129. POTAMOGETONACEAE 277 



6. Blades usually with a pair of small transluccnl glands 

 at the base. 

 7. Leaves gradually tapering to a bristle tip, revolute, 

 rigid; shallow water, Wolf Lake, Cook Co., A. 



Chase P. strictifolius Bcnn. 



7. Leaves not bristle-tipped. 



8. Peduncles filiform, 3-8 mm long; stipules partly 



connate; lakes, etc. [P. panormitaniis Riv.] 



P. pusillus L. 



8. Peduncle 0.5-3 cm long; stipules not connate; 

 ditches, rare; Lake Co P. berchtoldi Fieber 



3. Stipules adnate to the base of the leaves. 



9. Leaves filifonn, less than 0.6 mm wide, entire; lakes and 

 ponds, locally abundant P. pectinatus L. 



9. Leaves linear, 2-ranked, 3-6 mm wide, the margin micro- 

 scopically serrulate; lakes, rare; Lake Co 



P. rnhhinsii Oakes 



2. Leaves lanceolate to elliptical or ovate. 

 10. Leaves clasping the stem. 



IL Leaves slightly clasping at base, cucullate at the apex, 

 mostly 8-30 cm long; fruits 4-5 mm long; lakes in Cook. 



Lake, and McHenry counties P. praelongus Wulfen 



11. Leaves mostly 2-8 cm long, strongly clasping at the base, 

 the apex flat, not cucullate; fruits 2.5-4 mm long; lakes 



in Cook, Kankakee, Lake, and McHenry counties 



P. richardsonii (A.Benn.) Rydb. 



10. Leaves sessile, not clasping, linear-elliptical, 5-12 mm 

 wide, obtuse, undulate or crisped, 3-5-nerved; ponds and 

 streams, not common; introd. from eastern U.S.; nat. 

 from Eur. May-Sept P. crispus L. 



Leaves of two kinds, broader floating ones, and narrower sub- 

 merged ones. 

 12. Submerged leav-es lanceolate to elliptical, more than 5 mm 

 wide. 

 13. Stem usually black-spotted; principal floating leaves some- 

 what cordate at base; fruit 3-3.5 mm long; shallow 



water in Mason, Menard, and St. Clair counties 



P. pulcher Tuckerm. 



13. Stem not black-spotted; leaves tapering at the base, or 

 rounded. 

 14. Floating leaves with 30 or more principal veins; lakes 

 and ditches, local; Cook, l)u Page, Lake, and Wa- 

 bash counties P. amplifolius Tuckerm. 



14. Floating leaves with fewer veins. 

 15. Mature spikes 4-6 cm long. 



16. Floating leaves elliptical, not nuicronate, 4-9 cm 

 broad; submerged leaves lanceolate; style 

 prominent on the fruit; streams and ponds 



