Vallisneria 'Natans': grower data and a naming puzzle

What the grower data says

Tropica rates ‘Natans’ easy, with low light and CO2 demand and “high” growth, one of the few plants in its data with the top growth rating ^[1]. The description calls it a hardy plant for beginners with fine, narrow leaves, 50–100 cm long and about 1 cm wide, so it does not overshadow other plants much, and says it is easy to propagate using its many runners ^[1].

The height rating of 20–30 cm or more is the average after two months; the 50–100 cm leaf length in the description is the mature size ^[1]. Tropica’s article on ‘Tiger’ notes that in shallower tanks the leaves float on the surface and can shade the plants underneath ^[2].

A water plant, not a marsh plant

Most aquarium plants are grown emersed in nurseries. Vallisneria is an exception: Tropica’s article on emersed production names Egeria, Cabomba and Vallisneria as pure water plants ^[3], and its article on Vallisneria spiralis ‘Tiger’ explains that the genus is fully aquatic, will not grow emersed and is propagated under water ^[2]. That article’s notes on maintenance apply to the genus as a whole: runners form readily, trimmed leaves tend to rot at the cut, so whole leaves are better removed at the base, and off-cuts must not reach natural waterways ^[2].

Planting

‘Natans’ is sold as a bunch. Tropica’s instructions are to remove the anchor, split the bunch into separate plants, remove damaged leaves and plant them with some distance between them; roots develop soon after ^[1]. Runners then fill the gaps.

The naming puzzle

The label and the description do not agree. Tropica files the plant under Vallisneria americana ‘Natans’, gives its origin as Asia, and its description calls it “Vallisneria sp. ‘Natans’ from Asia” ^[1].

The World Checklist of Vascular Plants accepts Vallisneria americana Michx., in the frogbit family Hydrocharitaceae, as a North American species: its native range is 37 regions of the eastern and central United States and Canada, from Québec and Nova Scotia to the Carolinas and west to Washington and Oregon ^{[5, 6]}. The checklist also accepts a separate Asian species, Vallisneria natans (Lour.) H.Hara ^[4].

The grower does not say which species its ‘Natans’ belongs to, and the “sp.” in its description suggests it does not claim to know. This profile keeps Tropica’s name and its ratings, and flags the mismatch rather than resolving it.