mass exodus

Animal, vegetable or mineral? The origin of this jelly-like substance may surprise you, says MARTYN ROBINSON

Recently, a gardener asked me to identify lumps of a strange, jelly-like substance that appeared in his garden after heavy rain. It looked vaguely like frog spawn, except it wasn’t in water, and there didn’t seem to be any eggs within the amber or yellow masses. Luckily, a botanist told me the answer to this conundrum about 20 years ago, and I mentally thank him each time it reappears. It’s not frog spawn or anything to do with an animal, it’s not a strange jelly fungus (although some smaller fungi do look a bit like this), no, it’s actually sap from the kurrajong trees in the genus Brachychiton. This genus includes the Illawarra flame tree (above), Queensland bottle tree, kurrajong, lacebark kurrajong and dwarf kurrajong, as well as a number of other trees that are less well known.

These splendid garden trees are remarkably good at surviving drought conditions. All of ours survived the last dry, baking-hot summer, while larger eucalypts nearby either died or looked the worse for wear. Part of the strategy seems to be this strange, jelly-like sap, which can absorb lots of water when it’s available, swelling like a jelly. However, when there has been a long, dry spell followed by a deluge, sometimes these trees absorb so much water that the sap bursts out of the trunk – seemingly under pressure – and drops to the ground, often some distance from the tree. By morning, the points where the sap has been ejected from the tree have healed, to the extent that they are often almost unnoticeable, leaving the bewildered gardener with this strange substance to try to identify. So now you know, if you ever come across this substance, to check for a kurrajong nearby!