In lakes in n.e. Tex., Apr-June; a highly variable circumpolar species that 

 occurs in N.A. from Nfld. to B.C., s. to Ut. and n.e. Tex. 



Plants referred here are typical in regard to leaves and floral bracts, but their 

 fruits are atypical in that they closely resemble those of M. heterophyllum. These 

 plants may eventually be found to represent a completely new entity. The closely 

 spaced whorls of leaves readily separate this species from M. spicatum, to which 

 it is referred by some authors. 



5. Myriophyllum heterophyllum Michx. Fig. 570. 



Stems rather stout; leaves whorled, in fours to sixes, the submersed pinnate 

 leaves 2-5 cm. long and with 7 to 10 flaccid capillary divisions on each side, the 

 divisions to about 2 cm. long, the amphibious leaves pinnatisect; emersed leaves and 

 bracts firm, lanceolate or spatulate-lanceolate to elliptic, entire or serrate, to 3 cm. 

 long and 1 cm. wide; spikes emersed, to 4 dm. long, usually much shorter; flowers 

 in whorls of 4 to 6, perfect or with the lower pistillate and the upper staminate; 

 bracteoles ovate, acuminate, serrate, 1-1.3 mm. long, 0.5-0.7 mm. wide; petals 

 (of staminate flowers) acutish, 1.5-3 mm. long; anthers 4, to 2.5 mm. long; fruit 

 subglobose, 1-1.5 mm. long and wide, minutely papillose, with the carpels 2-ridged 

 on the back but rounded on the sides and prominently beaked. 



In ponds, lakes and streams, in s. Okla. (Murray and Pushmataha cos.) and 

 mainly on the Edwards Plateau and in s.e. Tex., Apr.-Aug.; from Fla. to Tex. and 

 N.M., n. to N.D.., Ont. and s.w. Que. 



A large-bracted form of this species occurs in southeast Texas. 



6. Myriophyllum pinnatum (Walt.) B.S.P. Green parrot's-feather. Fig. 571. 



Plant variable, either submersed or essentially terrestrial; stems rooting in mud 

 freely branched or becoming much-elongated when growing in water; leaves in 

 whorls of 3 to 5 or subverticillate or commonly scattered, to about 3 cm. long, the 

 submersed leaves with about 5 or more short or somewhat elongate remote capil- 

 lary divisions on each side; emersed leaves linear to oblanceolate, pectinate or 

 sharply serrate, to 2 cm. long; flowers in the axils of the emersed leaves, perfect 

 or unisexual; bracteoles bluntly triangular, about 1 mm. long; petals purplish, 1.5-2 

 mm. long, rounded above, with a short claw; anthers 4, about 1 mm. long; fruit 

 pale, ovoid, 1.3-1.8 mm. long, the carpels with flat sides and 2 tuberculate dorsal 

 ridges. M. scahratum Michx. 



In swamp forests, on muddy shores or in shallow waters in e. Okla. (McCurtain, 

 Ottawa and Sequoyah cos.) and on the Edwards Plateau and in e. and s.e. Tex., 

 Mar.-June; from Fla. to Tex., n. to s. N. E., W. Va., Ky., 111. and la. 



Fam. 97. Hippuridaceae Link Mare's-tail Family 



Aquatic or amphibious plant with simple, sessile, whorled, entire leaves and 

 minute flowers in the upper axils to form a long terminal spike; flowers pistillate 

 or perfect, epigynous; hypanthium completely enclosing the ovary and bearing at 

 its summit in the perfect flowers a single stamen with short filament and large 

 2-celled anther; sepals and petals none; ovary 1 -celled and 1-ovuled, terminated by 

 a filiform style; fruit hard, indehiscent, nutlike, 1 -seeded. 



A monogeneric family. 



1. Hippuris L. Mare's-tail 



Characters of the family. A monotypic genus or sometimes as many as 3 species 

 are recognized. 



1208 



