Helanthium bolivianum 'Angustifolius'

Light green ribbon-like underwater leaves 3–4 mm wide and up to 50 cm, sometimes over 60 cm long; under strong light they are usually shorter. It resembles Vallisneria nana. Above water it is much shorter and resembles the other forms of the group: leaves 6–15 cm long and 6–10 mm wide.

Undemanding, but needs trace elements: it pales when iron is lacking, helped by root fertiliser and generous feeding through the water. Strong light and CO₂ speed up growth but are not required — it also suits dimly lit tanks without CO₂, where it grows more slowly. It propagates by runners; once established it spreads avalanche-fashion and needs controlling — young plants up to 20 cm tall appear virtually overnight. It flowers under a short day, and under a long one (more than 12 hours of light) it mostly produces runners. Light medium to strong, CO₂ 10–40 mg/l, temperature 20–26 °C.

Unlike other runner-forming sword plants, it does not suit a foreground lawn; but it is excellent for the midground, background and sides — a good substitute for Vallisneria.

Better known under the name Echinodorus angustifolius. It probably comes from the state of Mato Grosso (Brazil); by chromosome number it is a triploid form of H. bolivianum; in Europe since the 1960s, a relative novelty in the US. Another form is also sold under the same name Echinodorus angustifolius, one that stays noticeably shorter under the same conditions and forms denser rosettes.