LEMNACEAE. 71 



large, sharp pointed; spathe a complete sac, opening at the upper 

 end; pistil flask-shaped; fruit somewhat winged; seed slightly com- 

 pressed, smooth. 



Near San Bernardino, Parish. This, as* well as all the other 

 members of the family occurring with us, is rarely fertile. 



2. LEMNA L. Duckweed. 



Stipe attached to the basal margin of the frond. Re- 

 productive pouches 2, triangular, opening as clefts in 

 either margin of the basal portion of the frond. Root 

 solitary. Spadix of 1 pistillate and 2 staminate flowers; 

 spathe various; filaments curving upward from the 

 margin of the frond. Anthers 2-celled, transversely 

 dehiscent. 



Fronds with a short stipe; floating on the surface. 

 Spathe sac-like. 



Frond pale beneath, usually strongly gib- 



bose. 1. L. gihha. 



Frond green or purplish beneath. 2. L. minor. 



Spathe open. 



Frond thin, without papules. 3. L. cyclostasa. 



Frond thick, with a row of papules along 



the nerve. 4. L. mhiima. 



Fronds long-stipitate, mostly submerged. 5. L. trisulca. 



1. L. gibba L. Fronds from solitary to 4 in a colony, commonly 2, 

 orbicular to obovate, 2-5 mm. long, 2-4 mm. wide, more or less 

 unsymmetrical, thick, convex and slightly keeled above, usually 

 more or less gibbous beneath, usually 3-5-nerved; fruit winged with 

 rounded lobes on either side of the stigma; seeds 1-7. 



Common in slow-running streams and ponds. 



2. L. minor L. Fronds solitary or w4th 2 or more in a colony, 

 round to elliptic-obovate, 2-4 mm. long, 1.5-3 mm. wide, sym- 

 metrical, thickish, convex on both sides, upper surface sometimes 

 keeled and with a row of papulae along the midnerve, obscurely 

 3-nerved; fruit not winged; seeds solitary. 



Apparently less common than the last. 



3. L. cyclostasa (Ell.) Chev. Fronds commonly in colonies of 

 2-8, oblong to obovate-oblong, usually somewhat falcate, 2.3-4.5 

 mm. long, 0.7-1.5 mm. wide, usually strongly unsymmetrical; fruit 

 elongated-ovate, slightly unsymmetrical; seed oblong-ovoid. (L. 

 valdiviana Phil.) 



Common throughout our range. 



4. L. minima Phil. Fronds commonly in colonies of 2, oblong 

 to elHptic, 1.5-3.9 mm, long, 0,9-2.7 mm. wide, slightly to promi- 

 nently convex above, with a row of papulae along the midnerve, 

 convex below, commonly nerveless; pistil short, clavate; seed oblong, 

 pointed. 



Near San Bernardino, Parish; Bear Valley, San Bernardino 

 Mountains; Lakeside, San Diego County. 



