POTAMEjE. 
323 
Nuts not exceeding 1 line in length. — Stagnant peaty water. 
P. VI. VII. » 
4. P. rufescens (Schrad.) ; submersed I. lanceolate narrowed 
at both ends subsessile membranous pellucid entire not apiculate, 
floating 1. subcoriaceous obovate obtuse narrowed into a short 
petiole, stip. without wings, nuts acutely keeled, peduncles equal. 
— E. B. 1286. P. fiuitans Sm.— St. simple. Upper 1. alone 
slightly coriaceous, often tinged with purple, longer than their 
stalks ; submersed 1. all nearly, if not quite, sessile. — P. spathu- 
latus (Schr.) differs from this by having long stalks to all its leaves 
and the upper ones truly coriaceous. Is it a native ? — Ditches 
and slow streams. P. VII. 
5. P. heterophyllus (Schreb.) ; submersed I. lanceolate narrowed 
at both ends sessile denticulate and apiculate, floating 1. subcori- 
aceous elliptical stalked, stip. broadly lanceolate obtuse with 2 
stout prominent ribs, lower ones linear-lanceolate, nuts obtuse on 
the back, peduncles swelling upwards. — E. B. 1285. P.gramineus 
Fries, Koch, Linn. ? — St. much branched below. Lower stip. 
without the two strong ribs and equally nerved, upper ones 
widely spreading. Dry nut slightly marked with 3 ridges on the 
back. — P. nitens (Weber) has the submersed 1. rounded and 
clasping at the base and the floating 1. more coriaceous. — Ponds 
and ditches. P. VI. VII. 
6. P. lanceolatus (Sm.) ; submersed I. lanceolate sessile nar- 
rowed at both ends entire not apiculate, floating 1. subcoriaceous 
elliptic-lanceolate stalked, stip. linear-lanceolate acute uppermost 
broader, nuts , peduncles equal. — E. B. 1985. — St. very slen- 
der, slightly branched, floating 1. not always present. Upper- 
most stip. apparently with 2 stronger dorsal ribs. Nuts un- 
known. — Streams, rare. Rivulet between Bodafon and Lligwy, 
Anglesea. Angus. Kincardineshire. Elgin. P. VII. VIII. E. S. 
** L. all submersed, membranous, lanceolate or broader ; 
stipules free. 
7. P. lucens (L.) ; I. pellucid oval lanceolate stalked denticu- 
late and apiculate, stip. winged, nuts " obtuse on the back and 
slightly keeled when fresh," peduncles swelling upwards, spikes 
cylindrical densely flowered.— iE. B. 376.— Combined by some 
authors with P. heterophyllus, but appears to be sufficiently di- 
stinct. All the stipules have two prominent wings on their back 
and are longer and narrower in proportion. Spikes long, about 
equalling the peduncles. According to Mr. W. Wilson " ovate- 
lanceolate moderately acute coriaceous 1." sometimes occur, but 
I suspect the existence of another species. — A variety is occa- 
sionally found with the limb of the 1. much reduced in size and 
the midrib prominent and resembling a long spine, which is, ac- 
