Potamogetonaceae; Najadaceae 123 



Stems filiform, yellowish, much branched; leaves all sub- spikes remotely few-flowered, 2-4 cm. long; nutlets broadly 



mersed, filiform, 3-10 cm. long, 0.5-1 mm. wide, entire and obovate, 3-3.5 mm. long, usually rounded and entire on back. 



acute at apex; stipules 1-2 cm. long, whitish, membranous, June-Oct. Ponds and shallow rivers, especially near sea- 



adnate to the base of the leaves from three-fourths to six- shores; Hokkaido, Honshu, Shikoku, Kyushu. Eurasia, N. 



sevenths of their length; peduncles slender, 2-10 cm. long; America, Africa, and Australia. 



2. RUPPIA L. Kawa-tsuru-mo ZoKU 



Much branched delicate aquatic herbs with filiform branches; leaves alternate, narrow, l-nerved, subtended by a mem- 

 branous sheath; peduncles solitary, axillary, elongate after flowering; flowers without a perianth; stamens 2; anthers attached 

 to the peduncle at die back, with 2 distinct anther-locules; stigma sessile and peltate; nudets small, long-pedicelled, obliquely 

 ovate. Four or five widely distributed species. 



1. Ruppia rostellata Koch. R. maritima L., pro parte; Shikoku, Kyushu. Eurasia, Africa, and N. America. 



R. maritima var. rostrata Agardh Kawa-tsuru-mo. Deli- Ruppia maritima L. R. spiralis L.; R. maritima var. spi- 



cate aquatic herb; stems much branched, elongate; leaves ralis Mori Nejiri-kawa-tsuru-mo of Eurasia, N. America. 



filiform, slighdy compressed in cross section, 0.3-0.5 mm. wide, and Africa, with spirally coiled, elongate peduncles in fruit, is 



5-10 cm. long, acuminate, remotely serrulate toward die tip; reported from Japan and figured by Miki, in Yamashiro Suiso- 



sheath 8-15 mm. long, with a rounded mouth; nudets 2-4, shi, /zg-. 29. 1937. 



obliquely ovate, biconvex, about 2.5 mm. long, short-beaked, Ruppia truncatifolia Miki. Known only in the sterile 

 on a slighdy curved peduncle 1.5^ cm. long. June-Oct. state; leaves 0.3-0.7 mm. wide, truncate-retuse at apex. Re- 

 Ponds and shallow rivers; Honshu (Kanto Distr. and westw.), ported from Hokkaido and Korea. 



3. ZANNICHELLIA L. Ito-kuzu-mo Zoku 



Aquatic monoecious herbs, with slender creeping rhizomes; stems delicate, elongate; leaves submersed, narrowly linear, 

 stipulate; flowers axillary, the staminate solitary and sessile, consisting of only 1 stamen with a 2-locular anther, the pistillate 

 consisting of 2-5 free, sessile or stipitate carpels; stigma peltate; nudets lunate, usually with obtuse teeth at back, the embryo 

 coiled. Two or three widely distributed species. 



1. Zannichellia palustris L. var. indica (Cham.) long; nudets 2-5, stipitate, about 3 mm. long, lunate, nar- 



Graebn. Z. indica Cham.; Z. palustris var. japonica Makino rowly oblong, remotely cristate-dentate on back, the stipe 



Ito-kuzu-mo, Mikazuki-ito-mo. Stems slender; leaves 1.5-3.3 mm. long; style 2.5-3 mm. long, slender. Honshu, 



less than 1 mm. wide, narrowly linear; peduncles 1-2.5 mm. Kyushu. Ryukyus and India. The species is cosmopolitan. 



Fam. 35. NAJADACEAE Ibara-mo Ka Naiad Family 



Submersed dioecious or monoecious aquatic herbs growing in fresh or saline waters; stems much branched; leaves opposite, 

 or verticillate, linear, spiny-margined, sheathed at base; flowers solitary in the leaf-axils, the staminate pedicellate, the perianth 

 hyaline, bifid at apex; stamen 1, the anther 1- to 4-locular, pistillate flowers terminated by 2-4 linear stigmas; fruit achenelike, 

 1-seeded, the embryo straight. With a single genus of wide distribution, nearly cosmopolitan. 



1. NAJAS L. Ibara-mo Zoku 



Characters of the family. About 10 species widely distributed. 



lA. Margin of leaf-sheath entire; leaves 1-3 mm. wide, remotely serrate, the teeth spinescent; flowers dioecious; seeds ellipsoidal to ob- 

 long, 1.5-2.5 mm. wide. 



2A. Leaves 2-3 mm. wide, with 9-11 teeth on each side 1- N. manna 



2B. Leaves about 1 mm. wide, with 2-4 teeth on each side 2. N. tenuicauUs 



IB. Margin of leaf-sheath denticulate; leaves usually narrow, less than 1 mm. wide, finely toothed; flowers monoecious; seeds lanceolate, 

 less than I mm. wide. 



3A. Seeds prominently curved; pistillate flowers with a bracteate sheath 3. N. ancistrocarpa 



3B. Seeds straight; pistillate flowers without a bracteate sheath. 



4A. Staminate flowers bracteate; Icaf-sheath not distinctly extended, obliquely rounded at apex. 

 5A. Leaves scarcely compressed; seeds with oblong to linear superficial cells. 

 6A. Superficial cells of seeds transversely elongate. 



7A. Leaves about 3 cm. long, 0.8 mm. wide; seeds 3.5-4 mm. long 4. JV. ogiiracnsis 



7B. l.eaves 1.5-2 cm. long, 0.3-0.5 mm. wide; seeds 3 mm. long 5. N. minor 



6B. Superficial cells of seeds longitudinally elongate. 



8A. Superficial cells of seeds narrowly oblong; seeds 2.5-3 mm. long, oblong 6. N. yezocnsis 



8B. Superficial cells of seeds linear; seeds about 2 mm. long, lanceolate 7. N. japonica 



5B. Leaves flat; seeds with hexagonal superficial cells 8. N. indica 



4B. Staminate flowers without a bracteate sheath; leaf sheath auriculate at apex 9. N. graminea 



