my cabbage-tree!, excl. — Green’s Dictionary of Slang

my cabbage-tree! excl.

[cabbage-tree hat, a hat made of woven cabbage-tree or cabbage-palm leaves]

(Aus.) a mild excl., synon. with my hat! excl.

1859		H. Kingsley Recollections of G. Hamlyn (1891) 196: ‘Oh my — (colonial oath!)’ said the other; ‘oh my — “cabbage tree!’” [Ibid.] 313: ‘Why, darn my cabbage-tree,’ he said.
1955		N. Pulliam I Travelled a Lonely Land (1957) 236/1: my cabbage tree! – an exclamation of no particular meaning.