Damasonium alisma

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Damasonium alisma, commonly known as starfruit, is a small marsh flowering plant in the Alismataceae family. It is listed as Near Threatened by the IUCN. Its native range includes parts of Europe and Asia, including the British Isles.

In Britain, it was once common in ponds across the south and central parts of England, but numbers declined as pond habitats disappeared. By 2006 it had not been recorded in the wild and is considered endangered in the UK. In 2013, seeds from the extinct Headley Heath population were germinated in ponds managed by Surrey Wildlife Trust, and the plants have grown there each year since (at least up to 2018).

Damasonium alisma grows in acidic ponds and needs open, well-lit, shallow water with churned mud for its seeds to germinate. The plant varies in form depending on water depth—some forms are small and grow under the mud, while others have visible leaves.

Usually there are two ovules per carpel, but there can be four or more. The shape of the seed pods changes with the number of seeds they contain: two-seeded pods have a longer beak, while many-seeded pods are fuller.

Taxonomy: Carl Linnaeus first described it as Alisma damasonium in 1753, and it was moved to the genus Damasonium by Philip Miller in 1768. The species has many synonyms from its taxonomic history.