Helanthium tenellum 'parvulum'

In the hobby known as a light green form of Helanthium tenellum (Echinodorus tenellus); probably imported from North America. Newer molecular data suggest the North American type may be regarded as a separate species, Helanthium parvulum. Two forms are in cultivation: one, with narrower leaves, grew in a botanical garden from the 1950s to the 2000s and was common in the countries of the former Eastern Bloc, now nearly lost; the other — with leaves wider than 2 mm and up to 10 cm tall — was common in Western Europe and is now making a comeback as Helanthium parvulum '2' and H. tenellum 'Broad Leaf', including from tissue culture.

Difficulty medium, growth medium, light medium to strong, CO₂ 20–40 mg/l, temperature 18–26 °C. Forms a lawn, propagates by runners.

Nano aquarium, foreground in a group and as a carpet.

Decades ago this very form was sold under the name Echinodorus tenellus — until the current H. tenellum, with olive-green to reddish, very narrow underwater leaves (probably from the tropics of South America), appeared on the market. In recent years the broad-leaved form has been mistakenly sold as 'Ranalisma rostrata'; the true R. rostrata from Southeast Asia looks very similar underwater but is clearly different once it flowers above water.