Hydrocharitaceae 



129 



nual; stems absent or nearly so; leaves radical, rosulate, linear, 

 7-15 cm. long, 4-5 mm. wide, acuminate, minutely serrulate; 

 peduncles axillary, 1-3 cm. long, terminated by a cylindrical 

 spathe about 3.5 cm. long; flowers solitary within the spathe, 

 sessile; sepals 3, linear, 6-10 mm. long, obtuse; petals 3, nar- 

 rowly linear, about 14 mm. long; seeds numerous, oblong, 



smooth, obtuse at both ends. Oct. Honshu; rare. 



3. BIyxa aubertii Rich. B. coreana Nakai (excl. basi- 

 onym ? HydroUrion coreanum Lev.); B. ecaudata Hayata; B. 



muricata Koidz. Marumi-sueuta, 0-subuta. Stemless 



annual; leaves rosulate, linear, 7-20 cm. long, 4-7 mm. wide, 

 gradually acuminate, minutely serrulate, more or less 5-veined 

 with a number of cross veinlets; peduncles 5-7 cm. long, the 

 spathe cylindrical, 4-5 cm. long, slighdy longer than the fruit; 



sepals 3, lanceolate, obtuse; fruit linear; seeds ellipsoidal, about 

 1.5 mm. long, 0.8 mm. wide, obscurely striate with scattered 

 tubercles. Shallow ponds and paddy fields; Honshu, Kyu- 

 shu. Korea, Formosa, China, India, and Australia. 



4. Blyxa ceratosperma Maxim. Nacaba-subuta, Su- 

 BUTA. Very similar to the preceding but the seeds provided 

 with a taillike appendage at each end, these nearly as long as 



or shorter than the seed. Aug.-Oct. Shallow ponds and 



paddy fields; Honshu, Kyushu; common. Formosa. 



5. Blyxa bicaudata Nakai. B. shimadae sensu Miki, non 

 Hayata (?). Ko-subuta, Naga-hige-mi-subuta. Very simi- 

 lar to No. 3 and No. 4, but the seeds with the taillike ap- 

 pendages 2-4 times as long as the seed. Honshu; rare. 



3. VALLISNERIA L. Sekisho-mo Zoku 



Stemless, usually stoloniferous dioecious herbs wholly immersed; leaves rosulate, ribbonlike, compressed, serrulate at least in 

 upper part, short-sheathed at base; peduncles radical, with a terminal spathe; flowers apetalous, the staminate small, numerous 

 in a short peduncled ovoid spathe, each detached from the peduncle and floating freely before anthesis, die outer perianth- 

 segments 3, the stamens 1-3; pistillate flowers solitary in a cylindrical spathe on a long peduncle, coiling after the flower is 

 pollinated on the surface; ovary linear, inferior, 1-locuIar, with 3 parietal placentas; stigmas 3, alternate with the outer perianth- 

 segments; fruit linear, with numerous fusiform seeds. Few species in tropical and subtropical regions, except S. America. 



lA. Winter buds fusiform; leaves prominently serrulate, abruptly acute; stolons rough with small spiny protuberances; stamens 2; seeds 



1.5 mm. long \.V. denseserrtihta 



IB. Winter buds absent; leaves slightly serrulate; stolons smooth; stamen 1. 



2A. Ovary minutely tubercled; leaves 6-13 mm. wide, 5- to 7-veined, rather obtuse, slightly serrulate only toward tip; seeds 3.5 mm. 



long 3. V. higoensis 



2B. Ovary smooth; leaves 5-10 mm. wide, 3- to 5-veLned; seeds 3 mm. long. 



3A. Ovary tightly enclosed in the spathe; leaves scarcely twisted, slightly serrulate only toward tip, acute at apex 2. V. asiatica 



3B. Ovary loosely enclosed in the spathe; leaves much twisted, serrulate on margin, obtuse to abruptly acute at apex. . . 4. F. biwaensis 



1. Vallisneria densesemilata (Makino) Makino. V. 



spiralis var. denseserrulata Makino K6gai-mo. Perennial 



with roughened stolons; leaves linear, 4-10 mm. wide, abruptly 

 acute, flattened, elongate, densely and prominently serrulate, 

 5-veined; spathe about 1.3 cm. long, loosely enveloping the 

 ovary at anthesis; ovary smooth, linear, about 12 cm. long in 



fruit; seeds narrowly obovoid, 1.5 mm. long. ^Aug.-Oct. 



Shallow rivers and ponds; Honshu. 



2. Vallisneria asiatica Miki. V. spiralis sensu auct. Ja- 

 pon., non L.; V . spiralis var. subulispatha Makino, including 



forma minor Makino; V. subulispatha (Makino) Koidz. 



Sekisho-mo. Perennial with smooth stolons; leaves elongate, 

 linear, flattened, 5-7 mm. wide, 5-veined, loosely and obscurely 

 serrulate toward tip; pistillate flowers enveloped by a spathe 

 about 2 cm. long; staminate peduncles 2-3 cm. long; fruit 

 linear, smooth, 15-20 cm. long; seeds narrowly fusiform, 3 



mm. long. Aug.-Oct. Ponds and shallow rivers; Hok- 

 kaido, Honshu, Shikoku, Kyushu; common. China, Indo- 

 china, Korea, and Formosa. 



3. Vallisneria higoensis (Miki) Ohwi. V. asiatica var. 



higoensis Miki Hira-mo, Hiroha-sekish6-mo. Similar to 



the preceding; leaves 6-13 mm. wide, 5- to 7-veined, obtuse 

 to abrupdy acute; ovary tubercled; fruit about 10 cm. long, 



5 mm. wide; seeds about 3.5 mm. long, 0.8 mm. wide. 



Kyushu; rare. 



4. Vallisneria biwaensis (Miki) Ohwi. V. asiatica var. 



biwaensis Miki Nejire-mo. Similar to No. 2, but the 



leaves prominendy twisted, 5-10 mm. wide, 5-veined, obtuse 

 to abrupdy acute, serrulate throughout; pistillate spathe about 

 15 mm. long, loosely enveloping the ovary, the staminate 



peduncles 3-5 cm. long. Aug.-Oct. Shallow rivers and 



ponds; Honshu (Kinki Distr.). 



4. HYDRILLA L. C. Rich. Kuro-mo Zoku 



Dioecious aquatic herbs with elongate stems; leaves verticillate, sometimes opposite, rather short; staminate flowers solitary, 

 axillary, short-peduncled, enveloped by a globose spathe, detached from the spathe and freely floating above the water at 

 anthesis, the perianth-segments 6, in 2 rows, the stamens 3; pistillate flowers enveloped by a cylindrical spathe, sessile, the 

 ovary inferior, I-locular, beaked, the stigmas' 3j fruit linear, smooth or tubercled; seeds 1-3, fusiform with slightly elongate 

 ends. Two species widely distributed' in tropical and temperate regions of the Old World. 



1. Hydrilla verticillata (L. f.) Casp. Serpicula verti- 1-3, acute at both ends, 5-6 mm. long, short<ylindrical. 



cillata L. f. Kuro-mo. Stems elongate, loosely branch- Aug.-Oct. Ponds; Hokkaido (rare), Honshu, Shikoku, Kyu- 



ing; leaves verticillate in 4's to 8's, narrowly lanceolate, spread- shu; common. Eurasia, Malaysia, Australia, and Madagas- 



ing, 1-nerved, 1-2 cm. long, 1.5-2 mm. wide, serrate, acuminate car. 

 and ending in a minute spine; pistillate flowers axillary; seeds 



