MACLOSKIE: POTAMOGETONACE^E. 147 



Family 6. POTAMOGETONACE.E. Pondweed. 



Submerged plants with kotty-jointed stems and alternate (rarely oppo- 

 site) leaves. Flowers small, i -sexual or hermaphrodite, regular, perianth 

 4-leaved or none or a cup. Anthers 4 or 2, sessile. Carpels i or more, 

 usually free ; each with i pendent seed. Achenes hard or leathery. Endo- 

 sperm none. 



Species 25, chiefly of temperate zones. 



KEY TO THE GENERA. 



1. Flowers naked, at length long-stalked. Leaves slender, acuminate. In brackish water. 



i. Ruppia. 



2. Sepals 4. Flowers spicate. Leaves of two kinds, the floating broader than the submerged. 



Chiefly in fresh water. 2. Potamogeton. 



i. RUPPIA Linn. 



Stems capillary, branching. Leaves slender, i -nerved, acuminate, with 

 thin sheaths. Flowers monoecious, in a spathe, at length long-peduncled, 

 having two sessile anthers and two sets of pistillate flowers on opposite 

 sides of the rachis ; without perianth (or a single hermaphrodite flower 

 having 2 stamens and 4 carpels). The male flowers fall off and after fer- 

 tilization the peduncles twist, drawing the ripening fruit below the water. 



R. MARITIMA Linn. 



Leaves 2-7 cm. long, .5 mm. wide. Drupes stipitate, 2 mm. long. 

 (Cosmopolitan, in brackish water) ; S. Patagon. (Dusen). 



2. POTAMOGETON Linn. Pondweed. 



Leaves flat, often of two kinds, submerged and floating; the floating 

 being firmer and broader. Spathes, or stipules, at base of the leaves or 

 the petioles, and usually perishing soon after expanding. Peduncles 

 axillary, usually emersed, bearing a spike of small flowers. Perianth- 

 leaves, stamens and carpels each 4. Seeds curved. 



Species 65, in temperate regions. 



KEY TO THE SPECIES. 

 a. Leaves floating and submerged. 

 b. Stipules free. Fruit pitted. 



c. Submerged leaves reduced to petioles. natans. 



c2. Submerged leaves with lamina. fluitans. 



