HALORAGIDACEAE ( WATER MILFOIL FAMILY) 603 



Petals small or none. Stamens 1-8. Fruit indehiscent, 1— 4-celled, with a 

 single anatropous seed suspended from the summit of each cell. Embryo in 

 the axis of fleshy albumen; cotyledons minute. 



1. Myriophyllum. Flowers monoecious or polygamous, the parts in fours, with or without 



petals. Stamens 4 or 8. Leaves often whorled, the immersed commonly pinnately 

 dissected. 



2. Proserpinaca. Flowers perfect, the parts in threes. Petals none. Leaves alternate, the 



immersed pinnately dissected. 



3. Hippurls. Flowers apetalous. Stamen and style only one. Leaves entire, whorled. 



1. MYRIOPHYLLUM [Yaill.] L. Water Milfoil 



Flowers monoecious or polygamous. Calyx of the sterile flowers 4-parted, 

 of the fertile 4-toothed. Petals 4, or none. Stamens 4-8. Fruit nut-like, 

 4-ceIled, deeply 4-lobed ; stigmas 4, recurved. — Perennial aquatics. Leaves 

 crowded, often whorled ; those under water pinnately parted into capillary 

 divisions. Flowers sessile in the axils of the upper leaves, usually above water, 

 in summer ; the uppermost staminate. (Name from ixvpioi, numberless, and 

 (pvWov, a leaf, alluding, like Milfoil, to the innumerable divisions of the leaves.) 



a. Flowering stems leaiV ; foliage leaves pectinate 6. 



b. Flowers in terminal naked spikes or in the axils of greatly reduced or 

 modified leaves c. 

 c. Leaves in definite whorls d. 

 d. Leaves 5-12 mm. long ; flowers chiefly 1 or 2 at each node of the 



spike ' 1. M. altemiflorum. 



d. Leaves chiefly longer ; flowers numerous, in remote verticels e. 

 6. Verticels apparently naked, the floral leaves shorter than or 

 only slightly exceeding the flowers. 

 Ehachis and segments of the foliage leaves capillary and of 



uniform diameter ; floral leaves entire or merely dentate . 2. M. »picafum. 

 Ehachis flattish and somewhat broader than the segments of 



the foliage leaves ; floral loaves pectinate . (3) J/", verticillatum, v. pectinatwn. 

 e. Verticels subtended by elongate floral leaves /. 

 /. Petals quickly deciduous ; st-amens 8 ; carpels plump and 



rounded on the back Z. M. verticiUatum. 



f. Petals tardil_v deciduous; stamens 4; carpels 1-2-ridged or 

 -angled on the back. 

 Floral leaves ovate to oblanceolate ; carpels papillose- 

 roughened 4. 3f. heteropTiyllum. 



Floral leaves linear or linear-lanceolate ; carpels smooth . 5. M. hippuroides. 

 c. Leaves variously arranged (verticillate, falsely verticillate, oppo- 

 site, or alternate) on the .^ame plant. 

 Carpels with flat sides and tuberculate-ridged back . . .'6. M. scabratuin. 

 Carpels plump, smooth or minutely papillose . . . , %. M. humile. 



b. Flowers in the axils of unmodified foliage leaves. 



Carpels smooth or barely papillose, plump, not ridged on the back . 8. M. humile. 

 Carpels \\ith flat sides and prominent tuberculate dorsal ridges. 



Fruit -2-2.5 mm. long 1. M. Fatncellii. 



Fruit 1-1.5 mm. long 6. J/, scabiatum. 



a. Flowering stems naked or with few scattered filiform uncleft leaves . 9. M. tenellum. 



§ 1. PENTApTERIS DC. Stamens 8 : petals early deciduous ; leaves ichorled. 

 * Floral leaves (bracts) scattered ; flowers rarely in verticels. 



1. M. altemifl5rum DC. Very slender ; leaves 5-12 mm. long, the rhachis 

 and segments capillary ; floicers solitary or in paira, in simple or branched 

 nearly naked spikes ; lowermost bracts pectinate, the others entire or nearly so, 

 shorter than the flowers. — Ponds and slow streams, Nfd. to Ont., s. to Middlesex 

 Co., Ma.ss., and L. Champlain, Vt. (Greenl., Eu.) 



* * Floral leaves and flowers in verticels. 



2. M. spicatum L. Leaves somewhat rigid, 1-3 cm. long, the rhachis and 

 capillary segments of uniform diameter; flowers verticillate, in an interrupted 

 apparently naked spike; the bracts shorter than or slightly exceeding the flower.s. 

 entire or merely dentate ; stigmas roundish, closely sessile, not elongated ; sepale 



