62 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



10. TYPHACEAE. Cat-tail Family. 



1. TYPHA L. Cat-tail. 



Staminate and pistillate portions of the spike distant; leaves 5 ram. wide. 



1. T. angustifolia, 

 Staminate and pistillate portions of the spike contiguous; leaves 10 mm, wide. 



2. T. latifolia. 



1. Typha angustifolia L. 



Marshes and wet places, forming; colonies. Eur., Asia, and N. Amer. north of Mex. 



2. Typha latifolia L. 



Marshes and wet places, forming colonies. Eur., Asia, and N. Amer. 



11. SPARGANTACEAE. Bur-reed Family. 



1. SPARGANIUM L. Bur-reed. 



Fertile flowers sessile; fruit broadly obovoid 1. S. eurycarpum. 



Fertile flowers short-pediceled; fruit fusiform. 



Inflorescence simple 2. S. americanum. 



Inflorescence with 1 or 2 weak branches from lower axils. 



2a. S. americanum androcladum. 



1. Sparganium eurycarpum Engelm. 



Frequent in swamps and marshy margins of streams. Fr. July-Aug. Widely dis- 

 tributed in N. Amer. 



2. Sparganium americanum Nutt. 



Frequent in the same situations as the last, but usually in shallower water. June- 

 July; fr. Sept. Eastern N. Amer. and Asia. 

 2a. Sparganium americanum androcladum (Engelm.) Fern. & Eames. 



Habitat and range same as for the species. (S. androcladum jMorong; S. simplex 

 androcladum Engelm.) 



12. POTAMOGETONACEAE. Pondweed Family. 



Leaves alternate; fruit subglobose, short-beaked; flowers perfect. 



1. POTAMOGETON. 

 Leaves opposite; fruit oblong, long-beaked; flowers monoecious. 



2. ZANNICHELLIA. 

 1. POTAMOGETON L. Pondweed. 



Leaves of two sorts, the thicker floating ones with a dilated petioled blade, different 

 in form from the thinner submersed ones. 



Submersed leaves less than 2 mm. wide 10. P. diversifoiius . 



Submersed leaves more than 2 mm. wide. 



Submersed leaves linear, with a broad, coarsely cellular-reticulate space each 



side of the midrib 1. p. epihydrus. 



Submersed leaves broader than linear, not differentially reticulate. 

 Floating leaves 30-50- veined ; submersed leaves large, wide, often much 



recurved 3. p. amplifolius . 



Floating leaves fewer-veined; submersed leaves narrowly lanceolate. 



2. P. americanus. 



