112 HALORAGACE^E. 



the lower part usually submerged. Flowers mostly solitary, sometimes 2 4 

 together, very small, nearly sessile. Stigmas purplish. 



Common Mermaid Weed. 



2. P. pectinacea Lam. : leaves all pinnatifid-pectinate ; fruit large, an- 

 gular, obtuse. P. palustris var. /? Mich. 



Sandy swamps. Mass, to Flor. Aug. 7J.. Distinguished from the former, 

 by having the leaves all finely pectinate and the fruit with rather obtuse in- 

 stead of acute angles. Pectinate Mermaid Weed. 



2. MYRIOPHYLLUM. Linn. Water Milfoil. 



(From the Greek pvptos, myriad, and <j>v\\ov, a leaf; in allusion to the minute 

 divisions of the leaf.) 



Flowers monoecious or rarely perfect. STERILE FL. Calyx 

 4-parted. Petals 4, ovate, sometimes inconspicuous or 

 wanting. Stamens 4 8. PERFECT FL. Calyx adhering to 

 the ovary ; limb 4-lobed. Petals none. Nuts 4, compressed 

 or subglobose, 1 -seeded. 



* Flowers octandrous. 



1. M. spicatum Linn.: leaves verticillate, pinnately divided, segments 

 capillary ; floral leaves shorter than the flowers ; lower subserrate and 

 mostly very entire ; petals broad-ovate ; carpels smooth and even. 



In water. Can. and N. S. Aug., Sept. 1J-. Stem slender, varying in 

 length with the depth of the water. Leaves in whorls, 35, pectinate. Flowers 

 in a terminal nearly naked spike. Spiked Water Milfoil. 



2. M. verticillaium Linn. : leaves verticillate, pinnately divided into ca- 

 pillary or setaceous segments ; floral leaves pectinate-pinnatifid, usually 

 much longer than the flowers ; petals oblong-obovate ; carpels smooth and 

 even. 



In water. Can. to Flor. W. to Texas and Oregon. July Sept. ^.St 

 long and stouter than in the preceding. Flowers in a terminal leafy spike, 

 upper ones sometimes perfect. Whorled Water Milfoil. 



** Flowers tetrandrous. 



3. M. heterophyUum Mich. : leaves verticillate, pinnately divided into ca- 

 pillary segments ; floral leaves ovate or lanceolate, sharply serrate, crowded ; 

 petals oblong ; carpels minutely roughened, slightly 2-ridged on the back. 



In water. Can. to Flor. W. to Texas. July. 1\.. Stem branching, thick. 

 Flcncers purple, whorled in the axils of the upper leaves. Stamens 4. (6, Mi- 

 chaux.) Various-leaved Water Milfoil. 



4. M. ambiguum NuU. : submersed leaves cut into capillary segments ; 

 the emersed ones pectinate ; floral leaves linear, tapering into a short peti< 

 ole, sparingly incised or toothed, sometimes entire ; flowers mostly perfect; 

 petals oblong; carpels smooth and even. M. capillaceum Torr. Comp. 

 M. procumbens Dig. 



Ponds and ditches. Mass, to Penn. July, Aug. Ij.. Stems 2 6 inches 

 long and creeping in the mud. or when floating in water, long and slender. 

 Leaves variously divided, depending upon the place of growth. ^Flowers small, 

 purplish. Polymorphous Water Milfoil. 



