W illîin the very large genus of ferns Dryopteris, there is scarcely any group 

 of species so difficult to unravel as the numerous forms allied to D. opposita and 

 D. Spremjelii. Although several American species of that group were already descri- 

 bed at an earlier period, Bakeh in ''Synopsis Filicum" (^1874) enumerated and de- 

 scribed hardly more than 10 species, i)assing in silence a long series of forms that 

 older authors had considered to be good species. The consequence of this treat- 

 ment in this, the most important handbook of systematic pteridology, has been 

 that a greater part of these older, often good species have been forgotten or de- 

 scribed again under new names. "Synopsis Filicum", is therefore in this as in 

 many other points, partly to be blamed for the hitherto so chaotic synonymy of 

 the ferns. It will there be necessary to submit most of the genera of ferns to a new 

 and detailed revision, if we wish to succeed in getting a view of the difîerent forms 

 of ferns and of their geographical distribution. The material accumulated in the 

 museums during recent years has been so considerably increased and the descrip- 

 tive pteridological literature has grown to such an extent, without parallel perhaps 

 in the whole botanical literature, the number of species described as new in 

 recent years running up to more than half of the complete number of species in 

 "Synopsis Filicum" (for instance in one year 1906 over 300 species were described), 

 that it will be quite beyond the capacity of one man to prepare a modern "Synop- 

 sis". It is a work which must necessarily be distributed over many hands, and in 

 recent times much has already been done. Not only have single groups been 

 revised, for instance by Christ (Elaphoglossum), Lindman (üidymoglossum), Under- 

 wood (Danaea, Stenochlaena and others), Hieronymus (a group of Polypodiiim) and 

 by myself (Leptochihis), but the fern floras of some countries have also been criti- 

 cally dealt with by Christ, Hieronymus, Rosenstock and others. My work here 

 is intended to be a link in the work of gaining a clearer and more modern idea 

 of the classification and distribution of the ferns. 



When preparing my "Index Filicum" I never felt how complicated the 

 synonymy may be more than during the elaboration of the genus Dryopteris, and 

 it became evident to me that something had to be done as soon as possible to 

 unravel the chaos of names, which I found myself to a great extent compelled to 

 refer as synonyms to the few species accepted in the "Synopsis Filicum". Slill 



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