fOTAMCAl. 

 THE OAtiiiaM 



JOURNAL OF BOTANY 



BRITISH AND FOREIGN. 



POTAMOGETON NITENS Weber, f. INVOLUTA. 



By Alfred Fryer. 



(Plates 353 & 354.) 



Potamogeton NITENS Weber, forma involuta milii. Bootstock with 

 stout far-creeping stolons, titem terete, simple below, much branched 

 above, 1-5 ft. long. Lower leaves semi-amplexicaul, lonfiitudinally 

 involute, broadest at the base, tapering gradually to the apex, 

 many-ribbed, with coarse often prominent ascending reticulations. 

 Upper leaves coriaceous, lanceolate, elliptical, oval, or spathulate, 

 with flattened petioles equalling or exceeding the lamina, produced 

 singly opposite, or in pairs subtending, the peduncles, abundant on 

 both flowering and barren branches. Stipules persistent, involute, 

 herbaceous or horny, blunt. Peduncles equal, often curved, shorter 

 than the subtending leaves. Flower-spike short, abortive, usually 

 with closed, rarely with open, flowers. Fruit imperfect, compressed, 

 keeled. Whole plant dark green, often with reddish stems. Probably 

 a hybrid between P. heterophyllus and P. perj'oliatus, or between the 

 latter and P. Zizii ? 



This Potamixjeton grows abundantly in Blackbush Drain and 



some adjacent ditches near Whittlesea, Cambridgeshire. It is 



distinguished from all other forms of P. nitens hitherto described 



c*^' by its involute stem-leaves, and by its very freely produced coriaceous 



c\« floating leaves resembling those of P. Zizii. When growing it may 



S easily be mistaken for that species, and in some of its states for P. 



I decipiens and P. heterophyllus ; in fact, it is in some degree a linking 



£>^ form between these three species and such obscure and doubtful 



^i— species as P. varians, P. falcatus, and P. coriaceus. 



p-) W^ithin its own limits f. involuta varies from the typical form 



1^^ figured in Tab. 351 to P. curvifolius Hartm. When growing in 



shallow water it approaches the No. 43 of Dr. Tiselius's Potamo- 



getones Suecici, P. nitens f. vadosa, but perhaps of all the nitens-iovms, 



issued in that beautiful publication our plant most nearly resembles 



No. 49, P. nitens e. innominatus, especially in the rare state with 



expanded flowers. 



JuuKNAL OF Botany. — Vol. 34. [Jan. 18i)G.] b 



