260 Key to the System of 



1192. Leaves scattered. 



Dwarf; leaves very small, linear-cylindrical; flowers minute; 

 stamens two to four ; hairlets of stigmas very minute ; 

 fruit-calyx lobeless ; fruitlets four, generally smooth. 



M. integrifoliuni. 



Leaves opposite ... ... ... ... ... 1193 



1193. Leaves from broad- to narrow-linear. 



Dwarf ; leaves small ; staminate flowers generally stalked ; 

 stamens eight; hairlets of stigmas rather long; fruit-calyx 

 short-fourlobed ; fruitlets four, rough. 



M. pedunculatum. 



Leaves from oval to narrow-elliptical. 



Mostly creeping and semi-aquatic ; leaves very small, rarely 

 trilobed ; staminate flowers generally sessile ; stamens 

 eight ; fruit-calyx short-fourlobed ; fruitlets four, smooth. 



M. amphibium. 



1194. Emerging leaves entire ... ... ... ... 1195 



All leaves capillary-pinnatisected ... ... ... 1196 



1195. Emerging leaves filiform-linear. 



Stems and branches usually elongated ; leaves whorled, 

 lower submerged leaves divided into long capillary 

 segments, the upper gradually short-lobed or merely 

 denticulated ; stamens eight ; fruitlets four, often rough. 



M. variifolium. 



Emerging leaves from oval to narrow-elliptical. 



Stems and branches usually elongated ; leaves whorled, 

 the submerged leaves nearly all divided into long capillary 

 segments ; stamens eight ; fruitlets four, often smooth. 



M. elatinoides. 



1196. Leaves whorled. 



Stems and branches rather short ; leaves comparatively 

 small, often greyish-green ; emerged leaves oval in outline, 

 pinnatifid ; stamens eight ; fruitlets four, very small, 

 rough. M. verrucosum. 



Leaves nearly all simply opposite. 



Stems and branches elongated, dotted ; some of the leaves 

 not seldom ternately whorled ; staminate flowers stalked, 

 supported by a conspicuous petaloid marginally converging 

 bract ; stamens eight ; fruitlets four, smooth. 



M. Muelleri. 



