442 Key to the System of 



Leaves sharp-pointed. 



Branches strongly compressed ; leaves all submerged, 

 membranous, transparent, scattered except the uppermost, 

 their longitudinal venules five or more ; stipules acute ; 

 flowers usually few in the spike ; fruitlets straight- 

 attenuated at the summit, prominently angular at the 

 outer margin, their style recurved. P. acutifolius. 



1885. Fruitlets conspicuously longer than broad. 



Branches thread-like ; leaves all scattered, submerged, 

 narrow-linear, pointed ; flowers usually few and some- 

 what separated in the spikes ; fruitlets when dry almost 

 semiorbicular and then prominently biangular near the 

 outer margin, their style almost terminal. 



F. pectinatus. 



Fruitlets hardly longer than broad. 



Branches thread-like ; leaves all submerged, thinly linear - 

 filiform ; flowers in the spikes often somewhat whorled ; 

 fruitlets very small, when dry almost orbicular, but 

 laterally truncate, blunt at the outer margin, their style 

 distinctly lateral. P. filiformis. 



POSIDONIA. 



1886. Connective of the anthers gradually pointed. 



Submerged stem and branches long, in their lower portion 

 much beset with the fibrous remnants of decayed foliage ; 

 leaves firm, broad-linear, rounded-blunt, shining, their 

 venules numerous, subtile ; spikes approximated, jointly 

 stalked ; flowers quite small, few or several in each spike ; 

 sepals from ovate to orbicular, fixed beyond their base ; 

 connective much longer than the anther cells ; stigma 

 capillary -tuf ted ; fruitlet lanceolar - ellipsoid, oblique, 

 carnulent, without any stalk-like basal elongation, large- 

 seeded. P. Australis. 



RTJPFIA. 



1887. Stalk-like elongations thin, but rigidly straight, much 



longer than the fruitlets. 



Submerged, preferring brackish waters ; stem and branches 

 very slender, often elongated ; leaf -stalks clasping, some- 

 what turgid ; leaves rather long ; anthers almost sessile, 

 their lobes from ellipsoid to globular ; fruitlets turgid 

 towards the base, much attenuated towards the almost 

 pointed summit. R. maritima. 



