100 Key to the System of 



489. Fruitlets normally four, each provided with a long 



thin stalk-like stipes. 



Aquatic plants ; leaves along the branches, always very 

 narrow, alternating ; flowers in spikes or almost headlets, 

 or few or two, at or near the upper end of a threadlike 

 often much elongated and spirally twisted stalk ; bracts, 

 sepals and petals absent ; stamens and pistils in the same 

 flowers ; stamens two ; anthers much bilobed ; stigma 

 almost sessile, undivided ; fruitlets four, very small, 

 oblique. Ruppia. 188T 



Fruitlets spikelike arranged within the lower portion 

 of a clasping floral leaf. 



Oceanic plants ; leaves along the branches, always narrow, 

 alternating ; flower-spikes unilateral ; sepals and petals 

 none ; stamens and pistils in distinct flowers ; stamen 

 one ; anther sessile ; stigmas two, capillary ; fruitlets 

 single. "Grass-Wrack." Zostera* 1888 



490. Fruit simple. 



Aquatic plants ; stem slender ; leaves along the branches, 

 constantly narrow, often opposite ' ( or whorled and den- 

 ticulated ; flowers solitary, axillary ; stamens and pistils 

 in distinct flowers ; calyx small, somewhat tubular, very 

 tender ; stamen one ; anther sessile ; stigmas two to four ; 

 ovule one ; fruit often connate with the calyx. 



Najas. 1889 



Fruit compound ... ... ... -. ... 491 



491. Leaves threadlike-linear. 



Aquatic plants, always very slender ; leaves along the 

 branches ; flowers within a clasping bract ; calyx quite 

 minute, three-lobed ; stamens and pistils in distinct 

 flowers ; stamens three ; anthers connate ; style elon- 

 gated ; stigma one ; fruitlets three, on short stalklets. 

 Figure 120. (Lepilaena.) Althenia. 1890 



Leaves often broad-linear. 



Oceanic plants ; leaves alternate or crowded in two rows, 

 always narrow ; flowers solitary, within the clasping 

 base of a leaf ; stamens and pistils in distinct flowers ; 

 stamens two, quite connate ; anthers narrow, four-celled ; 

 united filaments elongated or abbreviated ; ovularies two, 

 disconnected ; ovule one ; style ending in a bifid stigma ; 

 fruitlets two, small. Cymodocea. 1891 



