INTRODUCTION^. 



The genus Polygonum is the type of the natural family Polygonaceae. This 

 family of dicotyledonous spermatophyta has no very close affinity to other groups, and 

 authors do not differ, to any great degree, as to the relative position of the family. 



Among the writers who have arranged groups in a linear sequence, Meisner^ placed 

 the Polygon ACE AE between Petiveriaceae and Eeiogojsteae ; Endlicher^ brought them 

 in between Amaranth aceae and Nyctagineae, Bentham and Hooker^ between the 

 Batideae and the Podostomaceae. Lately Greene* has placed the family between 

 Illecebreae and Nyctagineae.- These different groupiiigs are practically the same and 

 logical as far as the system permits. Baillon,^ of all the writers ori genera, seems to have 

 made the most illogical disposition of the family in placing it between Plumbaginaceae 

 and JuGLANDACEAE. On the other hand, Engler aiid Praiitl,^ working out their system 

 on the divergent lines of the descent of groups,' place PolygoNaceae at the beginning 

 of one of their lines, and follow with the family ' Chenopodiaceae. The limits of the 

 family have with few exceptions been accepted in abotit the same way. Dumortier,' in 

 1829, transferred the g«nus Efiogonum to the Chenopodiaceae, making it there the type 

 of a tribe. Meisner* some years later removed the genus from that family and raised it 

 to ordinal rank, founding a fanlily on it as a type, arid including under it the poly- 

 gonaceous genera Pterostegia, Mucronea and Chorizanthe. 



The family, as understood by me embraces some seven hundred species, which fall 

 into about thirty-five natural genera, some of which are mbnotypic, while others include 

 numerous species.- It is distributed throughout the globe, being well represented in the 

 tropical, the temperate and the arctic regions. ' The greater number of species occur, how-" 

 ever, in the Northern Hemisphere. There are a few interesting points concerning the 

 geographical distribution of the genera. In the first place, there are those with a re- 

 stricted area of distribution and others which are .general throughout. We find Macounia 

 {Koenigia L., not Adans.) confined to a circumboreal zone and to the higher parts of the 

 Himalayas with a corresponding temperature, while such genera as Coccoloba, Symmeria 



iPl. Vas. 6en.:228. ■> Fl. Francis. 133. 'Anal. Fain. 17. 



2 Gen. PI. 304. . s Hist. des. PI. 367. spi. Vas. Gen. 339. 



3 Gen. PI. 3 : 88. * Nat. Pfl. Fam. 3 : Abt. la, 1. 



