North America North of Mexico

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