A REVISION OF THE NORTH AMERICAN SPECIES OF THE 



SECTION BORAPHILA ENGLER OF THE GENUS 



SAXIFRAGA (TOURN) L/ 



Arthur Monrad Johnson 

 (With Plates I-XIX) 



The section Boraphila was established by Engler (4) in his Index 

 Criticus Specierum atque Synonymorum Generis Saxifraga and was founded 

 on those species of the genus Saxifraga (Tourn) L. which Tausch (30) 

 and later writers of the early part of the nineteenth century had grouped 

 under the sections Arahisa (Arabidia Seringe), Micranthes, and Hydatica. 

 In his later Monographie der Gattung Sagifraga Engler (5) retains the 

 classification as first set forth in the Index, and except for the enlargement 

 of the scope of the section the fundamental principles of this classification 

 are adopted in the more recent treatment in Engler and Prantl (6) t)ie 

 Naturlichen Pflanzenfamilien. 



In these studies the attempt will be made to show that the section 

 Boraphila as Engler persisted in construing it is a heterogeneous one, con- 

 sisting of species of widely different affinities, but which, however, can be 

 realigned into natural groups on the basis of certain fundamental characters. 

 Engler himself was not unconscious of a certain amount of heterogeneity 

 in his section, however, for in his Monographie (p. 127) he makes this 

 statement : "Allerdings weichen die Artengruppen, welche ich unter der sec- 

 tion Boraphila zussammenfasse, mehr von einander ab, als die Artengruppen 

 anderer Sectionen . . . . " Nevertheless he grouped them all in the one sec- 

 tion rather than make a number of new sections based on minor characters 

 ("geringfugige Merkmale"). 



In the Monographie Engler separates the section Boraphila on the shape 



«^ of the capsules and on their mode of dehiscence. But as far as these charac- 



o^ ters are concerned his section Rohertsonia is scarcely to be distinguished 



^'"^ from certain species of Boraphila (namely those of the section Arabisd). 



And again the "capsule" of Peltiphyllum is scarcely distinguishable from 



capsules of certain other species of Boraphila (for example, in Saxifraga 



oregana of the section Micranthes) . 



. ?5 In Die Natiirlichen Pflanseniamilien Engler includes in the section 



a: ^oBoraphila the genera Spatularia, Micranthes, Dermasea, and Aulaxis of 



g 'Ha WORTH, Dermasea of Hoppe, and the sections Arahisa and Micranthes of 



™' ^ Tausch. No attention is given in the classification to the characters of the 



-St „' 



* A tbesis submitted to the faculty of the Graduate School of the University of Minnesota in 



[jartial fulfillment of the requirements for the degree of Doctor of Philosophy. 



