120 Sparganiaceae; Potamogetonaceae 



wide, not keeled, with a slightly dilated sheath at base; spikes erect, as long as or slightly longer than the spikes, 4-10 mm. 



aerial, 10-15 cm. long, with 1 or 2 branches; staminate heads wide; spikes simple, more or less distant, the bracts usually 



few, contiguous; pistillate heads 1-3 on each branch, globose, longer than the spike; pistillate heads 3 or 4, 1.5-2 cm. in 



7-8 mm. across in fruit, the lower ones peduncled and pro- diameter in fruit, the lower 1 or 2 heads usually peduncled, 



vided with a leafy bract; flowers with linear-spathulate perianth the staminate 5-10; fruit oblong-fusiform, about 5 mm. long, 



segments about 1.5 mm. long; fruit broadly ovoid, conical, 1.5-2 mm. across, not angled, with a slight constriction in tlie 



subsessile, not angled, about 3 mm. long, 2 mm. in diameter; middle, narrowed toward both ends, the pedicels about 2 mm. 



stigma ovate-peltate. July-Aug. Ponds in high mountains; long; style including the linear stigma, about 2 mm. long. 



rare. Hondo (Echigo). Europe, Siberia, and Kamchatka. July-Aug. Shallow water in lowlands; Honshu, Kyushu. 



7. Sparganium stenophyllum Maxim. 5. nipponicum Korea. 



Makino ^Hime-mikuei. Stems erect, usually rather slen- 9. Sparganium hyperboreum Laest. S. natans var. 



der, 40-70 cm. long; leaves keeled beneath, suberect, usually submuticum Hartm.; S. submuticum (Hartm.) Neumann; S. 



somewhat longer than the stem, 3-5 mm. wide; spikes simple minimum sensu auct. Japon., non Fries Chishima-mikuri, 



or with a single branch at base, the bracts nearly as long as Takane-mikuri. Stems elongate, submersed; leaves slender, 



the spike; pistillate heads 2 or 3 (-4), sessile, axillary, distant compressed, not keeled, 2-4 mm. wide, obtuse; spikes simple, 



in fruit, about 1.5 cm. in diameter, the staminate few, distant; commonly 2-3 cm. long, the bracts longer than the spikes; 



fruit obovoid, subsessile, about 4 mm. long, abruptly narrowed pistillate heads 2 or 3, 6-8 mm. in diameter in fruit, the lowest 



to the style. June-Sept. Shallow water in lowlands; Hok- one usually with a supra-axillary peduncle, the staminate heads 



kaido, Honshu, Kyushu. n. China and Ussuri. 1 or 2, close together and closely adjacent to the pistillate 



8. Sparganium japonicum Rothert. Nagae-mikuri. heads; fruit ovoid, with a narrowly ovate stigma. ^Ponds; 



Stems erect, 40-70 cm. long; leaves flat, keeled beneath, sub- Hokkaido (Mount Taisetsu) . Subarctic regions. 



Fam. 34. POTAMOGETONACEAE Hiru-mushiro Ka Pondweed Family 



Aquatic herbs growing in fresh or rarely in saline water, mostly submerged but also with floating leaves; leaves sessile or 

 petioled, filiform or flattened, usually entire; flowers perfect or monoecious, without a perianth; inflorescence spicate or 

 fasciculate, axillary, sometimes enveloped by a scarious sheath; stamens 1-4, the anthers extrorse, 1- to 2-locular, the connective 

 sometimes (Potamogeton) bearing sepallike appendages; pistil of 1-4 separate 1-ovulate carpels each developing into a nutlet 

 or drupelike fruit; endosperm absent. ^About 4 genera with more than 100 species, of wide distribution. 



lA. Flowers perfect; stamens 2 or 4. 



2A. Stamens 4; fruit sessile; peduncles straight or slightly curved; connective with a sepallike appendage 1. Potamogeton 



2B. Stamens 2; fruit long-pedicelled; peduncles spirally curved after flowering; connective without a perianthlike appendage. . . 2. Ruppia 



IB. Flowers monoecious; stamen 1 3. Zannichellia 



1. POTAMOGETON L. Hiru-mushiro Zoku 



Aquatic herbs, attached to the bottom by roots and rhizomes; stems elongate, sometimes branched; leaves often dimorphic, 

 alternate, those of the inflorescence sometimes approximate, the submerged leaves usually linear, the floating lanceolate to elliptic, 

 the stipules membranous, free or adnate to the basal portion of the blade or to the petiole, sometimes connate to form a 

 tubular sheath; peduncles axillary; flowers small, in axillary spikes, perianth wanting; stamens 4, the anthers sessile, the con- 

 nective dilated at tip into a perianthlike appendage, the anther-locules distinct or connate; ovary of (1-) 4 distinct, sessile, 



1-locular and 1-ovuled carpels; stigma simple; nutlets 1-4, 1-seeded, the seeds filling the nutlet, the embryo curved. About 



100 species, in temperate regions of the world. 



lA. Plants with floating leaves. 

 2A. Floating leaves 5-12 cm. long, 2.5-5 cm. wide. 



3A. Submersed leaves semiterete, slenderly linear \. P. natans 



3B. Submersed leaves with lanceolate blades. 



4A. Submersed leaves petiolate 3. P. distincttis 



4B. Submersed leaves sessile, the floating leaves sometimes not developed. 



5A. Petioles of the floating leaves with margin undulate near top 2. P. jryeri 



5B. Petioles of the floating leaves without undulate margin. 



6A. Floating leaves narrowly ovate to broadly-lanceolate; stems branched; winter buds with several nodes; peduncles thick- 

 ened above; submersed leaves 3-5 cm. long 4. P. heterophyllus 



6B. Floating leaves spathulate; stems usually not branched; winter buds with 1 node; peduncles hardly thickened above; 



submersed leaves 8-20 cm. long 5. P. alphas 



2B. Floating leaves 1.5-3.5 cm. long, 5-12 mm. wide; submersed leaves all linear. 



7A. Nutlets entire or obtusely dentate on the dorsal margin; style short 6. P. octandrus 



7B. Nutlets conspicuously cristate on the dorsal margin; style long and slender 7. P. cristattis 



IB. Plants without floating leaves; leaves all submersed. 

 8A. Leaves not adnate to the stipules at base. 



9A. Leaves 7-30 mm. wide, lanceolate or narrowly so. 



1 A. Leaves sessile or nearly so, obtuse or acute, not mucronate. 



1 1 A. Leaves perfoliate 8. P. perfoUatus 



