378 Rydberg : Notes on Rosaceae 



evince these characters have other marks more obvious. Their 

 roots are annual, or now and then of biennial duration. All other 

 plants that ever were referred to Potent ilia are perennial, and 

 very many stiff rutescent." So far, Dr. Greene. Let us see of 

 what value these characters are. Potentilla nivea, P. grandiflora, 

 and P. subacaulis, also trifoliolate species of the Linnaean Poten- 

 tilla, and hence part of Tridophyllum Necker, do not fulfill this 

 characterization. Some may claim that they did not constitute 

 a part of Necker's genus, but why not? Necker placed the pinnate- 

 leaved species in Potentilla, the trifoliolate ones in Tridophyllum, 

 and the digitate-leaved ones with more than three leaflets he 

 transferred to Tormentilla. In a note under Tormentilla he states 

 that 5 species of Potentilla are to be referred to Tridophyllum; 

 hence the five given above, of which P. subacaulis has very long 

 styles and the other two have rather large achenes. They are all 

 three perennials. 



But is Tridophyllum as modified by Greene a well-defined 

 genus? Potentilla intermedia and P. heterosepala have both the 

 very short styles and numerous small achenes, and are both in- 

 cluded in the Supinae group by Dr. Wolf, the world-authority 

 on Potentilla; but they are both perennials. The former is very 

 close in habit to P. monspeliensis, which occasionally is a short- 

 lived perennial. Potentilla Newberryi has all the character of 

 that group, but the style is long. The short style, often glandular 

 at the base, and the numerous small achenes, characteristic of the 

 Supinae group, are found in many other Potentillas, especially 

 of the Multifidae group. These characters are worth little as 

 generic characters. 



While vol. 25, part 4, of the North American Flora was going 

 through the press, we received at the New York Botanical Garden 

 the excellent monograph of the genus Potentilla by Dr. Theodor 

 Wolf.* If this valuable work had reached us a little earlier, some 

 changes and corrections might have been made in my monograph , 

 and quite a number of synonyms could have been added. The 

 monographing of the whole genus, for the whole world, is a stu- 

 pendous undertaking. Dr. Wolf's work is one of the most elab- 

 orate, conscientious, and critical ever published. It is a large 



*Bibliotheca Botanica, Heft 71. 



