Here is a plant I wouldn’t have dreamed of promoting even two weeks ago in the heat and dry. A wetland plant!
Any of you with a dam, frogpond or even aquarium, may be familiar with an introduced primrose that can sprawl across the surface of the water and grow up from the shallows, with a 5-petalled yellow flower about the size of a 20-cent coin. This immigrant is known as Water Primrose, Ludwigia peploides and may even be considered problematic in some places.
The Native Primrose Ludwigia octovalvis prefers wet-land rather than being an immersed waterplant. It is a fast grower that forms a rounded shrub typically 1-2m high at maturity. In natural settings it develops quite a spindly look as it booms in growth during the wetter times then defoliates and even senesces at the extremities in dry spells. Come the next wet phase though and it will regenerate from its woody base or trunk. It has yellow flowers but only four petals, not 5 like its exotic relative.
The growth habit of L. octovalvis makes it suitable for a range of applications in wet or waterlogged soils. Its fast growth and matted roots will help stabilise the soil surface and act a as a good water ‘pump’ to transpire moisture from the soil into the air. It will perform well to ‘capture’ a site in locations that may typically be planted with slower growing plants like Lomandra longifolia or Waterhousea floribunda and could even work effectively as a ‘companion’ to such slower species, assisting in the displacement of more aggressive exotic grasses.
Individual plants of L. octovalvis may only live a few years, but they are quite capable of self-seeding and maintaining a viable population once established. I have seen them form a rich stand interspersed with other sedges and rushes in a soak/overflow below a dam, creating a great sediment trap and wetland habitat. Of course, once taller plants become established and shade an area, L. octovalvis will gradually die out.
In more landscaped settings, the vigorous growth of L. octovalvis can be harnessed through regular tip-pruning to maintain a bushy growth form, perhaps with seasonal pruning of woody stems to keep it to a preferred size. As long as good soil moisture is maintained L. octovalvis can provide extended cycles of flowering through most of the year.
The Latin species name octovalvis refers to the eight valves or segments in the seed pod which is a slender capsule about 5 cm long that dries to a dark-brown colour and then splits open to reveal many tiny seeds. The species has a pan-tropical distribution and perhaps traditional medicinal uses in various parts of the world.