1921] St. John,— Critical Revision of Hydrangea arborescens 203 



mation of other collections, either in the field or from herbaria, with 

 data which may verify not only its occurrence here hut may deter- 

 mine its status as indigenous or as "cultivated and escaped east- 

 ward." 



I )ORCHE8TER, MASSACHUSETTS. 



A CRITICAL REVISION OF HYDRANGEA ARBORESCENS. 



Harold St. John. 



Through the discriminating field observations of Mr. Charles C 

 Deam, the writer has had his attention directed to the conspicuously 

 different plants that are now treated as Hydrangea arborescens L. 

 The tendency of the present day authors is to withhold any recogni- 

 tion of these various forms. On the other hand, the writers of the 

 early floras of eastern North America were familiar with some of 

 them and gave them names. Rafinesque, for instance, made eight 

 species out of the plant now considered to he //. arborescens. The 

 others were more conservative. As was the case in a previous study 

 of the variations of a polymorphic species, 1 a treatment very similar 

 to that here presented is found in Torrey and Gray's Flora of North 

 America. Within the species itself are recognized several subdivi- 

 sions, which in most cases are clearly distinguishable by definite 

 characters and by having different ranges, but they are shown to 

 be of less than specific value by the existence of specimens having 

 intermediate characters, and by the fact that their ranges overlap. 



Linnaeus in founding //. arborescens 1 based it solely on HYDRAN- 

 GEA. Anonymos Horibus albis parvis, etc. of Gronovius. 3 This 

 description was drawn from the Clayton specimen, no. 7!>, from 

 Virginia. It is a low shrub with large cordate acuminate glabrous 

 leaves. By using a hand lens it appears that the leaves of this shrub 

 of the stream-banks of Virginia are essentially but not absolutely 

 glabrous, for the principal nerves bear on the lower surface a short 

 puberulence. This same character holds throughout the species 

 and its varieties; in all cases the leaves are puberulent on the prin- 



1 Lalhyrus venoms Muhl., see Butters and St. John, Rhodora xix. 15(5 (1917). 



2 Sp. PI. i. 397 (1753). 



3 FT Virginica i. 50 (1739). 



