Starfruit (Damasonium alisma)

KingdomPlantae
PhylumAnthophyta
ClassLiliopsida
OrderAlismatales
FamilyAlismataceae
GenusDamasonium
SizeHeight: 5-30 cm

Classified as Endangered in the UK.

Starfruit is so named because of the distinctive fruits this plant bears which appear as six-sided stars. The plant's appearance depends on the water level of the ponds where it grows. If the water level is high, starfruit retains its aquatic growth form with floating leaves produced on the end of long wiry stalks. When the water level drops sufficiently to expose the plants, previously floating leaves shrivel and are replaced by shorter tougher ones. The flower comprises three white petals which are shiny yellow at the base and the anthers appear large and yellow. The number of fruits produced can vary from just a couple to more than 20, depending on the size of the plant.

Starfruit is found in southern and south-western Europe where it is not considered rare, but in the UK it has always been uncommon. Its former range was restricted to a few counties in the south-east with occasional records in the Midlands. During the 20th Century it has declined considerably and by 1980 it was only known from one pond. Following the implementation of management works and regular monitoring to ponds where it was formerly recorded, starfruit has been re-discovered in more than half a dozen ponds during the 1990's, mostly in Surrey and Buckinghamshire.

Starfruit is largely associated with ponds that occur on commons or village greens, as it has a requirement for periodic disturbance such as that resulting from the trampling effects of grazing animals. It also appears to prefer shallow, saucer-shaped ponds with fluctuating water levels, often on gravel with little or no organic layer. It does best in places with open vegetation, lack of shade and areas of bare soil.

In the wild starfruit is usually an annual plant but under cultivation it has been known to live for up to three years. The seeds germinate below the water in early winter and the young plants resemble a tuft of grass. It flowers between June and August and the number of flowers produced is related to the time the mud remains moist. If the mud dries quickly, only a single flower may be produced before the plant dies.

The plant is variable in appearance depending on water levels. If conditions suit, starfruit can grow to become a large plant with up to 150 flowers. These are capable of self-pollination but it is thought likely that cross-fertilisation occurs as the flowers are popular with beetles and hoverflies.

The seed capsules look like six-pointed stars. The seeds can germinate quickly but most remain in the mud at the bottom of the pond. It is the seeds' ability to remain dormant for extended periods, suddenly germinating when the right conditions are present, that allow the plant to dramatically re-appear when the pond has been disturbed.

Starfruit has never been common in Britain, being largely confined to a few localities in the south-east. The plant declined spectacularly in the 20th century and by 1980 was only known from one pond. This was no doubt due to the neglect and lack of management of ponds and changes from traditional methods of watering livestock. The growth of competing plants is thought to have choked out starfruit which needs open vegetation. Many ponds will also have suffered a decline in water quality; starfruit has a requirement for high water quality and low nutrient levels. In addition, ponds were filled in or managed for angling interests with a constant water level instead of the fluctuating levels preferred by this species.

Starfruit is included in English Nature's Species Recovery Programme and Plantlife's Back from the Brink project. Originally, the project attempted a programme of re-introduction into suitable ponds within the plant's former range. However, this enjoyed little success and it was as a result of the activities of a commons preservation society that the secret of starfruit's recovery was discovered.

This preservation society in Buckinghamshire had decided to restore their village pond and had set about clearing the accumulation of weed and rubbish from the bottom. In doing this, they disturbed the mud and, a few weeks later, a local botanist noticed the re-appearance of starfruit. The seeds which had lain dormant in the mud of the pond for many years had germinated.

Plantlife experimented by disturbing other ponds nearby and found that starfruit appeared within a relatively short time. This early success led to a change of policy with regard to the recovery programme and efforts have been concentrated on discovering more about the precise conditions required by the plant.

Starfruit has been a victim of changes in human activity. It has declined due to changes in the way we interact with our environment. The aim of the recovery programme is to re-create the conditions needed to return a rare and unusual but important native species back to a state where it remains part of our natural heritage.

See also:
http://www.plantlife.org.uk

Information supplied by English Nature.

http://www.english-nature.org.uk