1955] 



REVISION OF THE GENUS SAGITTARIA 



185 



Taxa 



Chromosome numbers in Sagittaria 

 n 



S. cuneata (as S. ari folia) 

 S. engelmanniana 



subsp. engelmanniana 



subsp. longirostra 

 (as S. longirostra) 

 S. graminea var. graminea 



var. teres (as S. teres) 



var. weatherbiana (as 

 5". weatherbiana) 

 S. land folia 



subsp. lancifolia 



subsp. media (as 

 S. f ale at a) 

 S. lati folia var. latifolia 



var. pubescens (as S. pubescens) 

 S. montevidensis 



subsp. montevidensis 

 S. rigid a 

 S. sagittifolia 



S. agin as hi 

 S. natans 

 S. tri folia var. sinensis 



S. subulata var. gracillima 



var. kurziana (as S, Kurziana) 

 var. subulata 



11 



ir 



11* (Oleson, 1941) 

 11* 



11 



11 



2n 



22* (Brown 1947) 

 22 (Brown 1947) 



22 

 22' 

 22 



(Brown 1947) 

 (Brown 1947) 

 (Brown 1947) 



IT 



22 (Brown 1947) 



22 (Brown 1947) 



22 (Brown 1947) 

 22* (Oleson 1941) 

 22* (Brown 1947) 



ca. 20 (Taylor 1925) 

 22* (Oleson 1941) 

 22 (Lohammer 1931) 

 16 (Liehr 1916) 

 22 (Shinke 1929) 

 22 (Lohammer 1931) 

 22 (Morinaga and 



Fukushima 1931) 

 20 (Nawa 1928) 

 ca. 44* 



22 (Brown 1947) 

 22* (Brown 1947) 



Cytological work is still far from complete, for 20 of the 36 taxa here main- 

 tained have not as yet been investigated. On the basis of the known counts it 

 may be stated that in Sagittaria polyploidy or aneuploidy do not seem to play any 

 considerable role in speciation. 



DEVELOPMENTAL TRENDS 



The relationships between species of Sagittaria are discussed in greater de- 

 tail in the systematic treatment that follows; however, the developmental trends 

 within the genus present an interesting correlation with their geographic 

 distribution. 



Any phyiogenetic discussion is at best speculative. Nevertheless, the vast 

 amount of material examined by the writer and his final disposition of taxa lead 

 inevitably to some conclusions, which, while they cannot be absolutely verified, 

 seem correct and follow the accepted dicta of plant geography. In the course of 

 this investigation it was noted that the genus can be separated more or less nat- 

 urally into two subgenera. The subgenus Lophotocarpus, predominantly tropical 

 and warm-temperate in distribution, is characterized by pistillate flowers on re- 

 curved thickened pedicels and with appressed to spreading sepals, besides having 

 some species characteristically with perfect flowers in the lower whorls. The 

 subgenus Sagittaria, predominantly north-temperate in distribution, is characterized 

 by pistillate flowers on ascending, non-thickened pedicels and with sepals re- 

 flexed, while the presence of perfect flowers is sporadic. Interestingly enough, in 

 both subgenera the species with intermediate characteristics occupy intermediate 

 geographical ranges. 



