PROCEEDINGS 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. VIII, pp. 167-196. December 18, 1906. 



A STUDY OF RHUS GLABRA. 

 By Edward L. Greene. 



INTRODUCTION. 



The genus Rhus as Tournefort restricted it two centuries ago, 

 and as many another systematist since his day has held it, is 

 clearly marked and easily denned. As to habit — that foremost 

 indication of a good plant genus — this generic type stands well 

 aloof from all its allies ; even distinctly apart from each and 

 every one of those kindred generic groups which, like Cottnus, 

 Toxicodendron, Metofiium, Lobadium, Rhoeidium, and Styftho- 

 nia, in another than the Tournefortian school of taxonomy, have 

 been thought of as preferably constituting mere subgenera of 

 RInts. But not a species in any of those other genera named 

 makes the least approach to typical Rhus in habit. Every species 

 and variety of this appears as a shrub or tree with few stout stag- 

 horn-like branches, each clothed heavily near its summit with 

 odd-pinnate leaves, these usually large and of many leaflets. 

 In our silva the only tree which in aspect recalls the sumachs is 

 that naturalized alien, the Ailanthus, a genus 01 no near affinity 

 to Rhus. But between the last and its near relative Schmaltzia 

 there is no habital resemblance. In this regard they are quite 

 as unlike as are currant bushes and elder trees ; and, as for 

 Toxicodendron, its habit is as remote from that of Rhus as the 

 habit of a grape vine or English ivy is remote from that of wal- 

 nut trees. 



Over and above its marked habit, the characters by which this 

 Rhus of Tournefort establishes itself as a model genus are, the 

 Proc. Wash. Acad. Sci., December, 1906. 167 



