158 J. O. HAGSTROM, CRITICAL RESEARCHES ON THE POTAMOGETONS. 



P. COlljUllgens n. sp. — Fig. 60, A—C; 61, E. 



' Caulis teres— subte res ramosus, ramis recurvatis ut in P. dimorpho, ramulis spi- 

 ciferis prolongatus, internodiis infimis brevibus, superioribus longioribus. Folia na- 

 tantia 11-nervia obtusa ovalia evaginata, petiolata, petiolo int'eriorum foliornm 

 lamina longiore, superiorum subbreviore, laminis 20 — 30 X 10 — 12 mm; submersa 

 angustissime linearia subobtusa vaginata lignlata 50 — 70 X 0,75 mm; ramulina breviora, 

 omnia inconspicue 3-nervia. Pedunclus brevis, 1—4 mm longus. Spicce densee, in- 

 fimse ca. S-florse, summse ca. 20-flor8e. Fructus parvus, 1,3 x 1 mm, rotundatus, a 

 latere compressus, erostratus tricarinatus carinis gibbosis. — 



This species has qualities reminding both of P. dimorpJius and of diversifolius. 

 Of the former remind the floating leaves with their rounded apexes and numerous 

 nerves, but the lower ones are longer petioled whereupon the stalk-length gradually 

 abates upwards. They are widest at the middle as is usually the case in P. diver- 

 sifolius, which, again, has the apexes shaped so that both the marginal lines meet 

 in a more or less acute angle. Submersed leaves of about the same length as in 

 P. diversifolius but more obtuse, however not so rounded at the top as in P. dimor- 

 plius, see the fig, 60, B! Sheaths and ligules, see above! Branches recurved as in 

 just mentioned species, but seldom (the uppermost) or never they terminate them- 

 selves by spikes as does P. dimorphus. Peduncles very short, the topmost only 

 3 — 4 (5) mm, in the two other species 10 — 15 mm. Fruit very small, a little shorter 

 than that of P. diversifolitis, which also has more prominent dorsal keel, by which 

 its fruit as well grows a little broader. Besides, the fruits of these two species 

 are extremely alike, both lacking a beak (like P. dimorphus) and possessing small 

 prickles on the dorsal and lateral keels (common to P. spirilliformis too), see the 

 fig. 60, CI The upper spikes are many-flowered; all richly fruiting, consequently it 

 should not be considered a hybrid in usual sense, though probably of a hybrid origin. 



The species has been mixed up with P. diversifolius, but differs easily from it 

 by the deviating floating leaves and short upper peduncles, the more obtuse sub- 

 mersed leaves and the more faintly keeled, smaller fruits. Full-numbered subepi- 

 dermal bast seems always to be present in the stem. 



Distribution N. America, Mexico, San Luis Potosi, 79, Schaffner (hb. Upp- 

 sal. et Lund.). Lancaster Co., Pa., 90, Small (hb. Haun.), New Jersey (hb. Haun.), 



P. diversifolius Rafinesque, in Medical Repository, 1811, 409. — P. hybridus 

 var. b MicHX, Flora boreali Americana I, 1803, 401, e Raf. 1. c, non hybridus Pet., 

 Inst. bot. 1787. — P. capillaceus Poieet ap. Lamarck, Enc. Suppl. IV, 1816, 535. 

 Fig. 60, M; 61, F. 



T. MoRONG has adopted the Rafinesquian name for this species (Najad., 1893, 

 48). The description, however, may not be considered as fully decisive. It runs: 

 »Potamogeton diversifolium Raf. {P. hybridum b. Mich. fl. bor.) Foliis submersis 



