106 CALIFORNIA ACADEMY OF SCIENCES. 



CONTRIBUTIONS FROM THE SHAW SCHOOL OF BOTANY. 



No. 4. 



synoptical list of north american species of ceanothus. 

 By William Trelease. 



In its present limitation, Ceanothus is an exclusively Amer- 

 ican genus, and all but three of the species known to me 

 occur north of Mexico, It is quite puzzling to the student 

 of our flora, partly because of the variability of some spe- 

 cies, and partly because in some instances what are evi- 

 dently distinct species approach each other so closely as to 

 render their characterization difficult, although they may be 

 pretty surely recognized by the practiced eye. To the evo- 

 lutionist, these groups of interlocking sub-species and 

 barely distinguishable species, are interesting as represent- 

 ing different stages in the mutations of their prototypes; but 

 they are exceedingly trying to the systematic botanist, 

 whose task is to so arrange and limit them as to render 

 their recognition by others easy. 



Aside from the monograph of the genus (in the broader 

 sense in which it was formerly understood) in De Candolle's 

 Prodromus, which characterizes very few of the species that 

 are now known, and the fuller revision in the first volume of 

 Torrey and Gray's Flora, it has been very judiciously and 

 completely treated by Mr. Watson in a revision of the en- 

 tire group (Proc. Amer. Acad. x. 1875, 333-9), and a separate 

 elaboration of the numerous and difficult Californian species 

 (Bot. Cal. i. 102-104; ii. 439). His views on the syno- 

 nymy of species are also very fully indicated in his Biblio- 

 graphical Index to North American Botany. Nor should 

 the field notes of the keen-sighted Nuttall, on a number of 

 the Pacific Coast species, in Torrey and Gray's Flora, be 

 overlooked. 



2d See. Vol. 1. Issued June 15, 1888. 



