The Busy Bursaria*

Senior Ecologist Doug Benson and co-workers at the Botanic Gardens have been studying some remnant pieces of woodland at Mount Annan Botanic Garden for the last 21 years or so (from when the Garden was opened).

You can read all about it on the web – find our botanic gardens site and then click through Science, Research and then Ecology of Cumberland Plain Woodland.

As Doug says on the website, Cumberland Plain Woodland once covered about 125 000 hectares on the clay soils of western Sydney, from Kurrajong across to Picton. Clearing for farming and urban development have reduced it to a few small remnants today, many of which are under threat. The whole community is now listed as an Endangered Ecological Community.

This woodland isn’t the most beautiful pieces of vegetation to the untrained eye. It’s often dry and sparse, with few big showy flowers. If look closely though, there are lots of fascinating plant and animal stories.

One of the common species in this community is the Sweet Bursaria or Blackthorn, Bursaria spinosa. It’s a stiff, prickly shrub which can live up to 60 years. The flowers are small and white, and the dry fruits shaped like a purse.

In February, Sweet Bursaria is in full flower and perfume, and it’s very sweet! (Bursaria is in the same plant family as the native Pittosporum, another sweet-smelling plant.)

When in flower, Sweet Bursaria attracts lots of insects, including butterflies, moths, bees and beetles. A native bee is the usual pollinator and the Pittosporum Beetle, named from its association with that close relative, is a frequent visitor at Annan – this bug has a distinctively bright red head and underbelly.

I remember Sweet Bursaria well from when I lived in Victoria. At places like Castlemaine (where my parents still live), the rare Eltham Copper Butterfly depends on Sweet Bursaria for its survival. Eggs are laid on the shoots and stems of the Bursaria, and the larvae eat some of the leaves while being attended by local ants (who feed off secretions of sugar and other bits and pieces from the larvae, and in return probably destroy nasty fungi and bacteria). The adult butterflies then feed on the nectar produced in the Bursaria flowers.

The nectar, as well as the insects, also attracts plenty of birds. And small birds, like the Blue Wren, can nest safely in the prickly branches.

For humans, the leaves contain an oil called aesculin. Aesculin absorbs ultraviolet light and the leaves were rubbed onto skin by early settlers to help prevent sunburn.

It’s a tough plant, and after fire the shrub resprouts from a large tuberous root. Doug Benson’s team has confirmed, among other things, that seedlings are established mostly during extended rain periods and that rabbits enjoy eating them.

Image: Pittosporum Beetle on Sweet Bursaria (photo Lotte von Richter). *This Passion for Plants posting will also appear on the ABC Sydney website (possibly under 'gardening'), and is the gist of my 702AM radio interview with Simon Marnie on Saturday morning, between 9-10 am.