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Ludwigia octovalvis (Jacq.) P.H.Raven 1962
pronounced: lud-WIG-ee-uh ok-toh-VAL-viss
(Onagraceae – the evening primrose family)
common name: Willow Primrose
Ludwigia i s named for Christian Gottlieb Ludwig (1709–1773), German physician and botanist, remembered for his correspondence with Linnaeus concerning plant classification. He was Professor of Medicine at the University of Leipzig in Germany. This university was founded in 1409, and is still in operation today, with some 30,000 students. Linnaeus named this genus after him. Octovalvis is from the Latin octo-, eight, and valva, a leaf of a folding door, referring to the 8 valves of the fruit.
This pan-tropical plant is an erect, robust, often multi-branched herb, sometimes woody at the base, that usually grows to 1 m or more in height, in moist areas, rooting at the nodes. It is found in damp grasslands, rice fields, along ditches, in swamps, pools, river beds, on floating islands in lakes, and in coconut plantations, from sea-level up to 1500 m in elevation. It is often aquatic, with submerged parts bearing pneumatophores. The plant photographed was in Butler's creek at the northern end of Picnic Street.
The flowers are usually solitary, occasionally clustered, in upper leaf axils or in an inflorescence, often with bracteoles. The flower-cup does not extend beyond the ovary. They have 4 sepals that persist, 4 yellow petals and 8 stamens, and an inferior ovary. The petals of the flower soon fall off.
The tapering cylindrical capsule is thin-walled, pale brown with 8 darker ribs, usually about 4.5 cm long, but varies between 2 and 5.5 cm long, with the pedicel up to 1 cm long. It is irregularly dehiscent, the seeds being free or embedded in the endocarp.
Its close relative, the Long-leafed Willow Primrose, Ludwigia longifolia, is a native of South America, grows naturally from Brazil to Argentina, and is considered a major weed in its native range. It was introduced into Australia as an ornamental, and was first recorded as naturalized near Sydney in 1991. It has spread through much of the central coast region of NSW, and has been declared a noxious weed there. It has now reached as far north as Brisbane.
Another introduced species, the Peruvian Willow Primrose, Ludwigia peruviana , has also become a serious pest in the Sydney region, but it has not yet been recorded in Queensland.
Larvae of the moth Theretra silhetensis feed on this plant.
Photographs taken at Picnic Bay 2009-2016
Page last updated 232nd September 2018