Rydberg: Phytogeographical notes 97 



parents as some existing circum polar-arctic plants. While one 

 offspring has remained arctic, i. e. has not spread south during the 

 glacial period or else has died out in the alpine regions, the other has 

 become both alpine and arctic with a purely American distribution, 

 or else the latter has developed from the former since glacial time. 

 Such plants are: 



North American arctic-alpine Circumpolar arctic 



Chrysosplenium tetrandrum C. alter nijolium 



Antennaria media A. alpina 



*Antennaria umbrinella A. alpina 



A few strictly arctic plants have for some reason spread into the 

 Rockies, their existence there being a little hard to explain. 

 Among these may be mentioned Phippsia algida, which has been 

 collected in one place in Colorado. It is otherwise not known 

 out of the arctic. Sagina nivalis has been found in Colorado; 

 otherwise only in the arctic regions of America and in the Scandi- 

 navian mountains. 



The following are truly endemic American arctic-alpine plants 

 without any close relatives as far as I know elsewhere: 



Ranunculus hyperboreus *Erigeron compositus and its close 



relatives, viz. 

 Aragallus podocarpus *Erigeron multifidus 



*Vaccinium caespitosum Erigeron trifidus 



The following are probably derived from subarctic or subalpine 

 species : 



*Calamagrostis Langsdorfii] C. canadensis, American, subalpine 



and boreal. 



*Alsine laeta A . longipes, American, subarctic, sub- 



alpine and boreal. 



*Kalmia microphylla K. glauca, eastern American, sub- 



arctic and boreal. 



*Senecio cymbalarioides S. aureus, eastern American, boreal. 



t This is also found in subarctic Scandinavia. 



