128 Hydrocharitaceae 



Fam. 39. HYDROCHARITACEAE Tochi-kagami Ka Frogbit Family 



Fresh- or salt-water herbs; flowers on scapes or sometimes on leafy stems; leaves linear to rounded, sometimes opposite or 

 verticillate; flowers solitary or subumbellate, unisexual or bisexual, at first enclosed in 1 or 2 sheathed bracts; outer perianth- 

 segments 3, thin, the inner 3, or sometimes 2, petallike, or absent; stamens 3, 6, 9, 12, or rarely many, the anthers 2-locular, 

 longitudinally dehiscent; ovary inferior, 1-locular or incompletely many-locular, the placentae parietal; styles often connate, the 



stigmas entire or bifid; ovules many, anatropous; seeds numerous, oblong, endosperm absent. About 15 genera, with about 



100 species in tropical and temperate regions. 



lA. Marine herbs with creeping stems; leaves opposite, petiolate, ovate to oblong, penninerved; flowers solitary, unisexual, the inner 



perianth-segments absent; stamens 3; ovary 1-locular; styles 3 1. Halophila 



IB. Fresh water herbs. 

 2A. Ovary 1-locular, with scarcely protruded, parietal placentae; leaves narrow. 

 3A. Leaves radical or alternate. 



4A. Flowers usually bisexual, sometimes unisexual, the spathe cylindric, staminate flowers not detached from the pedicels nor 



floating at anthesis; inner perianth-segments present; stamens 3—9 2. Blyxa 



4B. Flowers unisexual (plants usually dioecious), with an ovoid spathe in the staminate, cylindric in the pistillate; staminate flowers 



detached from the pedicels before anthesis and floating; inner perianth-segments absent; stamens 1—3 3. Vallisneria 



3B. Leaves verticillate; staminate flowers solitary, enclosed in a spathe; inner perianth-segments present; stamens 3 4. Hydrilla 



2B. Ovary 6- to 15-locular, with protruding placentae; leaves broad. 



5A. Flowers bisexual; leaves immersed 5. Ottelia 



5B. Flowers unisexual; leaves floating 6. Hydrocharis 



1. HALOPHILA Thou. Umi-hiru-mo Zoku 



Immersed marine monoecious or dioecious herbs with long-creeping stems; leaves from the axils of hyaline scales, binate, 

 petiolate, ovate or narrowly oblong, pinnately veined; spathe small, sessile, solitary among the binate leaves, consisting of 2 

 bracts enclosing a single flower; flowers unisexual, the staminate pedicelled, the outer perianth-segments 3, the inner absent; 

 stamens 3, alternate with the outer perianth-segments, the anthers subsessile and extrorse; pistillate flowers sessile, with 3 minute 

 outer perianth-segments, the ovary long-beaked, 1-locular, the styles 3, filiform, papillose; ovules in 2 series, on 2 parietal placen- 

 tae; fruit subglobose, beaked; seeds numerous, globose, each with a coiled cotyledon. ^Few species in tropical regions of the 



Pacific basin. 



1. Halophila ovalis (R. Br.) Hook. f. CauUnia ovalis with 3 principal veins and 10-20 pairs of connecting veinlets, 



R. Br.; H. ovata Gaudich.; Bar\ama punctata Ehrenb.; H. the petioles purplish, with a hyaline membranous scale at base; 



euphlebia Makino Umi-hiru-mo, O-umi-hiru-mo. Per- pistillate flowers axillary, sessile, 2-bracteate. On sandy sea 



ennial herb; stems creeping, sparingly branched, rooted at the bottoms; Honshu (Sagami, Noto and westw.), Shikoku, Kyu- 



nodes; leaves petiolate, narrowly oblong to elliptic-ovate, 15-25 shu. India, Malaysia, and Australia. 



mm. long, 6-15 mm. wide, entire, rounded at apex, smooth, 



2. BLYXA Thou. SubutaZoku 



Aquatic annuals; stems rarely elongate; leaves radical or alternate, linear, sessile, acute to acuminate; staminate flowers several 

 within a cylindrical spathe, the outer perianth-segments 3, linear, the inner 3 longer than the outer, linear, the stamens 3-9, 

 sometimes partly reduced, with 3 reduced pistils; pistillate flowers solitary within a spathe, sessile, the perianth similar to the 

 staminate, the stamens rudimentary or absent, the ovary cylindrical, beaked, 1-locular, the style short, the stigmas elongate; 



fruit cylindric, inclosed in a spathe, the seeds numerous, minute, oblong. ^More than 10 species in tropical and subtropical 



regions of Asia and Africa. 



lA. Stems distinctly elongate, sometimes branched; peduncles absent; leaves 3-5 cm. long, 2—3 mm. wide; fruit about 2 cm. long, 



enclosed in a short spathe; seeds smooth, without tails 1. B. japonica 



IB. Stems absent or nearly so; peduncles present; leaves 5-30 cm. long, 4-8 mm. wide; fruit 2-5 cm. long. 

 2A. Seeds without a taillike appendage at both ends. 



3A. Seeds smooth 2. B. leiosperma 



3B. Seeds sparsely tuberculate 3. B. aubertii 



2B. Seeds with a taillike appendage at both ends. 



4A. Taillike appendages shorter than or as long as the seed 4. B. ceratosperma 



4B. Taillike appendages much longer than the seed 5. B. bicaudata 



1. Blyxa japonica (Miq.) Maxim. ? Hydrilla japon- 3, lanceolate, obtuse, about 3 mm. long; petals linear, twice as 



ica Miq.; B. caulescens Maxim.; B. leiocarpa Maxim. long as the sepals; stamens 3; fruit linear-cylindric, 1.5-2 cm. 



Yanagi-sobuta. Stems 5-20 cm. long, simple or sparmgly long; seeds lanceolate, smooth, obtuse at both ends, 2 mm. 



branched, densely leafy; leaves linear, flat, gradually nar- long, 0.5 mm. wide. Aug.-Oct. Common in paddy fields; 



rowed to the tip, minutely serrulate; flowers bisexual, solitary, Honshu, Shikoku, Kyushu. Korea and Formosa. 



sessile, the cylindrical spathe 15-20 mm. long, sessile; sepals 2, Blyxa leiosperma Koidz. Mikawa-subuta. An- 



