Damasonium is a genus of aquatic flowering plants in the family Alismataceae (order Alismatales), commonly known as starfruit, or by the older name thrumwort. The genus was described by Philip Miller in 1754, without designation of a type species, and comprises around six accepted species distributed across scattered temperate and Mediterranean regions of the world.
Plants in this genus are perennial herbs of shallow water and mud, typically found growing at pond margins. Leaves are all basal, either floating on the water surface or held aerially where plants grow on exposed pond edges. The flowers are hermaphrodite, arranged in whorls that form umbels, racemes, or panicles, each with six stamens and six to nine carpels joined at the base in a whorl, every carpel containing two to many ovules on its inner face and topped by a terminal style. After flowering, the fruit develops as a whorl of follicles that spread outward in a star-like (stellate) pattern, each one flattened from the side and tipped with an elongated beak — a distinctive fruiting structure that gives the genus its "starfruit" common name.
The genus has a subcosmopolitan but markedly patchy distribution. Damasonium alisma is found across much of Europe and into western Asia, from Great Britain, France, Portugal, Spain, Italy and Greece through Russia, Ukraine, Moldova and Kazakhstan. Damasonium bourgaei spans the Mediterranean Basin and extends to India, while Damasonium polyspermum is concentrated in the western Mediterranean and North Africa (Spain, France, Portugal, Greece, Sicily, Algeria, Libya, Morocco). Damasonium californicum is restricted to the western United States, and other species occur in Kazakhstan and Siberia's Altay region, and in Australia — a scattered, disjunct pattern typical of ancient wetland-plant lineages.
Distribution
Damasonium has a subcosmopolitan but very patchy distribution. D. alisma ranges across Great Britain, France, Portugal, Spain, Italy, Greece, Russia, Ukraine, Moldova and Kazakhstan; D. bourgaei spans the Mediterranean Basin and India; D. californicum is found in the western United States (Idaho, Oregon, Nevada, California, Montana, Washington); and D. polyspermum occurs across Spain, France, Portugal, Greece, Sicily, Algeria, Libya and Morocco. Other species reach Kazakhstan/Siberia's Altay region and Australia.
Ecology
Species of Damasonium are aquatic perennial herbs growing in shallow water or mud at pond margins. Their leaves are all basal, either floating on the water or held aerially where a plant grows on exposed pond edges, reflecting a habit adapted to fluctuating water levels.
Taxonomy Notes
The genus was first described by Philip Miller in 1754 (Gard. Dict. Abr. ed. 4), with no type species designated at that time. It is placed in family Alismataceae, order Alismatales, per GBIF's Backbone Taxonomy.
