SPARGANIACEAE. 25 



Sparganium minimum Fries. Aquatic; stems very slender, 10-40 cm. long; 

 leaves thin and grass-like, 2-4 mm. broad, floating; inflorescence simple; 

 heads sessile or nearly so, the pistillate about 1 cm. in diameter when mature; 

 nutlets smooth, ovoid, conically short-beaked, easily detached. 



In mountain ponds and lakes. San Juan Lake, Vancouver Island, Rosen- 

 dahl & Brand; Mount Rainier, Piper. 



Sparganium angustifolium Michx. Aquatic; stems slender, 30-100 cm. 

 long; leaves very long and narrow, rather firm, 2-4 mm. wide; inflorescence 

 simple; heads sessile or the lower peduncled, the pistillate 15-20 mm. in di- 

 ameter when mature; nutlets abruptly slender-beaked, firmly attached. 



In ponds and lakes; Mount Arrowsmith, Vancouver Island, Macoun. 



Family 12. NAJADACEAE. PONDWEED FAMILY. 



Submersed or floating fresh-water or marine aquatic herbs 

 or marsh plants; leaves flat or filiform, opposite, alternate or 

 whorled; flowers unisexual or perfect, mostly small, solitary 

 axillary or in spikes; perianth none or sheath-like; stamens 

 1-4; carpels 1-5, each 1-ovuled. 



Flowers perfect; stamens more than one. 



Perianth of 4 sepals; stamens 4; fruit sessile. 35. POTAMOGETON, 25. 



Perianth none; stamens 2; fruits stalked. 36. RUPPIA, 27. 



Flowers monoecious or dioecious; stamen solitary. 

 Leaves many, opposite; flowers axillary, sessile. 

 Monoecious; pistils 2-5, in a cup-shaped invo- 

 lucre; stigmas short. 37. ZANNICHELLIA 27. 

 Dioecious; pistil solitary, naked; stigma slender. 38. NA]AS, 28. 

 Leaves alternate, rather few. 



Stigma capitate; fertile flowers in an exserted 



naked spike; fresh water or marsh plant. 39. LILAEA, 28. 

 Stigma linear; fertile flowers on an enclosed 



spadix; marine plants. 



Monoecious; fruit rounded at base. 40. ZOSTERA, 28. 



Dioecious; fruit cordate at base. 41. PHYLLOSPADIX, 28. 



35. POTAMOGETON. PONDWEED. 



Leaves alternate or the uppermost opposite, often of two 

 kinds, the submersed mostly linear, the floating lanceolate, 

 ovate or oval; spathes enclosing the young buds, usually perish- 

 ing soon after expanding; flowers small, perfect, spicate, green 

 or red; perianth of 4 sepals, valvate in bud; stamens 4, opposite 

 the sepals; ovaries 4, sessile, distinct, 1-celled, 1-ovuled. 



Leaves of two kinds, the floating ones thickish, the submersed 



thin and of different form. 

 Submersed leaves linear. 



Floating leaves subcordate at base; stipules long. P. natans. 

 Floating leaves acute at base; stipules short. P. epihydrus. 



Submersed leaves lanceolate or oval. 



Floating leaves oval, 30-50-nerved. P. amplifolius. 



Floating leaves narrowly elliptic, 10-20-nerved. 



