1955} 



REVISION OF THE GENUS SAGITTARIA 



225 



tOi 100 ti 90 8» 60 »MT UNCtTMOI TS^ 



18 



FIG. 18. Distribution of S. engelmanniana, a-c, subsp. engelmanniana. a, achene, 

 X 3« b, bracts, x %, c, stamen, X 3. d, e, subsp. longirostrata. d, achene, X 3. e, bracts, 

 X % m f, g, subsp. brevirostra, f, achene, X 3. g, bracts, X 2 / 3 . 



engelmanniana, have been arbitrarily placed in subsp. longirostra solely on the 

 basis of range and ecology. 



Westward and northward subsp. longirostra is replaced by subsp. brevirostra. 

 This group is characterized by mostly branched scapes, large, non-echinate re- 

 ceptacles, and generally smaller achenes. Intermediates frequently occur along 

 the common border of this subspecies and subsp. longirostra, Subsp. brevirostra 

 apparently hybridizes with S. latifolia as discussed earlier. In the northwest portion 

 of its range it commonly occurs with 5. cuneata, and there is some evidence that 

 it has hybridized with that species. Indeed the shortened beak in subsp. brevirostra 

 and the branched scape of S. cuneata in this area may have resulted from hybridi- 

 zation and subsequent gene-flow from one population to the other. 



18. Sagittaria cuneata Sheldon, Bull. Torrey Club 20: 283. 1893. 



Sagittaria sagittifolia var. minor Pursh, Fl. Am. Sept. 2: 395. 1814. 

 Sagittaria variabilis var. hastata Macoun, Cat. Canad. PI. 4: 77, p.p. 1888. 



