280 



©tiginal ^vttdts. 



POTAMOGETON ZIZII, M. & K., AS A BEITISH PLANT. 

 By Henry Trimen, M.B., F.L. S. 



(Tab. 204). 



Two critical pond-weeds allied to P. Jucens have been already 

 described and figured in this Journal — P. nitens, Web.,* and 

 P. decipiens, Nolte,! the description of the former having been 

 contributed by the lamented Dr. D. Moore. Attention is now 

 •called fo a third of these i)uzzling forms, P. Zizii, M. & K., which 

 occupies a position in some respects intermediate between P. luceiis 

 and P. heU'rophijllus, to both of which, as ^si\\ be seen by the syno- 

 nymy given below, it has been referred by competent authorities. 



It is only within the last few years that this variety has been 

 distinguished in England, and its name has not been determined 

 with certainty till the present season. We are chiefly indebted to 

 Mr. A. Brotherston for its discovery, and to his note in the Keport 

 for 1878 of the Botanical Locality Piecord Club, p. 18, | we may 

 refer, for some j^articulars. Mr. Brotherston' s locality is Caul- 

 shiels Loch, near Melrose, Eoxburghshire, where the plant grows 

 in shallow water (less than a foot deep in 1878, about two feet in 

 the present very wet year) ; and he sent out through the Exchange 

 Club, in 1878, specimens labelled " P. Zizii? " from this station. 

 Mr. Baker, in the Exchange Club Pieport,§ adds another locality 

 from Borrer's herbarium — Llyn Maclog, Anglesea, Wihon] and 

 two more may be now recorded from the British Museum her- 

 barium — the Teviot near Eoxburgh Castle, W. McPiitcliie (where 

 Mr. Brotherston assures me the plant is not now to be found ||) ; 

 and Balgarves Loch, near Forfar, 1837, J. H. Balfour (under the 

 name " P. rufescens / ") 



P. Zizii is one of those species of the genus which possess both 

 a form with floating leaves and one without them ; hence it some- 

 times bears a resemblance to P. heterophijllus, which usually 

 has them, and at others is like P. lucens, where they are very 

 rarely present. The British specimens of P. Zizii that I have 

 seen are all witliout any floating leaves, properly so called, but 

 the upper ones are yet very different from those lower down the 

 stem. The former are opposite and conspicuously stalked, the 



* ' Journ. Bot.', 1^04, p. 325, t. 23. f ' Journ. Bot.', 18G7, p. 71, t. Gl. 



I See p. 255 of this volume. § See p. 252 of this vohime. 



II A plant from this locality wliieh has been distributed by Mr. Brotherston, 

 through the Exchange Club, under tlie name of P. nitens, does not appear to me 

 lo be that species, but a large form of P. dcciinens approaching P. jyrcelongus ; 

 probably P. salicifoUus, Wolfg. 



s. N. VOL. 8. [October, 1870.] 2 p 



