POTAMOGETON.] NAIADACEAZ. 433 



often floating, stipules large long 2-winged or keeled, peduncle robust 



thickened upwards, spike stout, dry drupelets small turgid, beak short. 



Lakes, ponds, and streams, from Banff and Argyll to Devon and Kent ; Ire- 

 land ; fl. June-Sept. The largest British species, very lucid and glistening, 

 pale green. Stem 3-6 ft. Leaves 4-10 in., mostly submerged, very variable, 

 many-nerved, mostly serrulate towards the long or short tip; upper broader 

 rarely floating or coriaceous. Peduncles very variable in length ; spike 

 usually dense-fld. Drvpelets 1-10 in., convex on both faces, beak obtuse. 

 DISTRIB. Europe, N. Africa, N. Asia, N.W. India, N. America, 

 Australia. 



P. LU'CENS proper ; leaves shortly petioled, strongly serrulate apiculate or 

 mucronate, peduncles usually short. YAR. P. acumina'tus, Schum. (P. longi- 

 fo'lius, Gay) ; leaves very narrow tapering to both ends, peduncles more 

 than twice as long as the spike. 



Sub-sp. P. Ziz'n, Roth ; much branched, lower leaves often recurved, upper 

 cuneate at the base, floating obovate or oblong subcoriaceous, peduncles 

 very long, spike 1-2 in., drupelets more rounded. Forfar and Perth to 

 Hants and Surrey. The Lough Corrib plant, of which only one specimen is 

 known, and which was referred by Babington to P. longifolius, Gray, differs 

 in the narrower entire leaves and small scattered flowers. 



Sub-sp. DECIP'IENS, Nolte ; leaves sessile very variable suborbicular to oblong- 

 lanceolate mucronate subentire undulate, stipules short scarcely winged, 

 peduncles stouter, spike denser, drupelets smaller. 



fr * Flowering-stem with barren branches below ; leaves uniform, \- or wholly - 

 ampleocicaul , all submerged, oblong or ovate-oblong, upper opposite. 



9 P. Griffith'!!, A. Bennett ; stem terete, lower leaves subamplexicaul, 

 strap-shaped, tip concave, upper long-petioled oblanceolate tapering into 

 the petiole, stipules long narrow obtuse, peduncles slender, spike 

 dense-fld. 

 Wales, near Aber ; fl. summer. Stem, branched. Lower leaves 7-12 in., 11- 



nerved, with 4-5 fainter nerves near the midrib ; upper 13-17-nerved. 



Peduncles shorter than the upper leaves. Young drupelets ovoid, beak 



terminal from the ventral face. Habit between prcelon'gus and rufes'cens. 



10. P. prselon'gus, Wulfen. ; stem terete robust, leaves ^-amplexicaul 

 oblong obtuse entire 3-nerved tip usually concave, stipules large obtuse 

 not winged, peduncles very long stout, spike dense-fld., dry drupelets 

 large strongly acutely keeled. 



Lakes and deep rivers, chiefly in the E. ; Caithness to Essex and Salop ; 

 ascends to 2,800ft. in Perthshire; rare in Ireland ; fl. May-July. About 

 as large as P. lu'cens, but barren branches few. Stem greenish-white. Leaves 

 3-10 by 1-1| in., linear-oblong, midrib dilated, upper opposite, nerves 

 numerous and close. Peduncles hardly thickened upwards. Drupelets twice 

 as large as in P. lucens. DISTRIB. Europe (Arctic), Himalaya, America. 



11. P. salicifo'lius, Wolfg. ; stem slender terete, leaves all translucent, 

 submerged ^-amplexicaul lanceolate acute or subacute entire, stipules 

 obtuse, peduncles not enlarged upwards, spike short, dry drupelets 

 compressed rounded obtuse. P. lithuan'iciis, Gorski. 



F F 



