Back to the plants this week! As we are going with the riparian flow for a while, I thought I'd feature a few of Illawarra's most water-loving or inundation-tolerant plants.
There are dozens of local water plants, living anywhere from periodically inundated creek lines to permanent waterways and the pools and soaks along them. They provide habitat for local frogs, lizards, insects and other fauna, so they're really important for biodiversity. If you take a wander along a relatively undisturbed stretch of a local waterway (often to be found in Council parks and reserves) you'll probably see a few of these plants.
One plant you're likely to see on almost any watercourse is Common Rush (Juncus usitatus). It is still common and widespread on local watercourses, and in other damp areas. It is an outstanding habitat plant, supporting frogs, birds and even freshwater crayfish, which eat the young stems as they grow.
If you see Common Rush growing near you, check out its leaves to see if there are any frogs, lizards or small birds hanging around. There are also several other Juncus species that occur in the Illawarra, most of them local natives, that provide similar habitat value.
Common Rush is fairly adaptable and can be found in soils that are usually wet or regularly inundated. This is part of the secret of its continuing success.
Many other species are more specialised in where they will grow, and this is especially true of the aquatic plants, those that require permanent moisture.
Some grow in soil in water of varying depths, while a few float on the surface. An example of the former Jointed Twig-rush (Machaerina articulata, formerly Baumea articulata). This tall, elegant-looking rush tends to occur in slower-moving water, up to about 80cm deep, and can tolerate some salinity.
A floating aquatic plant that is easily seen, and also widely available, is Azolla. Two species, Pacific Azolla (A. filiculoides) and Azolla (A. pinnata) occur locally, and can be found in still freshwater bodies and dominating many a garden pond.
The image below was taken at the gardens at Greenhouse Park in Port Kembla, but coastal wetlands and slow-moving creeks may also host Azolla; I saw some just the other day near the beach in Woonona.
As well as plants that require permanent water or permanently damp soil, there are many more that grow a bit further up the banks of creeks.
These include many familiar locals such as Spiny-headed Mat-rush (Lomandra longifolia), Sandpaper (or Creek) Fig (Ficus coronata), Cheese Tree (Glochidion ferdinandi) and Lilly Pilly (Syzygium smithii), and some lesser-known but beautiful trees like the Brown Beech (Pennantia cunninghamii) and the mighty River Oak (Casuarina cunninghamiana).
Tolerating drier soil than aquatic plants, they are essential elements of riparian ecosystems, helping to stabilise creek banks, absorb water into the soil and reduce the amount of water rushing through waterways during floods.
While little can withstand the very large flood events that occur in this region, as a general rule the more (local native) plants are present along a waterway, the better protected from erosion it will be.
About the writer
Emma Rooksby is a local volunteer bush regenerator and environmental educator who helped establish the Growing Illawarra Natives website. She is passionate about protecting and restoring local biodiversity in the Illawarra region and collaborates with many groups and individuals who share that passion.
