POTAMOGETONACEAE 



121 



IIB. Leaves narrowed at base, not perfoliate. 

 12A. Leaves flattened at apex. 



13 A. Stems branched; winter buds with several nodes; submersed leaves 4-8 cm. long 4. P. heterophylliis 



13B. Stems usually not branched; winter buds with 1 node; submersed leaves 8-20 cm. long 5. P. alpinus 



12B. Leaves cucullate at apex 9. P. pradongiis 



lOB. Leaves more or less petiolate, abruptly acuminate or taper-pointed. 



14A. Petioles 3-12 mm. long 10. P. dentatus 



14B. Petioles 1.5-3 cm. long 1 1. P. malaianus 



9B. Leaves 1-6 mm. wide, linear. 



15A. Leaves serrulate, 4-6 mm. wide, sometimes clasping at base 12. P. crisptis 



15B. Leaves entire, 1-3 mm. wide. 



16A. Margins of the stipules free, overlapping. 



17A. Stems distinctly compressed, thicker than the peduncles 13. P. comprcssiis 



17B. Stems only slightly compressed, as thick as the peduncles. 



18A. Leaves 2-3 mm. wide, acuminate; nutlets 3 mm. long; rhizomes slender. . . .• 14. P. oxyphyllus 



18B. Leaves 1-1.5 mm. wide, acute; nutlets about 1.7 mm. long; rhizomes absent 15. P. berchtoldii 



16B. Margins of the stipules united into a tubular sheath 16. P. pusilliis 



B. Leaves adnate to the stipules at base. 



19A. Leaves 2-3 mm. wide, serrate, with a broad obtuse projection at apex 17. P. maackianus 



19B. Leaves about 1 mm. wide, entire, acute 1 8. P. pectinattis 



1. Potamogeton natans L. P. morongii A. Benn. 



0-HiRU-MUSHiRO, Me-hiru-mushiro. Stcms often elongate; 

 floating leaves thickish, long-petiolate, ovate-oblong to elliptic, 

 5-10 cm. long, 2.5 — 5 cm. wide, many-nerved, entire, apiculate, 

 rounded at base, the submersed leaves semiterete, slenderly 

 linear, the stipules 5-8 cm. long, membranous and many- 

 nerved; peduncles 5-10 cm. long, as thick as the stem through- 

 out, bearing densely flowered spikes 4-6 cm. long; nudets 

 broadly ovate, 3.5-4 mm. long, nearly entire on dorsal ridge. 

 Apr.-Aug. Ponds and shallow rivers; Hokkaido, Hon- 

 shu, Shikoku, Kyushu. Widely distributed in temperate 



regions. 



2. Potamogeton fryeri A. Benn. P. subsessilijoKus A. 

 Camus; P. torquatus Koidz. Futo-hiru-mushiro. Simi- 

 lar to the preceding, but the submersed leaves with blades 

 linear-lanceolate, elongate, the floating leaves long-petiolate, 

 oblanceolate to elliptic, 10-15 cm. long, rounded and decurrent 

 at base, the stipules 5-10 cm. long; peduncles 10-15 cm. long, 

 thickened above, bearing densely flowered spikes; nudets 4, 

 about 5 mm. long, narrowly winged on dorsal ridge. Apr.- 

 Aug. Ponds; Hokkaido, Honshu, Kyushu. Korea. 



3. Potamogeton distinctus A. Benn. P. longipetiolattis 

 A. Camus; P. alatus Koidz.; P. tepperi auct. Japon., non A. 

 Benn.; P. jranchetii A. Benn.; P. polygonijoUus auct. Japon., 



non Pourr. Hiru-mushiro. Stems elongate; floating 



leaves broadly lanceolate to ovate-elliptic, 5-10 cm. long, 

 (1.5-)2-4 cm. wide, petioles 6-10 cm. long, the submersed 

 leaves lanceolate, long-petiolate, acute at both ends, minutely 

 serrulate with projecting marginal cells; stipules 3-4.5 cm. 

 long, thinly membranous, soon decaying; peduncles not 

 thickened above; spikes 2-5 cm. long; nuriets 3-3.5 mm. long, 



ridged on the dorsal margin, the style short. June-Sept. 



Ponds and paddy fields; Hokkaido, Honshu, Shikoku, Kyushu. 

 Korea and China. 



Potamogeton X malainoides Miki. Ainoko-hiru-mu- 

 SHiRo. Hybrid of P. distinctus X P. malaianus. Submersed 



leaves similar to those of No. II. Reported from Honshu 



(Kinki Distr.), Shikoku. Formosa. 



4. Potamogeton heterophyllus Schreb. P. gramineus 

 var. heterophyllus (Schreb.) Fries; P. heterophyllus var. jolio- 



sus Mert. & Koch; P. gramineus auct., non L. Ezo-no-hiru- 



MusHiRo. Stems elongate and often branched; floating 



leaves entire, long-petiolate, rather abruptiy obtuse, rounded 



at the base, 2.5-10 cm. long, 1-3 cm. wide, the submersed 

 leaves sessile, thin, oblanceolate, 4-8 cm. long, 6-10 mm. wide, 

 acute, entire; stipules thinly membranous; peduncles thickened 



above; spikes 2-4 cm. long. July-Sept. Ponds; Hokkaido, 



Honshu (centr. mts.). Temperate regions of the N. Hemis- 

 phere. 



Potamogeton nipponicus Makino. Sasa-ebi-mo. Al- 

 leged hybrid similar to No. 4; stems not flexuose, very rarely 

 with floating leaves and with slightly serrate, submersed leaves, 



the upper ones very short-petiolate. Reported from Honshu 



(Nikko and Hakone). 



5. Potamogeton alpinus Balbis. P. rufescens Schrad. 



HosoBA-HiRU-MusHiRO. Stems simple or slightly 



branched; floating leaves spathulate or oblanceolate, sometimes 

 not developed, obtuse, gradually narrowed to the base, many- 

 nerved, the lower submersed leaves sessile, the upper short- 

 petiolate, narrowly lanceolate, narrowed toward the base, 

 7-nerved, obtuse to acute; peduncles 5-20 cm. long; spikes 

 2.5^ cm. long; nutlets obovate, with 3 dorsal ridges; style 



short. Reported from Hokkaido. Cooler regions of the 



N. Hemisphere. 



6. Potamogeton octandrus Poir. P. javanicus Hassk.; 



P. nuTnasa\ianus A. Benn. Hosoba-mizuhiki-mo. Plant 



small, slender, with filiform sometimes branched stems; float- 

 ing leaves broad-lanceolate to ovate-oblong, 1.5-2.5 cm. long, 

 3-8 mm. wide, acute or abruptiy obtuse, rather acute at base, 

 7-nerved, entire, the petioles shorter than the blades, sub- 

 mersed leaves filiform, 3-6 cm. long, 0.3-1 mm. wide, very 

 acute; stipules thinly membranous, 6-10 mm. long, their edges 

 overlapping; peduncles 1-2 cm. long, slightly thickened above; 

 spikes 1-1.5 cm. long, more or less dense; nutlets sessile, 

 broadly obovate, about 2 mm. long, 3-ridged on the back, the 

 median ridge acute, with a few obtuse teeth; style rather short. 



June-Oct. Ponds and paddy fields; Hokkaido, Honshu, 



Shikoku, Kyushu. Korea, China, Ussuri, Formosa, India, 



and Malaysia. 



Var. miduhikimo (Makino) Hara. P. miduhi/(imo Ma- 

 kino; P. asiaticus A. Benn.; ? P. limosellijoUus Maxim.; ? P. 



subjuscus A. Benn.; P. vascyi Miki, non Robins. Mizu- 



HiKi-Mo. Leaves broadly lanceolate to narrowly ovate-ellip- 

 tic; median ridge of the nutiet destitute of teeth; style short. 



June-Oct. Ponds and paddy fields; Honshu, Shikoku, 



Kyushu. 



