138 j. o. hågström, critical researches on the potamogetons. 



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



Caulis teres— subteres 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 inferiorum foliorum 

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

 angustissime linearia subobtusa vaginata ligulata 50 — 70 X 0,75 mm; ramalina breviora, 

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

 fimae ca. 8-florse, summas ca. 20-florae. Fruetus parvus, 1,8 x 1 mm, rotundatus, a 

 latere compressus, erostratus tricarinatus carinis gibbosis. — 



This species has qualities reminding both of P. dimorphus and of diversijolius. 

 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- 

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

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

 just mentioned species, but seldom (the uppermost) or ne ver they terminate them- 

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

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

 t han that of P. diversijolius, 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, C! The upper spikes are many-flowered; all richly fruiting, consequently it 

 should not be considered a hybrid in usual sense, though probably of a h) T biid origin. 



The species has been mixed up with P. diversijolius, 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 see ms always to be present in the stem. 



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

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



I*. (livcrsifolius Rafinesque, in Medical Repository, 1811, 409. - P. hybridus 

 rar. b Miciix, Flora boreali Americana 1, 1S03, 401, e Raf. 1. c, non hybridus Pet., 

 lust. bot. 1787. — /'. aipillaeeus PoiBET ap. LåMåBOE, Ene. Suppl. IV, 1816,53;"». 

 Fig. 60, .1/,- 61, /'. 



T. Moeonq has adopted (lic Rafinesquian aame for this species (Najad., 189$, 



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



1'nloniogelon (lirrrsifoliuni Raf. (/'. hybridum b. Micn. fl. bor.) Poliis Btibmefsis 



