4 



Preliminary notes on the genus Usnea, as represented In 



New England 



m 



R. Heber Howe, Jr, 



(WITH PLATES 21-23) 



There is probably no small genus of Lichenes that seems more 

 puzzling to the student than the genus Usnea, nor one over which 

 lichenologists are more uncertain or have more often disagreed. 

 We have only to follow the literature from Linnaeus to Tucker- 

 man to see how the status of the species has been continually 

 rearranged, though the genus, so far as I can ascertain, has been 

 monographed but once, in 1799,* 



A long study of the plants of this genus in the field, with the 

 assembling of a large collection of specimens, and a comparison 

 of over two thousand examples in other herbaria, has led me to 

 believe that the members of the genus are often determined by a 

 most superficial examination, and that one of the best criteria of 

 Tuckerman's Genera Lichenum (p. 13) — papillate or epapillate 

 thallus — is left out of the equation in the majority of cases where it 

 could have been applied. I have found numerous instances where 

 examples with a glabrous \i}s\-dX\\xs have been placed under barbata^^ 

 and distinctly papillate species labelled both trichodea and longis- 

 sima. Superficial comparison is used so generally for the deter- 

 mination of lichens that one specimen, wrongly determined, may 

 be the highway for many more. 



The general infertility of the filamentous forms, the wide 

 variety of color, which is greatly affected by age, both during 

 growth and in herbaria, have also helped to lead to the common 

 dilemma. 



That in some ways the genus would be more easily understood 

 if revised,! there seems little, doubt, though the less we tamper 

 with the only American standard to which we can cling, the bet- 



*Schrader, H. A. Jour, ftir Bot. i : 42-85, including Alectoria, 



f See conclusion of paper. 



4: See Zahlbruckner in Engler & PrantI, Nat. Pflanzenfam. 



309 



