American ferns— VI. Species added to the flora of the United 



States from 1900 to 1905 



Lucien Marcus Underwood 



Since the beginning of the serious study of our native ferns, 

 there has probably been no similar period in which so many addi- 

 tions have been made to our flora as in the five years just passed. 

 This has been due to several causes, the most important of which 

 is the opening up to exploration of the really tropical portion of 

 southern Florida, with the consequent addition of a large number 

 of species mostly more or less common in the lowlands of the 

 Bahamas and the Antilles. Some of the additions are due to the 

 closer analysis which has been given in recent years to certain 

 genera, particularly Selaginella by Professor Georg Hieronymus, 

 hoetes by Mr. A. A. Eaton, and Botrychium by the present writer. 

 The proper delimitation of certain species of central and southern 

 Florida has depended on special conditions. For example, while 

 the writer was collecting in Florida during the winter of 1890-91, 

 two species already known from that state were found growing to- 

 gether in similar situations on limestone rocks. Although these 

 ferns had been referred, the one to a West Indian species and the 

 other to a variety of the same, on collecting these species fifteen 

 years ago the writer felt as fully as he does now (1) that the two 

 had full specific distinctness, and (2) that the places to which they 

 had been assigned by the •'authorities" was not the correct one. 

 Two essential conditions, however, were then lacking to justify their 

 separation, and the writer has waited until these conditions might 



be changed : 



1. It was essential for accuracy to make examination of certain 

 types in European herbaria; this has not been practicable until the 



past summer ; and 



2. It was necessary to study a large collection of West Indian 

 species of Asplenimn in order to delimit the boundaries of related 

 species. This has now become possible at home, for while the 

 Kew herbarium and the Berlin collections, including the well 



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