POTAMOGETOX.] NAIADES. 371 



or obovate-lanceolate membranous rarely suberect and emersed, upper float- 

 ing (var. fluitans) or erect, stipules large, peduncles slender, spike and 

 flowers smaller, dried drupe ^ in. red. P. oblonym, Viviani. Lakes and 

 pools, especially on heaths ; ascends to near 1,600 ft. in the Lake District. 



Sub-sp. PLANTAGIN'EUS, Ducros ; leaves all more membranous ovate or oblong 

 obtuse or cordate at the base, stipules shorter, peduncle more slender, dried 

 drupe ^ in. green. Local. 



Sub-sp. KIR'KII, S;/me ; lower leaves very narrow linear-lanceolate, upper 

 sometimes submerged long-petioled oblong-lanceolate, stipules very long. 

 P. sparganii/oiius, Bab. not Lsest. Ma'am, Co. Galway. 



2. P. rufes'cens, Schrad. ; leaves translucent, lower submerged linear- 

 lanceolate many-nerved, upper floating or erect rarely submerged broader 

 subcoriaceous, petiole short, stipules large, 'peduncle stout not enlarged 

 upwards, dry drupe ovoid acuminate. P. fluitans,. Sin, not 'Schrad. 

 Ponds, canals, and ditches from Isla and Caithness southwards ; ascends to 



1,500 ft. in the N. of England ; fl. 'July-Sept. Stems terete, 1-4 ft. Leaves 

 reddish, not toothed, upper 2-5 iii., obovate or oblong-lanceolate, obtuse ; 

 lower sessile. Stipules not winged, obtuse, very variable. 'Peduncle 2-5 in. ; 

 spike stout. Drupe (dry) red, ventral margin convex, dorsal ^-circular keeled. 

 DISTRIB. Europe (Arctic), Siberia, Dahuria, N.W. India", N. America. 

 The acuminate fruit is a good character for this species. 

 ** Floiceri-ng stem with copious barren branches beloic ; upper leaves floating, 



broader than the submerged lower ; peduncles axillary and terminal, tiiany- 



and dense-Jlowered. 



3. P. heterophyl'lus, Selireb. ; stem slender, submerged leaves linear- 

 lanceolate, stipules small, peduncles stout thickened upwards. 



Pools, lakes, &c., rather local, from Kent and Dorset northwards ; absent 

 from Ireland ; fl. July-Sept. Stem terete, 2-4 ft., green or reddish. Leaves, 

 submerged 1-3 in., sessile, flaccid, acuminate or cuspidate ; floating 0, or 

 similar, or oblong petioled and coriaceous. Peduncles axillary and terminal. 

 Jjrupe (dry) T >j in., ventral margin nearly straight produced into a short 

 beak, dorsal ^-circular 3-keeled. DISTRIB. Europe (Arctic). 



Sub-sp. HETEROPHYL'LUS proper ; leaves not amplexicaul almost flat, upper 

 opposite coriaceous floating. P. gramineus, Fries and Koch. 



Sub-sp. NI'TENS, Weber; (sp.) branches many rooting from the upper axils, 

 leaves alternate all submerged recurved undulate, peduncles less thickened 

 upwards, dried drupe smaller. Bute, Perth, Elgin, Nairn, and Ireland, very 

 rare. Foreign specimens (authentically named) approach P. perfoliatus. 



Sub-sp. ? LONCHI'TIS, Tuckerman (sp.); leaves more linear, usually all submerged 

 ^-amplexicaul straight 7-9-ribbed, upper long-petioled, peduncles slightly 

 thickened upwards (drupe obliquely obovate, unknown in Britain, hence 

 the identification is doubtful). P. salicifolius, Wolfg. ? River Boyne. 



4. P. lanceola'tus, Sm.; stem filiform fragile, leaves sessile straight 

 linear- or oblong-lanceolate obtuse, upper opposite sometimes floating 

 petioled, stipules slender acuminate, peduncles short not thickened upwards. 

 River Lligwey in Anglesea ; fl. July-Aug. Similar to slender forms of P. hetero- 



phylhis, but the leaves are darker green, very obtuse, usually narrower, 

 and the axillary spike is very short ovoid. Fruit unknown, though the plant 

 was discovered in 1808. Syme doubtfully refers the P. nigrescent of Fries' 

 Mantissa to this. Fries' Herb. Normale plant is quite different. 



B B 2 



