Allocasuarina in flower

Scrub Sheoak

Allocasuarina paludosa

This plant is also known as the Scrub or Swamp Sheoak. The ones in the Reserve are not found so much where the reservoir or watercourses are but in the north-western facing areas, in more open sections of forest. The name Scrub Sheoak seems more appropriate here.

It can be an unassuming plant: you can easily miss it walking through the Reserve. It has long fine branchlets, wiry and articulate, and these sway in the breeze. The female flowers, though, are distinctive. These can be found flowering, on and off, throughout the year but do seem to be more so during winter and into spring.

Deep red flowers, in close against stem

The male flower have begun to develop in the last couple of weeks and their colour, too, really stands out against the deep or grey green of the branchlets. The spikes occur at the ends of branchlets. If something brushes against the bush, you can see the pollen spread quite readily. This is how fertilisation occurs, in the wind.

Male flowers, orange-brown

The fertilised flower develops into a cone and each seed is enclosed in a pair of valves. The cones of the Allocasuarina paludosa begin as the same brown as male flowers and then go grey as they get older. They also have an arrangement of valves that distinguishes this plant from other species in the family.

Egg-shaped cones, with pointy bracts at the base of each valve

Crowded cones

The valves have opened in this case and the seeds – called samaras – have fallen down to the forest floor

Some species of Allocasuarina – there are at least 13 in Victoria – have separate male and female plants; some have both on the same plant. This species is known for both conditions. Most of the plants in the Reserve are either male or female and there are only a very few that are both.

This plant is both male and female – monoecious

Identifying features – the number of teeth in the whorls (leaf laminae) and appearance of the articles (the longitudinal ridges)

What makes these plants unusual in appearance (compared to the other flora we find) also ensures they are very well adapted to their environment. These plants’ ancestors could be found in Gippsland when the climate was much wetter and warmer and have survived the progressive drying (see this publication (p.508) for a diagram that illustrates the processes – which included Casuarina –  that shaped the coal measure deposits in the Latrobe Valley, for example). The reduction in leaf size to a tiny whorl of teeth, a highly modified leaf base in the form of the strands running along each segment of the branchlets you can just see in the image above, and the plant’s stomata found in the furrows between add to this plant’s resilience in dry conditions. These are adaptations have allowed this group of plants to survive and spread over millions of years as Australia’s environment has become progressively more arid (see Steane, Wilson and Hill, 2003).

There’s beauty in that.