850 GUNNERACEAE 



upper. Flowers perfect, minute, axillary, greenish. Hypanthium sessile or nearly so, 

 8-4-angled, adnate to the ovary. Sepals 3-4, broad. Petals wanting. Stamens 3-4, in- 

 cluded. Ovary 3-4-celled. Stigmas 3-4, cylindric or conic- subulate. Ovules solitary in 

 each cavity. Nut-like fruit bony or crustaceous, 3-4-angled, 3-4 celled. Seeds 3-4 in each 

 fruit, cylindric. MERMAID-WEED. 



Leaves all nearly alike : sepals obtuse : fruit with obtuse angles. 1. P. pectinata. 



Leaves of 2 kinds; submerged and emerged, different: sepals acute: fruit with acute angles. 2. P. palustris. 



1. Proserplnaca pectinata Lam. Stems decumbent and creeping, 1-4 dm. long, 

 simple or branched : leaves all nearly alike ; blades pectinate or pectinate-pinnatifid, 1-3 

 cm. long, the segments linear or filiform, entire or sparingly toothed, acute : flowers ses- 

 sile or nearly so : sepals ovate, obtuse, persistent, erect : petals wanting : fruit ovoid-pyra- 

 midal, 3.5-4 mm. long, the angles rather obtuse, the faces transversely wrinkled or 

 slightly tuberculate. 



In pools and wet sandy soil, Massachusetts to Florida and Louisiana. Spring to fall. 



2. Proserpinaca palustris L. Stems decumbent at the base, rooting, 2-7 dm. long, 

 sometimes branched : leaves usually of 2 kinds ; blades linear to elliptic or oblong, often 

 varying to broadest above or below the middle, the submerged ones coarsely serrate or 

 pectinate, the segments entire or serrulate, the emersed leaves more entire, usually merely 

 serrate : flowers sessile, often clustered : sepals triangular, acute, ascending or converging : 

 petals wanting : fruit pyramidal or ovoia-pyramidal, 3 mm. long, the angles acute, the 

 faces concave, more or less distinctly tuberculate. 



In ponds, ditches and slow-flowing streams, New Brunswick to Iowa, Florida and Central America. 

 Spring to fall. Also in the West Indies. 



2. MYRIOPHYIiLUM L. 



Aquatic, often delicate herbs, with glabrous foliage. Stems commonly floating. 

 Leaves alternate or whorled, the emersed ones with entire toothed or pectinate blades, the 

 submersed ones with pectinate blades, their segments more delicate than those of the 

 emersed. Flowers usually monoecious, minute, axillary or often in terminal spikes, the 

 upper ones commonly staminate, with a short hypanthium, 2-4 sepals, or these obsolete, 2-4 

 petals and 4-8 stamens ; intermediate flowers generally perfect ; lower ones pistillate, with 

 a 4-grooved hypanthium, 4 minute sepals, 4 small petals, or these wanting, and a 4-celled 

 or rarely 2-celled ovary, with 2-4 often plumose stigmas and 1 ovule in each cavity. Fruit 

 bony, at maturity splitting into 2 or 4 angled, smooth or tuberculate nutlets. Seed soli- 

 tary in each nutlet. WATER MILFOIL. 



Emersed leaves or bracts minute, shorter than the flowers. 1. M. laxum. 

 Emersed leaves or bracts much longer than the flowers. 



Carpels essentially smooth. 2. M. vertitiUatum. 

 Carpels 2-keeled and roughened on the back. 



Slender : emersed leaves pectinate or pectinate-serrate. 3. M. pinnatum. 



Stout : emersed leaves nearly entire or serrate. 4. M. helerophyttum. 



1. Myriophyllum laxum Shuttl. Slender, 2-8 dm. long. Leaves in whorls of 4's, 

 of two kinds, the submersed ones ones 1-3 cm. long, rather crowded, the hair-like seg- 

 ments in about 3-5 pairs, the emersed leaves minute, less than 1 mm. long, .spatulate, 

 entire or nearly so : spikes 1-2 cm. long, delicate : flowers longer than the subtending 

 leaves, nearly 1 mm. long : fruit minutely warty. 



In ponds and lakes, middle and western Florida. Summer. 



2. Myriophyllum verticillatum L. Slender, 2-12 dm. long. Leaves of 2 kinds, 

 the submerged in whorls of 3's or 4's, rather crowded, 2.5-3.5 cm. long, the hair-like seg- 

 ments in about 10 pairs, often minutely roughened, the emersed leaves, or bracts smaller, 

 5-10 mm. long, pectinate-pinnatifid : spike 4-15 cm. long, erect : flowers shorter than the 

 bracts : staminate flowers about 2-2.5 mm. broad, with 4 purple hooded petals and 8 

 stamens : fruit smooth or nearly so, 2-2.5 mm. long, enlarged below the middle. 



In still water, Quebec to Minnesota, California and Florida. Also in Europe and Asia. Summer. 



3. Myriophyllum pinnatum (Walt.) B.S.P. Slender, 1-2 dm. or sometimes 6 dm. 

 long. Leaves in whorls of 3's to 6's, of two kinds, the submersed ones rather crowded, 1-2 

 cm. long, the hair-like segments usually in 3-5 pairs, the emersed leaves linear, shorter 

 than the submersed, pectinate or serrate-pectinate : spike erect, 6-20 cm. long, simple : 

 flowers shorter than the bracts, the staminate about 2.5 mm. broad, with 4 purple petals 



