Genus i. 



PONDWEED FAMILY. 



85 



28. Potamogeton gemmiparus (Robbins) Morong. 



Fig. 201. 



Potamogeton pusillus var. ( ?) gemmiparus Rob- 

 bins in A. Gray, Man. Ed. 5, 489. 1867. 



Potamogeton gemmiparus Morong, Coult. Bot. 

 Gaz. 5 : 51. 1880. 



Stems filiform, terete, branching, 5-4° long. 

 Leaves capillary, sometimes not as wide as the 

 stem, often with no perceptible midrib, taper- 

 ing to the finest point, 1/-3' long, 2-glandular 

 at the base; stipules i'-i' long, acute or obtuse, 

 mostly deciduous; spikes interrupted, 3-6-flow- 

 ered; peduncles filiform or sometimes slightly 

 thickened, ¥-2' long; fruit seldom formed, 

 similar to that of P. pusillus. 



In ponds, eastern Massachusetts and Rhode 

 Island. It is commonly propagated by its abun- 

 dant buds, the leaves and stems are often alike 

 in thickness so that the plant seems to consist 

 of threads. Aug.-Sept. A very slender form of 

 the preceding and doubtfully distinct from it. 



Thread-like Pondweed. 



29. Potamogeton diversifolius Raf. Rafinesque's Pondweed. Fig. 202. 



Potamogeton hybridus Michx. Fl. Bor. Am. i : 

 101. 1803. Not Thuill. 1790. 



Potamogeton diversifolius Raf. Med. Rep. (II.) 

 5: 354. 1808. 



Potamogeton diversifolius multidenticulatus Mo- 

 rong, Mem. Torr. Club, 3: Part 2, 48. 1893. 



Potamogeton diversifolius trichophyllus Morong, 

 Mem. Torr. Club, 3 : part 2, 49. 1893. 



Stems flattened or sometimes terete, much 

 branched. Floating leaves coriaceous, the 

 largest 1' long by 1' wide, oval or elliptic and 

 obtuse, or lanceolate-oblong and acute ; petioles 

 generally shorter, but sometimes longer than 

 the blades, filiform or dilated; submerged 

 leaves setaceous, seldom over I" wide, 1/-3' 

 long; stipules obtuse or truncate, 3"~s" long, 

 those of the floating leaves free, those of the 

 submerged leaves sometimes adnate; emersed 

 peduncles z"~7" l° n !=; submerged peduncles 

 2"-3" long, clavate, as long as the spikes ; 

 emersed spikes 3"-s" long, occasionally inter- 

 rupted; fruit cochleate, rarely over i" long, 

 3-keeled, the middle keel narrowly winged and usually with 7-12 knob-like teeth on the mar- 

 gin, the lateral keels sharp or toothed ; embryo coiled ii times. 



In still water, Maine to Florida, west to California and Texas. June-Sept. A common and 

 well-marked species which often covers large areas of water, practically to the exclusion of every- 

 thing else. From P. dimorphus, its nearest relative, it may readily be distinguished by its distinctly 

 stalked submerged spikes of flowers. 



