821 



ON A NEW HYBRID POTAMOGETON OF THE 



FLUITANS GROUP. 



By Alfred Fryer. 



(Plate 299.) 



Potamogeton crassifolius mihi = P. Zizii x P. natans. — 



Eootstock with thick stolons, rooting deeply in the soil ; stem 4-5 ft. 

 long, very stout, round, simple below, branched above with simple 

 branches; leaves all stalked, coriaceous, opaque when mature; lower 

 leaves reduced to submerged phyllodes, or narrowly lanceolate and 

 tapering into the petiole, or with a distinct lanceolate lamina, all 

 thick and coriaceous like the upper ones ; distant, few in number, 

 usually all decayed by the time of flowering ; tipper leaves very thick and 

 fleshy, oblong-elliptical, or oval, with a prominent fold at the base of 

 the lamina, which is slightly decurrent, or rarely lanceolate and 

 gradually narrowed into the stalk; petiole jiat above, slightly enlarged 

 towards the apex, shorter than the lamina ; stipules not winged, not 

 channelled on the back, but with two conspicuous green ribs, horny 

 with scarious edges, or herbaceous, acute ; lowest sometimes bearing 

 a short phyllode, or more rarely a long lanceolate ordinary lower 

 leaf ; peduncles of equal thickness throw/bout, terminal becoming 

 lateral by growth of the branch, equalling or slightly exceeding the 

 stem in thickness, 2-3 times as long as the Sower- spike, much 

 shorter than the subtending leaves ; flower-spike cylindrical, dense, 

 1-1 J in. long, usually (always ?) barren, perianth-leaves closed at 

 the time of flowering, but the stigmas exserted ; colour of the whole 

 plant bright green, or with the young upper leaves sometimes reddish 

 or streaked with reddish purple. 



Potamogeton crassifolius differs in its parentage from P. fluitans 

 Roth, being a hybrid between forms of P. Zizii and P. nutans, 

 instead of between P. lucens and P. nutans. It varies slightly 

 from the type described above, because in different localities it origi- 

 nates from different forms of P. Zizii, and because the seed-parent 

 is sometimes Zizii and sometimes natans. The type of the species 

 (figured PI. 299) is a very robust plant, growing in deep water, and, 

 although springing from a single rootstock, spreading along the 

 water for a distance of 10 or 12 yards. In habit and general 

 appearance it closely resembles a large form of P. Zizii (P. coriaceus 

 v. major mihi), which grows in the same drain intermixed with 

 P. natans, and probably it is coriaceus $ x nutans $ . The upper 

 floating-leaves of coriaceus v. major and crassifolius so closely resemble 

 one another in some specimens that the plants are with difficulty 

 separable, except by examination of the widely different lower 

 leaves. In the Mepal Engine Drain, where three separate stations 

 have been found, P. crassifolius is always accompanied by P. Zizii, 

 and I have met with it in no locality where that species does not 

 exist. In another locality, — at Westmoor, in the parish of Dod- 

 dmgton, — some miles distant from the Mepal station, no doubt 

 about its parentage is possible, as only P. Zizii and P. natans are 



Journal of Botany. — Vol. 28. [November, 1890.] y 



