CONTRIBUTIONS FROM THE GRAY HERBARIUM OF HARVARD 

 UNIVERSITY.— NEW SERIES, No. XLII. 



Presented by B. L. Robinson, May 14, 1913. Received June 24, 1913. 



I. A GENERIC KEY TO THE COMPOSITAE-EUPATORIEAE. 

 By B. L. Robinson. 



It is now more than twenty years since the genera of the Eupatoriuyn 

 tribe were keyed by Hoffmann in Engl. & Prantl, Nat. Pflanzenf. iv. 

 Ab. 5 (1890). During this interval several genera have been added 

 to the tribe, some few have been definitely removed from it to other 

 tribes of the Compositae, two (Brachyandra and Addisonia) have been 

 reduced, and certain sections of genera have come to appear worthy 

 of generic rank within the tribe. In consequence the key of Hoffmann, 

 though excellent for its time, is now unsatisfactory and far from com- 

 plete. The one here offered, though drawn up after some years' 

 study of the group, is put forth rather as a convenient working hy- 

 pothesis than a finished or monographic product. 



In the Eupatorium tribe, as elsewhere in the Compositae, generic 

 distinctions, though essential for classification, often seem pretty arti- 

 ficial and the more precisely they are stated the greater of necessity 

 becomes the artificial or arbitrary element. A re-examination of the 

 technical characters relied upon by the older authors discloses many 

 exceptions and transitions. On the other hand persistent attempts 

 to secure a more natural classification by relying in larger measure 

 upon habital traits have proved even more disappointing. These, 

 while fairly convincing among plants of a circumscribed area, quickly 

 lose any statable definiteness in dealing with the species of the world. 

 One is in consequence forced to a restatement of the distinctions of 

 pappus, achenes, anther-tips, and involucral-bracts as yielding after 

 all the most practical basis for classification in the group. 



In order to employ these more technical features effectively some 

 explanation and definitions are necessary. 



The pappus of the Eupatorium tribe offers a wide variety, including 

 nearly all forms found in the Compositae, Scales, distinct or connate, 



