36 ZANNICHELLIACEAE 



sessile or peduncled, accrescent : bractlets broadened upward, as many as the angles of the 

 nutlets, entire or eroded at the apex : fruiting heads globose, 2-2.5 cm. in diameter : nutlets 

 6-10 mm. long, sessile, 4-5-angled, rounded or depressed at the apex, tipped with the style. 

 Along streams or in marshes, Newfoundland to British Columbia, North Carolina and California. 



Order 2. NAIADALES. 



Aquatic or marsh-inhabiting herbs, perennial by rootstocks. Leaves various, 

 sometimes reduced to phyllodes, sometimes with both narrow and broad blades 

 on the same plant. Flowers perfect, monoecious or dioecious, usually with an 

 unequal number of parts in the whorls. Perianth wanting or very imperfect. 

 Androecium of 1-4 stamens or sometimes more. Gynoecium of 1 or several 

 distinct or united carpels. Endosperm scant or wanting. 



Gynoecium of distinct carpels : stigmas disk-like or cup-like. Fam. 1. ZANNICHELLIACEAE. 



Gynoecium of united carpels: stigmas 2-4, slender. 



Staminate and pistillate flowers alternating on a slender spadix, later- 

 ally attached : leaves with entire blades. Fam. 2. ZOSTERACEAE. 

 Staminate and pistillate flowers axillary, attached at the base : leaves 



with spiny-toothed blades. Fam. 3. NAIADACEAE. 



FAMILY 1. ZANNICHELLIACEAE Dumort. PONDWEED FAMILY. 



Perennial submersed caulescent herbs. Leaves alternate, sometimes clus- 

 tered : blades filiform or expanded. Flowers perfect or monoecious, in axillary 

 sometimes peduncled spikes or clusters arising from a spathe. Perianth a hya- 

 line envelope, or wanting. Androecium of 1-4 stamens or rarely more. Fila- 

 ments distinct, hypogynous in the perfect flowers. Anthers 1-2-celled, extrorse. 

 Gynoecium of several distinct carpels. Ovaries 1-celled. Ovule solitary. Fruit 

 a spike or cluster of drupelets. Endosperm wanting. 



Stamens 2 or sometimes solitary, the connectives without appendages : drupelets manifestly stipitate. 



Stigma terminating a long style : anther 1. 1. ZANNICHELLIA. 



Stigma sessile : anthers 2. 2. RUPPIA. 



Stamens 4, the connectives with dilated appendages : drupelets sessile. 3. POTAMOGETON. 



1. ZANNICHELLIA L. 



Delicate submerged herbs, with filiform branching flaccid stems. Leaves alternate : 

 blades slender, entire, 1-nerved, tapering from the dilated base. Flowers monoecious, both 

 kinds in the same axils ; staminate of a single stamen : anther 2-4-celled, terminating a 

 pedicel-like filament. Pistillate flowers consisting of a gynoecium of 2-6 sessile carpels. 

 Ovary flask-shaped : stigma peltate or somewhat cup-shaped, with uneven edges, surmount- 

 ing a long style. Fruit a cluster of somewhat elongated curved stalked drupelets, these 

 ribbed, sometimes toothed on the back. Seed with a coiled embryo. 



1. Zannichellia paliistris L. Stems filiform, 2-7 dm. long, sparingly branched : 

 leaves numerous ; blades soft, narrowly linear, 2-9 cm. long, acute, 1-nerved : stipules or 

 spathes persistent, separating from the leaves : peduncles very short : pedicels obsolete 

 or wanting : drupelets 2-4, or sometimes 6 in a cluster, oblong or oblong-falcate, 2-4 mm. 

 long, tipped with the persistent style, maturing under water. 



In fresh or brackish ponds or ditches, throughout North America, except the extreme north. 

 Summer and fall. Also throughout the Old World. 



2. RUPPIA L. 



Submersed delicate herbs, with filiform branching stems and elongated rootstocks. 

 Leaves alternate : blades 1-nerved, tapering to a hair-like apex from a more or less dilated 

 basal sheath. Flowers perfect, terminating spadix-like peduncles. Perianth wanting. 

 Stamens 2 : anthers sessile ; sacs large, separate, attached by their backs to the rachis. 

 Pistils 4, sessile : stigmas sessile, peltate. Fruit a cluster of several oblique stipitate drupe- 

 lets. Embryo with the hypocotyl and the inflexed cotyledonary end immersed. 



1. Ruppia maritima L. Foliage deep green. Stems slender, 3-10 dm. long, often 

 whitish ; internodes unequal in length : leaf-blades narrowly linear, or filiform, 2.5-4 cm. 



