366 
LEMNACEAE. 
1. Lemna trisalca I. Ivy-leaved Duckweed. Star Duckweed. 
(Fig. 885.) 
Lemna trisulca I,. Sp. Pl. 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, 1/’-114’’ 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 20-ribbed. 
In pools and rivers, southern New York and New Jersey and 
southward, west to California, Arizona and New Mexico. Also 
in South America. 
4. Lemna minor]. Lesser Duckweed. (Fig. 888.) 
Lemna minor I,. Sp. Pl. 970. 
Thallus obovate or subcircular, 1/’-3’’ long, thickish, rarely 
reddish or purplish tinged, short-stalked when young, pro- 
vided throughout with stomata, obscurely 3-nerved, very rarely 
4-5-nerved. Rootcap obtuse or subtruncate. Fruit symmetri- 
cal, subturbinate. Seed with a prominent protruding hilum, 
deeply and unequally 12-15-ribbed. 
In ponds, lakes and stagnant waters, throughout North America 
below 58° N. lat. Also in Europe, Asia, Africa and Australia. 
Summer, 
1753: 
3. Lemna perpusilla Torr. Minute Duckweed. 
(Fig. 887.) 
Lemna perpusilla Torr, Fl. N. Y. 2: 245. 1843. 
Thallus small, 1/’-114’’ 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-60-ribbed. 
In ponds, rivers, springs and lakes, New York and New Jersey to 
Minnesota, Nebraska and Missouri. June-July. 
