4 ZANNICHELLIACEAE. 



Pollen-grains simple : pistillate part of the rachis with persistent pedicels 1 mm. long 

 or less. 1. T. angustifolia. 



Pollen-grains in 4's : pistillate part of the rachis with persistent 



pedicels 2-3 mm. long. 2. T. latifolia. 



1. T. angustifolia L. Stem slender, 1.5-3 m. tall: leaf -blades 5-15 mm. wide: 

 spike brown, the pistillate portion 0.5-1.5 cm. thick, separated from the 

 staminate : stigmas narrow : nutlets terete. Eare, in shallow water or mud. 



2. T. latifolia L. Stem stout, 1-2.5 m. tall: leaf -blades 10-25 mm. wide: spike 

 dark-brown or black, the pistillate portion 2.5-3 cm. thick, contiguous to the 

 staminate : stigmas spatulate or rhomboidal : nutlets furrowed. Common, in 

 ponds and still water. 



FAMILY 2. SPARGANIACEAE. BUR-REED FAMILY. 



Spikes in racemes or panicles, or spicate, their bracts persistent. 

 Perianth of scales. Pistil sessile : stigma subulate, sometimes oblique. 



1. SPARGANITJM [Tourn.] L. Plants growing in low grounds or deep 

 water. Leaves erect and triangular-keeled at the base or floating and flat. 

 Sum. BUR-REED. 



Achenes fusiform, the body stalked. 



Inflorescence branched, the branches geniculate and bearing 3 or more staminate 

 spikes. 1. S. androcladum. 



Inflorescence simple, or if branched the branches strict and 



bearing less than 3 staminate spikes. 2. S. americanum. 



Achenes obovoid or obpyramidal, sessile. 3. S. eurycarpum. 



1. S. androcladum (Engelm.) Morong. Plants 2-7 dm. tall, branched: stami- 

 nate heads mostly less than 1 cm. thick: fruit-heads 1-2 cm. thick: achene-body 

 6-7 mm. long, abruptly narrowed at the apex, long-stipitate. N.S. Common, 

 in shallow water. Sandstones and shales, schists. 



2. S. americanum Nutt. Plants 2-8' dm. tall, simple, the lower flower-heads 

 sometimes peduncled: achene-body about 5 mm. long, short-stipitate, gradually 

 narrowed at the apex. M. Kare, in shallow water. Limestones. 



3. S. eurycarpum Engelm. Plants 8-20 dm. tall: staminate heads about 1 cm. 

 thick: fruit-heads 2.5-3 cm. thick: achene-body 7-8 mm. long, rounded or 

 depressed at the apex, sessile. Susquehanna valley. Rather rare, in shallow 

 water. 



Order NAIADALES. 



Perennial, aquatic or marsh herbs. Leaves various, sometimes mere 



phyllodia. Flowers usually symmetrical. Perianth wanting or imperfect. 



Androecium usually of 1-4 stamens. Gynoecium simple or several- 

 carpellary. 



Gynoecium of distinct carpels : anthers with petal-like connectives : leaf-blades not 

 spiny-toothed. Fam. 1. ZANNICHELLIACEAE. 



Gynoecium of united carpels : anthers with inconspic- 

 uous connectives : leaf -blades spiny-toothed. Fam. 2. NAIADACEAE. 



FAMILY 1. ZANNICHELLIACEAE, PONDWEED FAMILY. 



Aquatic caulescent herbs. Leaves alternate, filiform, _or with blades, 

 entire. Flowers perfect or monoecious, in spikes or clusters from a spathe. 

 Androecium of 1, or mostly 2-4, distinct stamens. Gynoecium of several 

 distinct carpels. Fruit a cluster or spike of drupelets. 



1. POTAMOGETON [Tourn.] L. Herbs growing mostly in fresh water. 

 Leaves various, the submerged and the floating ones usually different. Flowers 



