Monochoria vaginalis (Burm. f.) C. Presl.
monochoria, oval-leaf monochoria, pickerelweed
Fruit a capsule with numerous seeds. Seeds terete, elliptic to slightly ovate or occasionally oblong in outline, 0.6–1.2 mm long, 0.4–0.6 mm in diameter, with 8–12 longitudinal low ridges evenly spaced around seed; raphe sometimes present as a prominent longitudinal ridge. Hilum terminal, with persistent funiculus remnant to 0.1 mm long; chalazal end obtuse, brownish-black and granular. Testa straw-colored to dark beige, with glistening, fine, dense horizontal striations between ridges. Embryo axile-linear, extending to both poles; endosperm readily visible.
Seeds develop from an anatropous ovule, characteristic in the Pontederiaceae, resulting in both ends being distinctly featured. The chalazal end is opposite the hilar end. The extension of the embryo to both poles is unusual; this is found only in the Pontederiaceae and from Ammomum in the Zingiberaceae.
Eichhornia crassipes (Sw.) Kunth (non-FNW)
Heteranthera limosa (Sw.) Willd. (non-FNW)
Eichhornia azurea (Sw.) Kunth
Monochoria hastata (L.) Solms-Laub.
South and Southeast Asia, from Iran to the Philippines and Indonesia, China, Korea, Japan, Taiwan, northern Australia, Fiji, and the Solomon Islands; United States
native to tropical Asia
freshwater pools, stagnant backwaters, mudflats, swampy places, ditches, along canal banks, in rice fields
Monochoria vaginalis is an attached aquatic annual or perennial herb with emersed leaves, to 50 cm tall. More widespread than M. hastata, it is a serious weed of rice fields in much of eastern and southeastern Asia. Dense colonies in shallow water may considerably reduce yields. Propagation is by whole plants or seeds. The entire plant (except the roots) is eaten as a vegetable in India, and the roots are used medicinally. Monochoria vaginalis may have been introduced to California as a contaminant in rice seed.