HALORAGACEAE 



1. Flower parts in 4's; fruit a schizocarp, splitting into four 1-seeded 



nutlets (figs. 2-6); emersed leaves reduced, bracteate, less than 1 cm. 



long. 



1. Myriophyllum 



1, Flower pgirts in 3's; fi*uit indehiscent, 3-angled (fig. 7); emersed 



leaves foliaceous, several cm long (fig. 7). 



^ 2. Proserpinaca 



Myriophyllum (Water Milfoil) 



Submersed or amphibious perennials (overwintering chiefly by 

 turions); leaves cauline, whorled or alternate, usually finely dissected; 

 flowers sessile, single in axils of leaves or bracts; fruit a schizocarp, 

 splitting into 1-seeded nutlets. 



Key to Species 



Leaves scale-like, roundish (fig. 2D) or absent. 



1. M. tenellum 



Leaves pinnately divided, segments filiform (figs. 3-6). 

 2. Flowers and fruits in axils of submersed leaves (fig. 3). 



3. Fruits smooth, rounded on back or minutely papillate (fig. 

 3B,D), 0.7-1.2 mm long; plants submerged or amphibious; win- 

 ter buds (turions) absent. 

 2. M. humile 



3. Fruits rough with prominent dorsal tuberculate ridges (fig. 3F), 

 2.0-2.5 mm long; plants always submerged; winter buds (tur- 

 ions) formed in fall. 



3. M farwellii 



2. Flowers and fruits in axils of emersed bracteate leaves, forming 

 an erect spike (figs. 4C,5A,5G). 



4. Uppermost flowers alternate; leaves alternate or whorled. 



5. Submersed leaves whorled; bracts entire or serrate, no more 

 than twice the length of the flowers. 

 4. Af. alterniflorum 



5. Submersed leaves alternate; bracts pinnately divided, usu- 

 ally more than twice the length of the flowers. 



5. M pinnatum 



4. Uppermost flowers opposite; leaves whorled, or pseudo- 

 whorled. 



6. Bracts usually more than twice as long as pistillate flowers. 



