406 Rydberg : Notes on Rosaceae 



horkeliella 

 The writer thought it advisable to raise the subgenus Horkeliella 

 of Horkelia to generic rank. Even if the characters separating it 

 from Horkelia and Ivesia are not very prominent ones, the writer's 

 opinion is that the arrangement here adopted will make the treat- 

 ment of the tribe much clearer. To the two species included in 

 the subgenus is to be added a third one, Horkelia Congdonis. 



Ivesia 



The writer restored this genus in the North American Flora, 

 after having included it in Horkelia in his Monograph of the North 

 American Potentilleae. In the latter publication he reduced it, 

 simply because one species, /. argyrocoina, has more or less dilated 

 filaments. The species is in every other respect as good a species 

 of Ivesia as any of the /. iingiiiculata group. The type species of the 

 genus, /. Gordonii, has but 5 stamens and a more scape-like stem, 

 but the structure of the flower and the general habit are otherwise 

 practically the same. In /. pygmaea, I. Shockleyi, T. setosa, and 

 S. Baileyi, the hypanthium is much flatter than usual in the genus; 

 it has a distinct thickening or disk in the throat, and the filaments 

 are short, inclined towards the center of the flower, thus approach- 

 ing the structure of the flowers of the genus Comarella. These 

 species (except sometimes the last one) have leaves with spinulose- 

 tipped teeth or lobes, and only 5 stamens. It is not advisable to 

 remove these species from Ivesia, however, for at least the first two 

 have otherwise the habit of /. Gordonii and other 5-stamened 

 species of the /. lycopodioides group ; and another species, /. chaeto- 

 phora Rydb., has the same habit and the same spinulose-tipped 

 teeth or divisions, but a more campanulated hypanthium, no thick- 

 ened disk, and 10 stamens. 



The species of the /. eremica group approach the genus Poten- 

 tilla in the almost clawless petals and the less developed hypan- 

 thium, but otherwise they are typical Ivesias. 



The following species were proposed as new : /. Tivccdyi, I 

 viegalopetala, and /. setosa. 



The first one was included in Hoj^kelia utahensis in my Mono- 

 graph ; the other two were there treated as varieties of H. Gor- 

 donii and H. Baileyi, respectively. 



