360 LEMNACE.E. (DUCKWEED FAMILY.) 



Var. androcladum, Engelm. Stouter and taller : inflorescence branched 

 below ; branches bearing numerous sterile heads : fruit larger, not contracted, 

 long-tapering at both ends. Gray's Manual, 481. 



Var. angustifolium, Engelm. Leaves floating : inflorescence simple : 

 fruit smaller, short-stiped, contracted in the middle. Loc. cit. 



# # # Usually floating, with very slender stems and delicate always flat and 

 narrow leaves : inflorescence simple, of few small heads : scales oval or obovate, 

 denticulate : nuts oval, with a very short stipe and short point. 

 3. S. minimum, Bauhin, Fries. Fertile heads solitary or two, axillary, 

 sessile, or the lower one peduncled : nuts somewhat triangular, contracted 

 below : stems when out of the water only 5 to 6 inches high. Uinta Moun- 

 tains, and northward, thence eastward to New England. 



ORDER 84. L,EUINACEjE. (DUCKWEED FAMILY.) 



Minute stemless plants, floating free on the water, destitute of distiuct 

 stem and foliage, being merely a disk-like frond producing one or few 

 monoecious flowers from the edge or upper surface, and commonly hang- 

 ing roots from underneath ; fruit a utricle, and seed large. 



1. Liemna. Frond 1 to 5-nerved, with a single rootlet. 



2. Speirodela. Frond 7 to 11-nerved, with several rootlets. 



1. LEMNA, Linn. DUCKWEED. DUCK'S-MEAT. 



Flowers marginal, bracteate, diandrous. Anther-cells bilocellate by a trans- 

 verse partition, dehiscing transversely. Seeds 1 to 6. Rootlet destitute of 

 vascular tissue. 



1. L. trisulca, L. Fronds thin, oblong or oblong-lanceolate, attenuate at base 

 into a slender stalk, very obscurely 3-nerved, usually several series of offshoots 

 remaining connected: seeds ovate. From New Mexico to Oregon, the Sas- 

 katchewan, and eastward through most of North America. 



2. Ii. minor, L. Fronds rather thick, round- to elliptic-obovate, sessile, very 

 obscurely 3-nerved, the offshoots soon separating : seeds oblong-obovate. 

 Abundant everywhere, closely covering the surface of stagnant pools. 



2. SPEIRODELA, Schleiden. 



Like Lemna, but anther-cells bilocellate by a vertical partition and dehiscent 

 longitudinally, and ovary 2-celled. Rootlets with axile vascular tissues. 



1 . S. polyrrhiza, Schleid. Fronds round-obovate, purple beneath : roots 

 clustered, usually 3 to 5. Lemna polyrrhiza, L. Nevada, Montana, Wyoming, 

 and eastward throughout the continent. Very rarely seen in flower or fruit. 



