241 
Floral leaves reduced to minute bracts. 4. M. tenellum. 
Flowers on both emersed and submersed stems. 
5. . humile. 
Flowers on submerged stems. 6. M. proserpinacoides. 
Carpels ridged or rough. 
Flowers on emersed spikes. 
Floral leaves ovate or lanceolate, serrate or entire. 
7. M. heterophyllum. 
Floral leaves linear-lanceolate, serrate. or entire. Pacific 
coast plants. ~ 8. M. hippurotdes. 
Floral leaves linear, pectinate toothed. 9. WZ. prnnatum, 
Floral leaves pinnately parted, longer. 
10. WM. Mexicanum. 
Floral leaves reduced to minute, nearly entire, spatulate 
bracts. 11. M. laxum. 
Flowers on submerged stems. 12. M. Farwellit. 
1. M. spicatum. L. Sp. Pl. 992 (1753). | 
Submerged leaves in whorls of fours and fives, the capillary 
divisions usually coarser than in No. 2 and No. 3. 
Floral leaves ovate, entire or toothed, commonly shorter than 
the flowers, sometimes none, leaving the spike nearly or quite 
naked. Spike 3-7 cm. in length. Petals four, deciduous. Stamens 
eight. Fruit 234 mm. long and 2-3 mm. broad. Carpels 
rounded on the back, with a deep, wide groove between them. 
Very rarely the carpels are somewhat rugose. A deep water 
plant. 
Common in Canada from Bear Lake to Newfoundland, New 
England to Minnesota, Utah and California, south to Florida. 
Common in Europe. : 
2. WM. alterniflorum. DC. FI. Fr. Supp. 529 (1805). Prod. 
3, 68 (1828). 
Submerged leaves usually in whorls of threes and fives, occa- 
sionally scattered, 6-10 mm. long, eight to ten pairs of pinne, 
the whole outline of stem and leaves narrow, 5-15 mm. in width. 
Spikes short, 3-5 cm. long, numerous on the branching stems. 
Uppermost floral leaves minute, ovate or linear, entire or minute- 
ly toothed, smaller than the flowers, early deciduous, leaving the 
fruiting spike naked. All the uppermost floral leaves and _ 
