11 2 HYDROCHARITACE&. [ HYDRILLA, 



entire or 2-leaved spathe ; MALE flowers: stamens 3-12, in 1-4 

 series, anthers 2-celled. FEM. flowers : Solitary. Perianth 

 superior. Sepals 3, green or petaloid. Petals membranous or 

 none. Ovary 1-celled, inferior ; placentas 3-6, parietal or intruded 3 

 and sometimes almost meeting at the axis ; styles or style-arms 

 3-12; ovules many on each placenta, anatropous or orthotropous. 

 Fruit globose or ovoid, dry or pulpy, rarely dehiscent. Seeds 

 few or many, albumen none, embryo smooth or lineate. Species 

 about 50, in tropical and temperate regions of the world, some of 

 them marine. 



Stems branching, leafy ; leaves small ; spathes 

 small, sessile : 



Leaves whorled or the lower ones opposite ; 



styles undivided ; ovules anatropous . 1. Hydrilla. 



Leaves scattered, fascicled or somewhat whorl- 

 ed ; styles notched ; ovules orthotropous . 2. Lagarosiphon.. 



Stems none, or with stolons only, or a creeping 

 rootstock : 



Leaves all long, narrow and sessile ; male 

 scapes several-fld. : 



Perianth single . . . . .3. Vallisneria. 



Perianth double . . . . .4. Blyxa. 

 Leaves mostly or all petioled : 



Ovary not beaked ; fruit without wings ; 



leaves all petioled ; male scapes 2-3*fld. . 5. Hydrocharis. 



Ovary beaked ; fruit winged, submerged ; 

 leaves narrow, the floating ones long- 

 petioled ; flowers solitary . . .6. Oitelia. 



1. HYDRJLLA Rich. ; Fl. Brit. Ind. v, 659. 



A submerged leafy freshwater herb. Leaves short, usually 

 opposite below, 3-4-nately whorled above. Flowers minute,, 

 dioecious, the males shortly pedicelled, solitary in a subglobose 

 muricate spathe ; females sessile, 1-2 in a tubular 2-toothed spathe. 

 MALE flowers : Sepals 3, ovate or obovate, green. Petals 3, oblong 

 or cuneiform. Stamens 3 ; anthers large, reniform, opening elasti- 

 cally. Pistillode minute. FEM. flowers : Sepals 3, linear, green ? 



