Hygrophila costata is a variable species. Several authors also count H. guianensis and the North-American H. lacustris among it. H. costata originates from the American tropics and subtropics, however, it has been introduced into Australia (Queensland) by the aquarium plant trade and is considered an invasive plant there today.
The stems of the emersed form of H. costata are hairless or have very short hairs (not glandular), the leaves are lanceolate, shaped like a willow leaf, and the small white, 1 cm long flowers stand in groups of up over 10 in the leaf axils. The flowers are followed by spindle-shaped acuminate densely grouped fruits.
H. costata, of American provenience, is quite similar to the plants of the Hygrophila salicifolia complex from Asia. However, it differs from them by its white flowers, among others. Hygrophila salicifolia has light purple to pink flowers.
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