LIST OF LICHENS OCCURRING IN THE UNITED 

 STATES. 



This list is by no means complete. It is, in fact, at 

 present impossible to give the exact number of species 

 occurring within the territory indicated. Willey be- 

 lieves that ultimately one thousand species will be 

 found. No authentic list can be compiled until the 

 existing species have been carefully determined. It is 

 very probable that a considerable number of lichens 

 have been described as distinct species which are in 

 reality one and the same species ; particularly is this 

 true of the lower forms. 



The list gives some idea of tho number of species 

 occurring in the various genera, and will be found of 

 great value to those who wish to make exchanges or 

 who wish to build up a fairly complete lichen-herba- 

 rium. 



The families are given in their natural order, while 

 the genera and species are given in alphabetical order. 

 This arrangement in alphabetical order is simply for 

 convenience of reference. The list gives about 1,250 

 species and varieties ; of these, no doubt a consider- 

 able number are synonyms. Furthermore, there are 

 a few doubtful genera and species which have been en- 

 tirely omitted. It is highly probable that there are 

 not more than 1,200 authentic species and varieties of 

 lichens in the United States. 



