POTAMOGETON.] NAIADACE^ti. 435 



Forfar to York and Essex, local ; Co. Down ; fl. July-Aug. Stem broad, 

 internodes long. Leaves 4-10 in., often | in. broad, with 3 strong and many 

 slender nerves. Peduncles 2-3 in. ; spike many-fld. Drupelets in., slightly 

 compressed; beak terminal. DISTRIB. Europe, N. Asia, N. America. The 

 P. compres'sus, L., being a doubtful plant, the name zosterifo'lius is adopted 

 by most authors. 



16. P. acutifo'lins, Link; stem compressed, leaves ^-amplexicaul 

 linear finely acuminate 3-nerved, stipules lanceolate acute, peduncle rarely 

 equalling the very short spike, dry drupelets convex with a strong tooth 

 near the base ventrally, beak recurved. 



Lakes and ditches, Yorkshire to Kent and Dorset, rare ; fl. June-Aug. Stem 

 narrower than in P. zosterifolius. Leaves 2-6 in., with 3 strong and many 

 slender nerves. Peduncles f- (rarely) 1 in. ; spike about J in. Drupelets 

 in., compressed ; beak ventral. DISTRIB. Europe, Australia. 



17. P. obtusifo'lius, Mert. and Koch ; stem slender compressed, leaves 

 sessile linear subacute or obtuse 3-nerved, stipules very obtuse, peduncles 

 very short, spike small ovoid, dry drupelets broad keeled, beak straight. 

 P. gramin'cus, Sm., not L. 



Pools and ditches from Aberdeen to Hants and Kent ; Ireland, rare ; fl. July- 

 Aug. Stem flexuous, much branched, 4-gonous, not winged. Leaves 2-6 by 

 f- in., dark green, rather opaque, with no visible nerves between the 3 

 principal ones ; stipules ^ in., tip broad. Peduncles much shorter than the 

 leaves, terminal or in the forks, equalling or exceeding the densely few-fld . 

 spike. Drupelets compressed, broadly obliquely ovoid. DISTRIB. Europe, 

 W. Siberia, N. America. 



18. P. pusil'lus, L. ; stem filiform, leaves |-amplexicaul narrowly 

 linear acute acuminate or subacute 1-3- (rarely 5-7-) nerved, stipules 

 small acute, peduncles slender, spike few-fld., dry drupelets small turgid 

 obtusely keeled, beak stout. 



Rivers, ponds, and ditches, from Orkney southd. ; ascends to 1,000 ft. in the 

 Highlands; Ireland; fl. July-Aug. Stem often much branched, rarely 

 slightly compressed. Leaves |-3 by ^O~TO ^ n -> rarely acuminate, green, 

 rather opaque. Peduncle usually much longer than the 6-10-fld. spike ; 

 flowers minute. Drupelets obliquely ovoid ; beak subterminal. DISTRIB. 

 Europe (Arctic), N. Africa, N. Asia, N. America. 



P. PUSI1/LI7S proper ; leaves acute or subacute, 1-3-nerved. YAR. tenuis'siwa, 

 Koch (P. yrac'ilis, Bab., not Fries) ; smaller, leaves acuminate more 

 spreading 1 -nerved. VAR. riy'ida, A. Benn. ; rigid, fragile, lateral nerves 

 of leaf faint or 0, stipules long, spike \ in., drupelets obscurely keeled. 

 Orkney. 



Sub-sp. P. FRIES'II, Rupr. ; stem compressed, leaves often fascicled broader 5- 

 rareiy 7-nerved, peduncles 1-2 in. compressed, spike |-| in., interrupted, 

 dry drupelets larger, beak shorter. P mucrcna'tus, Schrad. ; P. compres'sus, 

 g m- Orkney to Dorset, local ; Sussex and Hants ; Co. Down. 



Sub-sp. P. STURROCK'II, A. Benn. ; stem filiform, leaves 2-3 in. subobtuse 3-5- 

 nerved bright-green pellucid, peduncles very slender 2-4 in., spike f-^ in., 

 dry drupelets much smaller, beak short. Forfar and Perth. A very elegant 

 and delicate plant. 



F F 2 



