26 FAM. 14, 15, 16. 



or peduncled, finally twice as large as the staminate, together forming an interrupted 

 spike. In shallow water. Summer. 



14. Zannichelliaceae, Pondweed Family. 



Submerged herbs with alternate or clustered leaves 

 on slender stems; flowers perfect or monoecious in axil- 

 lary spikes arising from a bract-like spathe; perianth want- 

 ing. 



1. Leaves alternate, flowers perfect, stamens 2, pistils 4, - Ruppia, Ditch-grass 



R. maritima. Leaves almost filiform. In brackish water. Summer. 

 1. Floating leaves smaller and thicker than submerged leaves; flowers 



perfect, stamens 4, pistils 4, - - - Potamogeton, Pondweed 



P. Lonchitis (fluitans). Stems long, branched; submerged leaves large, lan- 

 ceolate, pellucid; floating ones oblong, half as long as the submerged; 

 stipules free from the leaves; peduncles short; spikes cylindric. In ponds 

 and rivers. Summer. 

 P. diversifolius (hybridus). Stems very slender, branched; submerged leaves 

 filiform, setaceous; floating ones elliptic, leathery; stipules adnate to 

 the submerged leaves; peduncles short; spikes oblong. Shallow ponds. 

 Summer. 



15. Alismaceae, Water-Plantain Family. 



Acaulescent marsh-herbs with sheathing leaves and 

 mostly simple scapes, bearing the terminal racemes or 

 panicles; calyx of 3 persistent sepals; corolla, white or 

 pink, of 3 decidous petals; stamens 6-many; ovaries 1- 

 celled, each cell 1-ovuled; fruit a head of achenes. 



1. Flowers perfect or polygamous; stamens 12-30; fruit a bristly head. 



Spring and Summer, --_-___ Echinodorus 



E. parvulus. Flowers in terminal umbelled clusters, leaves linear. Shallow 



ponds. 

 1. Flowers mcncecious or dioecious in whorls of 3 near the top of the 



scape, the upper whorls staminate; stamens many, pistils many; 



fruit a globular head. Summer and Fall. - - Sagittaria, Arrowheads 

 S. natans. Pedicels of fertile flowers thickened, reflexed at maturity; stam- 

 ens 7 or 8; scapes simple, leaves elliptic, floating. Ponds. 

 S. graminea (simplex). Pedicels of fertile flowers slender; stamens 10-12, hairy; 



scapes slender; leaves linear. Ponds. 

 S. lancifolia (falcata). Pedicels of fertile flowers slender and shorter than those 



of sterile flowers; scapes tall, often branched; leaves elliptic, leathery. 



Lakes and marshes. 

 S. pubescens (variabilis). Pedicels of fertile flowers slender and half as long 



as those of sterile flowers; scapes sometimes pubescent; leaves mostly 



sagittate and often pubescent; whorls of inflorescence remote. Marshes. 



16. Elodeacea, Tape-Grass Family. 

 Submerged herbs; perianth regular, 6 in two rows, 



