Helanthium tenellum
Helanthium tenellum, the pygmy chain sword, is a species of plants in the Alismataceae. It is native to the eastern United States, southern Mexico, West Indies, Central America, South America
Description
The leaves of H. tenellum are narrowly elliptical or lanceolate. At different times during the plant's life cycle, the blade of the leaf is scarcely distinguishable from the petiole, while at other times the petiole is 10 to 15 times as long as the blade, which may be 1–4 cm long and 0.2–1 cm wide, with a pointed tip. The base is decurrent to the petiole and has between one and three veins.The stem is thin, erect, often curved, and may be 3–20 cm long. In small plants, the stem ends in a single inflorescence ; in larger plants the inflorescence is racemose, composed of two whorls placed one above the other. Bracts are free and 2–6 mm long in the first whorl. Pedicels are 1–3.5 cm long. Sepals are 3 mm long, membraneous, and usually have five fine ribs. During ripening, the sepals enlarge and reach a length of up to 6 mm and fully cover the aggregate fruit. A specimen may have six to nine stamens, each about 1 mm long. Anthers are 0.25 mm wide by 2.25 mm long, which is three times shorter than the filaments. It may have sixteen to eighteen pistils. The achenes are compressed, and arched in the apical part; they are – 1.1 – mm long, and black, with three lateral ribs. The basis of the stylar beak is under the level of the tip of the nutlet and may be 0.1–0.3 mm long.
It propagates by sending out runners and will also flower when grown emersed.