New Zealand native plant that grows by runners over or just under the soil. It roots at the nodes.
Common name Swamp Musk.
Very easy to grow and control in the garden.
Flowers are a very interesting shape and and stand proud of the foliage. Depending upon situation you may get lots of flowers making a really attractive show. Grows naturally is cool moist areas at a variety of altitudes, but mainly lowland swamps in the South Island.
Under UV nightlight (which is the wavelength that night-flying moths view the world) the purple/blue colours light up like an airport runway lights drawing them in to pollinate it's flowers. (Thanks for the info Gerry).