276 American Midland Naturalist Mop^ograph No. 7 



Lake, McHenry, and Peoria counties. June-July 



- T. maritima L. 



1. Carpels 3, in fiaiit clavate, 7-8 mm long; calcareous soil, rare; 

 Cook, Kane, Kankakee, Lake, McHenry, Peoria, and Tazewell 

 coimties. July-Sept 7\ polustris L. 



2. Scheuchzeria L. 



S. americana (Fern.) G.N.Jones. Bogs, rare; Fulton, Lake, 

 McHeniy, and Menard counties. June-July. [S. palustris sensu Am. 

 auth., non L. ; S. palustris var. americana Fern.]. On the basis of shape 

 and size of follicles, our plants appear specifically distinct from the 

 European S. palustris L. 



128. Naiadaceae Lindl. — Naiad Family 

 1. Naias L. — Naiad 



1. Fruit glossy, with 30-50 longitudinal lines; style 1-2 mm long; 

 leaves with 20-30 minute teeth on each margin ; ponds and slow 

 streams throughout 111. June-Aug A'', fle.xilis (Willd.) R. & S. 



1. Fruit dull, with 10-20 rows of distinct reticulations; style 0.2- 

 0.6 mm long; leaves with 40-50 minute teeth on each margin; 

 ponds and shallow lakes, rare; Lake, Macoupin, Peoria, and 



Williamson counties. July-Sept 



- -- N. guadalupensis (Spreng.) Magnus 



129. Potamogetonaceae Engler — Pondweed Family 

 [Zosteraceae Dumort.) 

 1. Flowers perfect, in spikes; leaves alternate, or the upper sometimes opposite 



1. Potamogeton 



1. Flowers unisexual, axillary; leaves opposite, filiform, 1 -veined, entire 



2. Zannichellia 



1. Potamogeton L. — Pondweed 



1. Leaves uniform, all submerged. 

 2. Leaves linear to filiform. 



3. Stipules free from the petioles and blades. 



4. Leaves 9- to 35-veined; fruits 3.5-5 mm long; lakes, chief- 

 ly in Cook, Kankakee, Lake, McHenry, Menard, 

 and Winnebago counties. [P. compressus Am. auth., 



non L.] P. zosteriformis Fern. 



4. Leaves 1- to 7-veined; fruits 1.5-3 mm long. 



5. Leaves 5- to 7-veined, with a pair of basal glands; 

 stagnant water, rare; Cook, Jackson, and Lake 



counties. [P. rnucronatus Schrad.] P. friesii Rupr. 



5. Leaves 1- to 3-veined. 



6. Blades usually without basal glands; fruiting spikes 

 subcapitate, 2-8 mm long; ponds, ditches, and 



streams, chiefly in the northern half of 111 



P. foliosus Raf. 



