366 



LEMXACEAE. 



i. Lemna trisulca L. 



Ivy-leaved Duckweed. Star Duckweed. 

 (Fig. 885.) 



Lemna trisulca L. Sp. PI. 970. 1753. 



Thallus lanceolate, submerged and devoid of stomata in 

 the primary aquatic form, ovate to oblong-lanceolate, 6 "-9" 

 long, floating and provided with stomata in the later flower- 

 ing stage. The later and more common form is narrowed at 

 the base to a slender stipe, thin, denticulate, with or without 

 rootlets, and slightly 3-nerved. Several individuals often 

 remain connected, so as to form a chain-like series. Root- 

 cap pointed; fruit symmetrical; seed deeply 12-15-ribbed. 



In ditches, springs, ponds, shallow lakes and sloughs. Nova 

 Scotia to the Pacific Ocean, south to New Jersey and New Mex 

 ico. Also in Europe. Asia, Africa and Australia. July-August. 





2. Lemna Valdiviana Philippi. Valdivia Duck- 

 weed. (Fig. 886.) 



Lemna Valdiviana Philippi, Linnaea, 33: 239. 1864. 



Thallus oblong-elliptical, i // -i^ // long, thin, subfalcate 

 and shortly stalked at the base, provided with numerous 

 stomata, except on the borders, nerveless; rootcap short and 

 blunt; spathe reniform; fruit ovoid-oblong, unsymmetrical; 

 seed prominently ao-ribbed. 



In pools and rivers, southern New York and New Jerse3' and 

 southward, west to California. Arizona and New Mexico. Also 

 in South America. June-July. 



3. Lemna perpusilla Torr. Minute Duckweed. 

 (Fig. 887.) 



Lemna perpusilla Torr. Fl. N. Y. 2: 245. 1843. 



Thallus small, \"-\y 2 " long, obovate, often purplish tinged 

 beneath, unsymmetrical and abruptly narrowed to a very short 

 stalk, provided throughout with numerous stomata, more or 

 less 3-nerved; rootcap pointed; fruit ovoid; seed 4o-6o-ribbed. 



In ponds, rivers, springs and lakes, New York and New Jersey to 

 Minnesota, Nebraska and Missouri. June-July. 



4. Lemna minor L. Lesser Duckweed. (Fig. 888.) 



I^emna minor L,. Sp. PI. 970. 1753. 



Thallus obovate or subcircular, i // -3 // long, thickish, rarely 

 reddish or purplish tinged, short-stalked when young, pro- 

 vided throughout with stomata, obscurely 3-nerved, very rarelv 

 4~5-nervcd. Rootcap obtuse or subtruncate. Fruit symmetri- 

 cal, subturbinate. Seed with a prominent protruding hilutn, 

 deeply and unequally i2-is-ribbed. 



In ponds, lakes and stagnant waters, throughout North America 

 below 58 N. lat. Also in Europe, Asia, Africa and Australia. 

 Summer. 



