Jones: Flora of Illinois, 25. Lemnaceae 87 



3. Peltandra Raf. 



P. virginica (L.) Kunth. Muddy margins of ditches or ponds, or in shal- 

 low water, or swamps, local; extending northw. to Kankakee and Peoria coun- 

 ties. May-June. 



4. AcoRUS L. — Sweetflag 

 A. calamus L. Swamps, or wet ground along streams, local. June-Aug. 



25. Lemnaceae Dumort. — Duckweed Family 



1 . Plants with roots. 



2. Root solitary, without vascular tissue 1. Lemna 



2. Roots several, each with a vascular bundle 2. Spnodela 



1. Plants without roots, ellipsoid, minute 3. Wolffia 



1. Lemna L. — Duckweed 

 L Plants paddle-shaped, 6-10 mm. long, remaining connected, wholly sub- 

 merged; ponds and ditches, local L. trisulca L. 



L Plants oval or roundish, 2-5 mm. long, soon separating, floating. 

 2. Plant-body symmetrical or nearly so. 



3. Plant round to oval, indistinctly 3-veined, dark green, biconvex; utricle 

 lenticular; stagnant water and slow streams, local L. minor L. 



3. Plant elliptical, indistinctly 1 -veined, pale green, nearly flat; utricle 



elongate; stagnant water, rare L. minima Phil. 



2. Plant-body asymmetrical. 



4. Plant obliquely obovate, 3-veined, thick, papillose on the median line; 



ponds and streams, local L. perpusilla Torr. 



4. Plant elliptical, often somewhat falcate, obscurely 1 -veined, smooth; 



ponds and swamps, rare. [L. cyclostasa of auth.} 



L. valdiviana Phil. 



2. Spirodela Schleid. 

 S. polyrhiza (L.) Schleid. Plants roundish-obovate, 3-8 mm. long, floating. 

 Ponds, ditches, slow streams, locally abundant. 



3. Wolffia Horkel 



{Brwuera Franch) 

 1. Plants globose or ellipsoid, not flattened, 0.5-1 mm. long, loosely cellular, 

 not punctate, floating somewhat beneath the surface; locally abundant in 



stagnant water W. columbiana Karst. 



1 . Plants flattened on the upper surface, brown-punctate, compactly cellular, 

 floating at the surface of the water. 

 2. Plants 1-1.5 mm. long, rounded-ovate, strongly gibbous, the upper surface 

 with a central conical papilla; in permanent pools of stagnant water, rare. 



Wabash Co., Schneck. W. papulifera Thompson 



2. Plants 0.5-0.8 mm. long, ellipsoid, slight gibbous, symmetrical, the upper 

 surface flat or slightly convex, gradually rising to the acute apex; stag- 

 nant water, rare; Sangamon Co., E. Hall W. punctata Griseb. 



