Species of the Month: October

Pobblebonk Frog (Limnodynastes dumerilii)



Named for its unusual call, the Pobblebonk Frog, also known as the Eastern Banjo Frog (Limnodynastes dumerilii) is common throughout our city's suburbs. You may find one in a backyard pond, or even in a garden bed while digging! 

The Pobblebonk is found throughout Victoria and Tasmania, but also west to Adelaide and north along the coast of New South Wales. One subspecies, L. dumerilii dumerilii is found throughout the northern and western suburbs of Melbourne, while L dumerilii insularis is found throughout the eastern and southern suburbs. Eastern Banjo Frogs  inhabit a range of environments, including woodlands, rainforests, farmlands, coastal areas and urban regions. These frogs live in and around the still water bodies found in swamps, dams streams and lakes. 

The Pobblebonk Frog can be up to 85mm long, often with a warty appearance that can cause them to be confused for the dreaded Cane Toad (Rhinella marina). They can vary greatly in colour, ranging from dark browns and blacks to olive green. Pobblebonks have a pale, yellow stripe from the eye to the top of the front leg and there may also be a pale stripe down their back.  This species lacks webbing between the toes, but has a shovel-like toe on each rear foot to aid them in burrowing. The most defining features of the Pobblebonk include a prominent tibial gland on the lower portion of each rear leg, and fleshy metatarsal tubercles  (fleshy lumps) on each hind foot.

Mating occurs from August all the way through to April. Females are able to lay up to four thousand eggs, which they deposit into a large, white, floating raft that made from mucous and bubbles. These rafts are usually found concealed in aquatic vegetation. Depending on water temperature (which affects metabolic rates), tadpoles can take up to fifteen months to fully develop. When they hatch, pobblebonk tadpoles are large, dark brown or black, with dark grey or brown fins.

This species of frog has a call that sounds like a plucked banjo string: a resonant ‘bonk’ sound. Nearly all year round these calls can be heard, especially after heavy rains. Males call every few seconds, usually from the shelter of floating aquatic vegetation, but also less regularly from the waters edge. During dryer spells, Pobblebonks will burrow themselves into the ground with their well equipped back feet, and wait for rain. 

Author: Emma Walsh

White Cypress-Pine (Callitris columellaris)



Many Melbournians are familiar with the ornamental juniper and fir trees that you find in many suburban gardens, or with the pine trees that we decorate at Christmas time. These are all foreign species, however there are a few gymnosperm species that are native to Victoria. Furthermore, there is just one gymnosperm that is indigenous to Melbourne: the White Cypress-pine (Callitris columellaris).

What is a gymnosperm I hear you ask? Gymnosperms are the primitive cousins of the flowering plants, the angiosperms.  They differ to flowering plants in that they do not produce flowers and instead produce cones, and that the ovule is not enclosed in an ovary. In species that are monoecious (hermaphroditic) individuals bear both male and female cones, while in dioecious species male and female cones are only found on individuals of their respective genders. Male and female cones are easily distinguished by their size: the male, pollen-producing cones are smaller than their female, ovule-bearing counterparts. Gymnosperms rely mostly on wind pollination, not insect pollination like many flowering plants.

There are four plant phyla that represent the gymnosperms, and by far the largest and most diverse is the Coniferophyta. Also known as conifers, members of the Coniferophyta are monoecious, deciduous (or evergreen) and have needle- or scale-like leaves. Some of the better-known conifer groups include the spruces, firs, pines and redwoods. Victoria is home to six conifer species, the Mountain Plum-pine (Podocarpus lawrencei), the Port Jackson Pine (Callitris rhomboidea), the Black Cypress-pine (Callitris endlicheri), the Scrub Cypress-pine (Callitris verrucosa), the Slender Cypress-pine (Callitris preissii), and of course, the White Cypress-pine (Callitris columellaris).

The White Cypress-pine (also known as Callitris glaucophylla) is a slender, conical tree with a single straight trunk with thick greyish bark and scale-like leaves. It’s female cones are relatively small and round, while it’s male cones are so small that they appear to be the dead ends of the leaves. The White Cypress-pine was originally widespread across Australia, but its distribution has been altered post-European settlement by domestic livestock and feral animal grazing, altered fire regimes and invasive weeds. Today its distribution is largely fragmented, with much of it’s Victorian range managed as forest reserves. White Cypress-pines are indigenous to the northern suburbs of Melbourne, namely Maribyrnong, Diggers Rest and Bulla. The good place to find the White Cypress-pine in its natural habitat is in the Organ Pipes National Park in Keilor North, northwest of the CBD.

This species is generally found in areas with sandy, well-drained soils. It does not survive in finer soils due to its susceptibility to water logging.  White Cypress-pines are extremely drought tolerant, and often develop fine ‘feeder roots’ in the upper few inches of soil for added water absorption. Although this species is hardy in dry conditions, it is sensitive to fire. Tree crowns will not regenerate and seed output can be suppressed for up to five years after being damaged by fire. Seedlings are also vulnerable to fire, as well as introduced herbivores such as sheep, goats and rabbits.

In the past aboriginal communities have used the timber of the White Cypress-pine to make spears, spear throws and paddles, and have mixed its resin with kangaroo dung to create an adhesive. It’s bark and foliage were also used as insect repellent.

It is easy to overlook conifers when considering iconic indigenous plants because they aren’t as pleasing to the eye as their angiosperm counterparts, but I find them fascinating because of the way they endure and persist in an environment where flowering plants are so dominant. White Cypress-pine is our ONLY indigenous gymnosperm, stoically holding its own against the countless angiosperms that call Melbourne home. 

Author: Emma Walsh