Fig. 292: Lemna minima: a, habit, showing flowering fronds with long, solitary 

 roots, X 2; b. habit, top view of fronds with flowers and fruits, X 4; c, frond (longi- 

 tudinal section), the air spaces in a single layer, X 12; d and e, root tips, with and with- 

 out rootcap, X 20; f and g. pistillate and staminate flowers, the broad enclosing spathe 

 reniform and open on one side, X 48; h and i. fruits, slightly flattened, X 16; j and k. 

 mature seeds, longitudinally ribbed and cross-striate, X 16. (From Mason, Fig. 162). 



2. Lemna valdiviana Phil. Fig. 291. 



Thallus narrowly elliptic to oblong or oval, solitary or several together, 2-5 

 mm. long, 0.5-2 mm. wide, symmetrical to somewhat falcate, obscurely 1 -nerved 

 or nerveless, the dorsal surface of conspicuously imiform texture throughout, 

 light green and often translucent. 



In ponds, lakes, ditches and about springs in s.e. Okla. (McCurtain Co.), 

 throughout Tex. and Ariz. (Coconino, Greenlee, Pima and Yavapai cos.); wide- 

 spread in the W. Hemis. 



3. Lemna minima Phil. Fig. 292. 



Thallus solitary or in small clusters, oblong to elliptic or somewhat ovoid, 

 1-2.5 mm. long, 0.7-1.5 mm. wide, sometimes with only occasional members 

 larger, thick, the dorsal surface convex, commonly nerveless or with an obscure 

 nerve and a row of papules along the middle, usually with a thin margin around 



570 



