In two attacks over a 24-hour period, 13 of the valuable plants in the cacti house inside the winter garden glasshouse were beheaded and chopped in to pieces by someone using their metal plant labels as a weapon.
Plant collection curator Stephen Bishop said both attacks happened during the glasshouse's open hours - the first about 1pm on Thursday, the second between 10am and 10.30am yesterday.
He suspected the vandals were children, as broken parts of the cacti were left lying beside the plants.
He believed it was unlikely the culprits would be caught.
"I had just come in this morning with some new plants to replace the five destroyed yesterday and thought `heck', there's more, but then I realised it was a new lot. It's just crazy."
Usually shying away from publicity about vandalism of the collections, he wanted whoever was responsible this time to know their "fun" had done thousands of dollars worth of damage, Mr Bishop said.
Slow to grow and expensive to buy, some of the plants could be repropagated, but it would be years before they could be rehomed in the cactus house.
A South American Espostoa lanata, for example, which was five years old and would cost up to $300 to replace, was chopped in half, a metal plant label left lodged in its spine.
"This particular plant was donated by a cacti collector who donated it thinking it was going to a good home. It's a real shame."
Dunedin police are investigating the incidents.
