372 



5. P. lu'cens, L. ; stem stout, leaves large all translucent 



linear- or oblong-lanceolate undulate serrulate, upper opposite often flouting, 



stipules large long -.i-winged, peduncles robust thickened upwards. 



Lakes, ponds, and streams from Aberdeen and Argyle to Devon and Kent ; tl. 

 July-Sept. The largest British species, very lucid and gli.-ti-nin^. pale 

 green. Stem 3-5 ft. Leaves 4-10 in., chiefly submerged, very variable. 

 many-nerved, most serrulate towards the long or short tip ; upper rarely 

 floating, broader. Peduncleg very variable in length ; spike stout, usually 

 dense-flowered. Drupes (dry) iV in., convex on both faces, beak obtuse. 

 DISTRIB. Europe, N. Africa, Siberia, Dahuria, N.W. India, N. America. 

 The following varieties are not constantly distinguishable. 



VAR. 1, lu'cenx proper ; leaves shortly petioled strongly serrulate apiculate 

 or mucronate, peduncles not twice as loug as the spike. VAH. '2. <ii-ni,iiiiii'tn.i. 

 Schum. (sp.) ; leaves shortly petioled narrow acuminate, peduncle more 

 than twice as long as the spike. VAR. 3, decip'iens, Nolte (sp.) ; leaves 

 sessile cuspidate serrulate at the tip, stipules shorter scarcely winged, 

 peduncles not twice as long as the spike. In a canal at Bath. 



P. lonyifo'lius, Gay, is referred by Gren. and Godr. rightly to /'. Im-riif, and 

 is no doubt its var. acuminatus. The Lough Corrib plant, referred by 

 Babington to Gay's longijolius, has much narrower not serrulate leaves, and 

 small scattered flowers ; only one specimen is known. 



*** Flowering stem with barren branches below ; leaves $ or w/iolli/ 

 all submt-ryed, uniform, oblong or ovate-oblowj, upper 



6. P. praelon'gus, Waff.; stem stout, leaves usually concave at the 

 tip 4' am pl ex i cau l obtuse 3-nerved, stipules large obtuse not winged, 

 peduncles long stout, spike stout, dry drupe sharply keeled. 



Lakes and deep rivers, chiefly on the East from Nairn to Berks and Surrey ; very 

 rare in Ireland ; fl. June-July. Almost as large as P. luceiis and much like 

 it in habit, but barren branches few. Stem terete. Leave* 3-9 in., 1-H in. 

 broad, linear-oblong, mid-rib dilated, its vascular bundles remote appear- 

 ing like a band of parallel fibres, upper opposite. Pedmirlf* usually longer 

 than the leaves, hardly thickened upwards. Spite usually dense-flow* iv I. 

 Drupe (dry) much as in P. lucent, but more sharply keeled. DISTIUB. 

 Europe (Arctic), Himalaya, America. 



7. P. perfolia'tus, L. ; stem stout, leaves ovate-cordate ainplexirau! 

 obtuse quite entire 5-7 -nerved, tip Hat, stipules small subacute disappear- 

 ing early, peduncles short stout, spike dense-flowered. 



Ponds, lakes, and streams ; ascending to 1,200ft. in Yorkshire ; fl. July-Sept. 

 Stem terete branches dichotomous. Leaves 1-2 in., upper opposite, 

 translucent. Peduncles terminal in the forks, axillary, not thickened up- 

 wards. Sepals long-clawed. Drupe (dry) ^ in., compressed, hardly keeled, 

 beak short. DISTRIB. Europe (Arctic), N. Africa, N.W. India, America. 



8. P. crispus, L. ; stem slender, leaves distichous ^-amplexicaul ob- 

 long acute or obtuse crisped serrulate 3-nerved, stipules small obtuse dis- 

 appearing early, peduncles tapering upwards curved, flowers few small. 

 Ponds, ditches, &c. from Elgin and Isla to Devon and Kent ; fl. July-Aug. 



Si- in dichotomously branched, compressed. Leavet li-3 in., cl<> 

 spreading or recurved. Peduncles stout or slender, la'xly 6-8-flowereA 

 Jtitipe (dry) J in., obliquely ovoid, acuminate, compressed, beak long. l)i.-- 

 TBIB. Europe, Siberia, India. 



