NAIADACEAE. 21 



2. Typha angustifolia L. 'M. p. 39. lu marshes. Summer, 



Family 2. SPARGANIACEAE Agardli. Bur-reed Family. 



1. SPARGANIUM L. Bur-Eeed. 



Fruit sessile. 1. S. eurycarpum. 



Fruit stalked. 2. S. androcladim. 



1. Sparganium eurycarpum Engelm. M. p. 39. Marshes and along streams. 



Summer, 



2, Sparganium androcladum (Engelm.) Morong, M, p, 39, Bogs or shal- 



low water. Summer, 



Order 2, NAIADALES. 



Perianth, if present, inferior; carpels mostly distinct. 

 Perianth-segments, when present, herbaceous. 



Carpels distinct ; aquatic herbs. Fam. 1. Naiadaceae. 



Carpels united until maturity; bog plants; flowers racemed or 

 spiked. Fam. 2. Scheuchseriaceae. 



Perianth of two series of segments, the outer green; the inner mostly 

 white. Fam. 3. Alismaceae. 



Perianth superior; carpels united, Fam. 4. Vallisneriaceae. 



Family 1. NAIADACEAE Lindl. 



Flowers perfect. 



Perianth of 4 distinct segments. 1. Potamogeton. 



Perianth none; flowers naked. 2. Buppia. 



Flowers monoecious or dia3cious. 

 Leaves entire. 



Leaves 1-nerved, 2-8 cm, long, 0,5 mm, or less wide, 



3, Zannicliellia. 

 Leaves many-nerved, 0.3-1.6 m. long, 2-8 mm. wide. 



5. Zostera. 

 Leaves spiny-toothed on the margins. 4. Naias. 



1, POTAMOGETON L, Pondweed, 



Stipules axillary and free from the leaf. 

 "With floating and submerged leaves. 

 Submerged leaves bladeless. 



Drupelets barely keeled; nutlets more or less pitted, 



1. P. natans. 

 Drupelets 3-keeled; nutlets not pitted, 2, P, Oalesianus. 



Submerged leaves with a proper blade. 



Submerged leaves of 2 kinds, lanceolate and oval or oblong. 

 Uppermost leaves broadly oval or elliptic, lowest lanceo- 

 late, 3. P. amplifolius. 

 Uppermost leaves lanceolate and pellucid, lowest oblong 

 and opaque. 4. P. pulcher. 

 Submerged leaves all alike. 



Blades of the submerged leaves linear or nearly so 

 throughout. 

 Blades the same breadth throughout, obtusely pointed, 

 coarsely cellular-reticulated in the middle. 



5. P. Nuttallii. 

 Blades dilated at base, acute, without cellular reticu- 

 lation. 7. P. heterophyllus. 



Blades of the submerged leaves lanceolate. 



6. P. lonchites. 



