Damasonium
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 D. californicum | ||||||||||||
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Damasonium is a genus of aquatic plants, commonly known as starfruit and (older name) thrumwort.
Damasoniums are aquatic perennial herbs. The leaves are all basal, floating, or aerial in subterrestial plants. The flowers are hermaphrodite, in 1-many whorls, in umbels, racemes or panicles. Stamens 6. Carpels 6 - 9, in 1 whorl, connate at the base, each with 2 - many ventral ovules; The styles are terminal. The fruit are whorls of follicles; the follicles are laterally compressed, stellately radiating, with a more or less elongated apical beak.
Species
- D. alisma Mill.
- Synonyms: D. stellatum Thuill.; D. polyspermum Cosson; D. constrictum Juz.
Ecology
D. alisma - Acid ponds. Went into decline along with the village pond. It once grew in many English counties from Sussex north to Shropshire, but by 1900 was reduced to two ponds in Buckinghamshire and one in Surrey. Starting gradually to make a come back due to intense conservation efforts.
It seems to need open, well-lit shallow water to grow in and regularly churned up mud for its seeds to germinate.
Very variable in form according to the depth of the water it is growing in. Dwarf plants with aerial leaves occur growing sub-terrestrially on mud. The number of ovules vary. Usually there are 2 in each carpel but carpels with 4 - many occur over the range. Multi-ovulate forms from S.W. Europe and Sicilia wrre originally described as D. polyspermum.
The shape of the follicles depends on the number of seeds : the beak (empty upper part) of the carpel is elongated in 2-seeded plants, whereas in many-seeded plants the seeds occupy more of the follicle and the beak is relatively shorter and less well defined.