Page:Journal of botany, British and foreign, Volume 34 (1896).djvu/17

 THE JOUKNAL OF BOTANY BRITISH AND FOREIGN. POTAMOGETON NITENS Weber, f. INVOLUTA. By Alfred Fryer. (Plates 353 & 854.) PoTAMOGETON NITENS Weber, forma involuta mihi. Bootstock with stout far-creeping stolons. Stem terete, simple below, much branched above, 1-5 ft. long. Lowe}- leaves semi-amplexicaul, longitudinally 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, tJie 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. perfoliatus, or between the latter and P. Zizii ? This Fotamogeton grows abundantly in Blackbush Drain and some adjacent ditches near Whittlesea, Cambridgeshire. It is distinguished from all other forms of P. 7iitens hitherto described by its involute stem-leaves, and by its very freely produced coriaceous floating leaves resembling those of P. Zizii. When growing it may easily be mistaken for that species, and in some of its states for P. decipiens and P. heterophyllus ; in fact, it is in some degree a linking form between these three species and such obscure and doubtful species as P. varians, P.falcatus, and P. coriaceus. Within its own limits f. involuta varies from the typical form figured in Tab. 851 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-forms issued in that beautiful publication our plant most nearly resembles No. 49, P. nitens e. innominatus, especially in the rare state with expanded flowers. Journal of Botany, — Vol. 34, [Jan, 189G,] b