S MEMOIRS FROM TflE DEPARTMENT OF BOTANY OF COLUMBIA COLLEGE. 



GEOGRAPHIC DISTRIBUTION. 



The genus as a whole has a wide distribution, ranging from the tropics to the polar 

 regions, and from the level of the sea to the highest altitudes at which floAvering plants 

 can withstand the rigorous environment characteristic of such regions. 



The genus divides itself into a number of very natural sections, and we notice a char- 

 acteristic distribution by subgenera. Thus Bistorta is typically arctic, while Aconogonon 

 is normally alpine. The subgenus Tiniaria is north temperate in its distribution, Duravia 

 is C'alifornian, Tephis is South African, and Cephalophilon is confined to southern Asia, 

 (^ther sections as Persicaria, Avicularia, Amblygonon and Echinocaulon are tropical, tem- 

 perate and arctic in their range. 



There are probably some two hundred and fifty living species ; of these about ninety 

 occur in the western and one hundred and sixty in the eastern hemisphere. Seventy are 

 now known to exist in North America, and about thirty species are recorded for South 

 America, and there are forty-two peculiar to the former region, while only fifteen are at 

 the present time known to be endemic in the latter. 



THE GENERAL MORPHOLOGY. 



During the latter part of this century the genus has been accepted in about the same 

 way that Linnaeus understood it when he wrote the Species Plantarum. His contem- 

 poraries, however, and the botanists for some years after his time, held quite different 

 views as to its limits. At one time or another the genus as we now understand it has been 

 divided into as many as eight or ten genera. Adanson, ^ for instance, founded a genus 

 Tephia on a South African plant. The Polygonum of Tournefort was represented by those 

 plants which Meisner^ included under his section Avicularia and Avhich were embraced by 

 the genus Centinodia of J. Bauhin.^ A second genus of Tournefort was Persicaria, which 

 is about the same as Adanson's later Tovara* and Rafinesque's Antenoron.^' Loureiro de- 

 scribed a genus Lagunea,^ which is the same as Meisner's section Amblygonon, and a third 

 genus of Tournefort was Bistorta, which has also fallen to subgeneric rank. Chylocalyx of 

 Hasskarl," noAV standing as subgenus Echinocaulon of Meisner, and the latter's Tiniaria, 

 representing Dumortier's Bildcrdykia,^ have stood at one time or another in generic rank. 



So Polygonum has had a varied history, but of late all these divisions have been 

 brought under one generic head and retained there as sections or subgenera. Although 

 commonly accepted in this Avay, there has been more or less discussion concerning the 



1 Fam. PI. 2 : 276. < Fam. PI. 2 : 376. ' Beibl. 2 : 30. 



2Monog. 43 and 85. ^pi. Ludov. 38. ^Fl. Belg. Prodr. 18. 



3 Hist. 3 : 374. « Fl. Coch, 1 : 271. 



