NAIADACEAE 39 



13. Potamogeton diversifolius Raf. Stems elongated, flattened or nearly terete, 

 branched : leaves various ; blades of 2 kinds ; those of submerged leaves linear-setaceous, 

 2-8 cm. long, acute, 1-nerved ; those of the floating leaves leathery, elliptic or oval, some- 

 times oblong-lanceolate, 1-2.5 cm. long, obtuse or acute : petioles shorter than the blades 

 or rarely longer : peduncles various, emersed club-shaped, 6-14 mm. long ; submerged, 4-6 

 mm. long : spikes dense, 4-8 mm. long : drupelets cochleate, about 1 mm. long, 3-keeled ; 

 middle keel crest-like, 7-8-toothed ; lateral keels acute or obtuse. 



In pools and still water, Maine to Montana, Florida and Texas. Spring and summer. 



14. Potamogeton pectinatus L. Stems slender, 3-10 dm. long, or longer, repeat- 

 edly forking : leaves all submerged ; blades setaceous or filiform, 2-15 cm. long, 1-nerved 

 or nerveless : peduncles filiform, 5-30 cm. long : spikes interrupted, sometimes elongated ; 

 flowers in approximate whorls or these remote : drupelets cochleate, barely fleshy, 1.5 mm. 

 long, 3-keeled on the back, crestless, but with 4-5 teeth. 



In still or running fresh or salt water, Cape Breton Island to British Columbia, Florida, Texas and 

 California. Summer and fall. 



FAMILY 2. ZOSTERACEAE Dumort. EEL-GRASS FAMILY. 



Perennial marine herbs, with creeping rootstocks and flattened branching 

 stems. Leaves alternate, 2-ranked : blades several-nerved, linear from a 

 sheathing inflated base. Flowers monoecious, both kinds arranged alternately 

 on a flattened spadix ; this enclosed in a spathe. Perianth wanting. Stami- 

 nate flower a sessile 1-celled anther attached to the spadix. Pollen thread-like. 

 Pistillate flower a single pistil with an elongated style and 2 thread-like stigmas, 

 attached by its back to the spadix. Fruit a flask-shaped beaked utricle ; this 

 irregularly rupturing. Seeds ribbed : embryo ellipsoidal. 



1. ZOSTERA L. 



Characters of the family. EEL-GRASS. GRASS-WRACK. 



Leaves 0.5-1.5 dru. long, 1-nerved : seeds 1.5 mm. long. 1. Z. minor. 



Leaves 2-18 dm. long, 3-7-nerved : seeds 3 mm. long. 2. Z. marina. 



1. Zostera minor (Caval.) Nolte. Stems more or less elongated, often sparingly 

 branched. Leaves few ; blades narrowly linear, 0.5-1.5 dm. long, obtuse, 1-nerved, usually 

 about 1-5 mm. broad : spathe 1-1.5 cm. long : fruits flask-shaped, with an oval or broadly 

 oblong body in all about 3 mm. long, 4-5 maturing in a spathe : seeds nearly 1.5mm. long, 

 smooth or very faintly striate. 



In shallow water, Key West, Florida. Also in Europe. 



2. Zostera marina L. Stems slender. Leaf-blades linear, ribbon-like, 2-18 dm. 

 long, obtuse, 3-7-nerved : spadix 2.5-6.5 cm. long : flowers commonly 10-20 on each 

 spadix : fruits oblong, fully 3 mm. long, obtuse : seeds nearly cylindric, about 3 mm. long, 

 20-ribbed, truncate. 



In streams or ditches, on or near the coast, Greenland and Labrador to Florida, also from Alaska 

 to California, and on the coasts of Europe. Summer. 



FAMILY 3. NAIADACEAE Lindl. NAIAS FAMILY. 



Submerged herbs, with fibrous roots and slender branching stems. Leaves 

 alternate, opposite or whorled : blades various, dilated and sheathing at the 

 base, mostly toothed. Flowers dioecious, solitary in the axils. Staminate flow- 

 ers with a double perianth, the outer entire or 4-horned, the inner hyaline, ad- 

 hering to the solitary stamen. Anther sessile or short-stalked, 1-4-celled, apic- 

 ulate or 2-lobed at the apex. Pistillate flowers with a single ovary, topped by a 

 short style and 2-4 stigmas. Fruit a sessile drupelet, with acrustaceous pericarp 

 and a membranous epicarp. Seed solitary, filling the pericarp. Embryo con- 

 formed to the interior of the seed. 



1. NAIAS L. 



Characters of the family. 



Sheaths oblique, with margins minutely 10-20- toothed. 

 Leaf-margins with shallow inconspicuous teeth. 



Pericarp of the drupelets dull., with 16-20 rows of strong reticulations : leaf- 

 blades with 80-100 marginal teeth. 1. N. Guadalupensis. 

 with 30-50 rows of delicate reticulations : 

 teeth. 2. N. flexilis. 



Pericarp of the drupelets shining, w: 

 leaf-blades with 50-60 marginal 



