RYDBERG: NoTES ON ROSACEAE Sit 
Even if there were no structural differences in the flowers of Ar- 
gentina and Potentilla (which, however, exist), there are not even 
any essential habitual differences between P. canadensis, P. sim- 
plex, and P. pumila on one hand, and P. reptans, P. procumbens, 
and P. Tormentilla on the other. 
Dactylophyllum Spenner* was a merging of Potentilla, Fragaria, 
Sibbaldia, etc., without any real type. 
The types of Chamaephyton, Dynamidium, and Hypargyreum 
Fourr.t are Potentilla supina L., P. verna L., and P. argentea Li 
respectively. Fourrier also proposed several other genera, of 
which Drymocallis was adopted by me for P. rupestris, P. glan- 
dulosa, and their allies. The rest of Fourrier’s genera are not 
represented by American species. Whether they should be re- 
garded as distinct genera or not, can be decided only by further 
study, and was out of the scope of the North American Flora. 
The monotype of Potentillopsis Opiz is Potentilla pentandra 
Engelm. 
Tridophyllum Necker{ has no type. It was based on the 
trifoliolate species of Potentilla L., of what book of Linnaeus 
Necker does not state under Tridophyllum; but on page 94 we 
find that he had in mind the 14th edition of the Systema. This 
mattered little, however, in this case, because this division of 
Potentilla remained unchanged from the first edition of the Species 
Plantarum to the 14th edition of the Systema, the first and the 
last of the works of Linnaeus that Necker possibly could have had. 
The group contained P. monspeliensis, P. norvegica, P. nivea, 
P. grandiflora, and P. subacaulis. Only the two first belong to 
Tridophyllum, as modified by Dr. Greene.§ He states: ‘““Among 
all segregated genera that have been proposed, not one is better 
entitled to the rank of a genus than Necker'’s Tridophyllum. As 
its name indicates, it is founded upon species of Linnaean Poten- 
tilla having trifoliate leaves. But this mark of the foliage is not 
one which is considered essential. He makes the generic rank 
of the group to rest on the very small ovaries, greatly reduced 
styles and minute naked achenes. The so-called Potentillas that 
*Fl. Frib. 1084. 1829. 
yAnn. Soc. Linn. Lyon II. 16: 371. 1868. 
tElem. 2: 93. 1790. 
§Leaflets 1: 188. 1905. 
