Eichhornia heterosperma

The different-seeded water hyacinth, Eichhornia heterosperma, is widespread in tropical America and looks very similar to the species Eichhornia azurea. It can only be distinguished reliably from E. azurea by floral characters.

According to Kasselmann (2010), Eichhornia heterosperma has not yet been introduced as an aquarium plant. Plants labelled E. heterosperma are indeed passed on in the aquarium hobby, but they are probably always misidentified. At least, we know of no reliable evidence that any aquarium plant is E. heterosperma.

One plant passed on as “E. heterosperma” turned out to be a red-stemmed form of Eichhornia azurea. Another plant labelled “E. heterosperma”, which was collected in Ecuador, forms roundish, heart-shaped floating leaves at the water surface and apparently belongs to Eichhornia diversifolia.

In true Eichhornia heterosperma the flowers are smaller than in E. azurea. All six petals have a smooth margin, and there is no yellow spot on the uppermost petal (in E. azurea three of the six petals have a fringed margin, and the uppermost petal has a yellow spot). The inflorescence stalk (peduncle) is smooth in E. heterosperma and glandular-hairy in E. azurea.

Otherwise both species have roughly the same appearance: they form long, strong shoots floating in the water, with leaves arranged in two rows. The emersed leaves are spoon-shaped, long-stalked and project out of the water. Submersed shoots have linear underwater leaves. E. heterosperma is reported to have a red stem.

In Eichhornia diversifolia the flowers are likewise smaller than in E. azurea and have no yellow spot on the uppermost petal, but at the water surface E. diversifolia does not form spoon-shaped aerial leaves projecting out of the water as E. heterosperma does, but distinctly heart-shaped floating leaves.

Perhaps Eichhornia heterosperma would be just as suitable as an aquarium plant as the similar E. azurea. It would be very interesting to introduce true E. heterosperma and to compare it with E. azurea in aquarium culture.

- To be continued -