122 



POTAMOGETONACEAE 



7. Potamogeton cristatus Regel & Maack. P. hybridus 



Makino, non Michx. Koba-no-hieo-mushiro. Similar to 



the preceding, differs in the rather short and densely flowered 

 spikes; nutlets with a short stipe, conspicuously cristate on the 



back; style slender, 1-1.2 mm. long. June-Sept. Ponds; 



Honshu. Ussuri, China, Korea, and Formosa. 



Potamogeton kamogawaensis Miki. O-MizuHiiii-Mo. 

 Kamogawa-mo. An alleged hybrid occurring in Honshu, 

 Shikoku, and Kyushu, very similar to No. 7 and to No. 6, but 

 larger in all respects and becoming slightly darker when dry; 

 submersed leaves 1-2 mm. wide; flowers sterile. 



8. Potamogeton perfoliatus L. Hieoha-no-ebi-mo. 

 Stems elongate, branched, rather densely leafy; floating leaves 

 not developed, the submersed broadly ovate to broadly lanceo- 

 late, 2-6 cm. long, 1-2.5 cm. wide, obtuse to acute, deeply 

 cordate and perfoliate at base, entire and somewhat undulate, 

 3-nerved and with 2 veinlets between the nerves; stipules 

 thinly membranous, soon withering or caducuos; peduncles 

 slightly thickened above; spikes densely flowered, 1.5-2.5 cm. 

 long; nutlets about 3 mm. long, broadly obovate, with an en- 

 tire ridge at the back; style short. June-Sept. Ponds and 



shallow rivers; Hokkaido, Honshu, Shikoku, Kyushu. 



Eurasia, North America, Australia, and Argentina. 



Potamogeton X leptocephalus Koidz. Hieoha-no-sen- 

 NiN-Mo. Hybrid of P. maac\ianus X P. perfoliatus. Leaves 

 narrower than in the parents, 3-3.5 cm. long, 7-8 mm. wide, 



rounded to very obtuse, obscurely serrulate, 5- to 7-nerved. 



Reported from Kyushu. 



9. Potamogeton praelongus Wulfen. Nagaba-ebi-mo. 

 Stems branched; leaves all submersed, narrowly lanceolate, 

 10-20 cm. long, 1-2.5 cm. wide, narrowed toward the obtuse 

 ends, cucullate and recurved at apex, rather many-nerved; 

 stipules whitish, obtuse at apex; peduncles elongate, not 

 thickened above; spikes 3-5 cm. long; nutlets about 4 mm. 



long, the keel entire. Hokkaido. Europe, Siberia, and 



N. America. 



10. Potamogeton dentatus Hagstr. P. teganumensis 



Makino; P. lucens var. teganumensis (Makino) Makino 



Gasha-moku. Stems branched; leaves all submersed, broadly 

 lanceolate or narrowly oblong, 5-15 cm. long, 15-30 mm. wide, 

 mucro at tip 1-4 mm. long, slightly undulate, serrulate toward 

 tip, 7- to 13-nerved, obtuse or acute at base, the petioles 3-12 

 mm. long; stipules 2.5-5 cm. long, obtuse or rounded at 

 apex; peduncles 5-20 cm. long; spikes densely flowered, 3-5 



cm. long; nutlets about 3 mm. long, the keel entire. July- 



Oct. Ponds; Honshu (Kanto and Kinki Distr.). 



11. Potamogeton malaianus Miq. P. japonicus Fr. & 

 Sav.; P. wrightii Morong; P. tretocarpus Maxim.; P. miya}{e- 



jimensis Honda; ? P. gaudichaudii Cham. & Schltdl. Sasa- 



BA-Mo, Sajiba-mo. Stcms simple or slightly branched; 

 leaves all submersed, linear-oblong to lanceolate, 8-12 cm. 

 long, 1-2.5 cm. wide, 7- to 13-nerved, obtuse at base, with a 

 mucro 2-3 mm. long at apex, obscurely serrulate, conspicu- 

 ously undulate on margin, the petioles 1.5-3 cm. long; the 

 stipules 2-4 cm. long; spikes rather densely flowered, 3-5 cm. 

 long; nutlets about 3 mm. long, 3-ridged on back, the median 



ridge more prominent and entire. June-Oct. Ponds and 



shallow rivers; Hokkaido, Honshu, Shikoku, Kyushu. 



Ryukyus, China, Formosa, Malaysia, and India. 



12. Potamogeton crispus L. P. serratus Huds. 



Ebi-mo. Stems slender and branched; submersed leaves lin- 

 ear to broadly so, 4-7 cm. long, 4-6(-8) mm. wide, rounded to 



obtuse at apex, undulate and serrulate, sessile and obtuse or 

 subrounded at base and sometimes slightly clasping, 3-nerved; 

 stipules thinly membranous, about 10 mm. long; peduncles 

 2-5 cm. long; spikes lax and few-flowered, 1-1.5 cm. long; 

 nutlets broadly ovate, about 3 mm. long, obscurely toothed on 

 the median ridge of back; style elongate, about 2 mm. long. 



May-July. Ponds and shallow rivers; Hokkaido, Honshu, 



Shikoku, Kyushu. Worldwide except South America. 



13. Potamogeton compressus L. P. zosteraefolius K. 

 Schum.; P. complanatus Willd.; P. sibiricus auct. Japon., non 



A. Benn. ^Ezo-yanagi-mo. Stems prominendy compressed, 



sometimes 2-winged, much branched; submersed leaves lin- 

 ear, 4-20 cm. long, 2-4 mm. wide, obtuse and mucronate or 

 abrupdy acute, laterally attached on the compressed stem, 

 entire, 3-nerved and with veinlets between the nerves; stipules 

 2-4 cm. long, withering or caducous; peduncles 2-4 cm. long; 

 spikes about 15 mm. long; nutlets broadly obovate, 2-3 mm. 



long, keeled. Reported from Hokkaido. Eurasia and N. 



America. 



14. Potamogeton oxyphyUus Miq. Yanagi-mo. Stems 

 slender and branched; leaves all submersed, Unear, 5-10(-12) 

 cm. long, 2-3 mm. wide, acuminate, entire, sessile, with very 

 faint nerves on both sides, the stipules about 2 cm. long, obtuse, 

 thinly membranous and their margins overlapping; peduncles 

 2-4 cm. long; spikes rather densely flowered, 1-1.5 cm. 

 long; nutlets broadly elhptic-ovate, about 3.5 mm. long, sub- 

 entire; style short. ^May-Oct. Ponds and shallow rivers; 



Hokkaido, Honshu, Shikoku, Kyushu. ^Korea and Man- 

 churia. 



Potamogeton X fauriei (A. Benn.) Miki. P. oxyphyllus 



var. fauriei A. Benn. Ainoko-yanagi-mo. An alleged 



hybrid of No. 14 and No. 13. A coarser plant with leaves 17- 

 to 19-nerved; spikes loosely flowered and sterile. 



15. Potamogeton berchtoldii Fieber. P. pusillus auct., 

 non L. Ito-mo. Stems very slender and scarcely com- 

 pressed; leaves all submersed, linear, dark green, 3-5 cm. long, 

 1-1.5 mm. wide, acute to subobtuse, 1- to 3-nerved or some- 

 times nerveless, with a somewhat reflexed gland on each side 

 at base; stipules about 10 mm. long, margins overlapping; 

 peduncles 2-4 cm. long; spikes rather few-flowered; nutlets 

 broadly elliptic-ovate, about 1.5 mm. long, with 3 low ridges 



on back. ^May-Aug. Ponds and shallow rivers; Hokkaido, 



Honshu, Shikoku, Kyushu. Widely distributed in the N. 



Hemisphere. 



16. Potamogeton pusillus L. P. panormitanus Biv. 



TsuTsu-iTo-MO. Very similar to the preceding; leaves vivid 



green; stipules tubular with an obliquely truncate mouth. 



Reported from Honshu, Shikoku. Widely distributed in the 



N. Hemisphere, inclusive of the West Indies and Azores. 



17. Potamogeton maackianus A. Benn. P. serrulatus 

 Regel & Maack, non Schrad. nee Opiz; P. robbinsii var. ja- 

 ponicus A. Benn.; P. tenuif alius A. Camus Sennin-mo. 



Stems slender and much branched; leaves all submersed, lin- 

 ear, 2-6 cm. long, 2-3 mm. wide, finely serrulate, 3-nerved 

 and faindy nervulate, becoming broadly obtuse to rounded at 

 apex, briefly adnate to the stipules at base; stipules about 10 

 mm. long, membranous; peduncles 1-3 cm. long; spikes few- 

 flowered; nutlets broadly ovate-elliptic, about 3 mm. long, 



with an acute keel; style short. ^May-Sept. Ponds and 



shallow rivers; Hokkaido, Honshu, Kyushu. e. Siberia, 



Korea, and Manchuria. 



18. Potamogeton pectinatus L. Ryu-no-hige-mo. 



