I stumbled upon a weird leafy vegetable in the Subantarctic Plant House in the Royal Tasmanian Botanical Gardens (RTBG). On an already chilly day I made my way into the still colder environment of the Subantarctic Plant House for a glimpse of the native vegetation of Macquarie Island. This special growing environment is kept chilled below 15ºC but above freezing and subjected to the gusty wind and mists that would be found on Macquarie Island, 1,550km south east of Hobart.
There among the tufts of coastal grass was a lush, leafy vine that looked for all the world like a pumpkin or zucchini. It was a joy to see such a vigorous, healthy and robust plant thriving in the cold southern winter. A closer look revealed a plant that’s well adapted to the cold with a covering of fine hairs across its large rounded green leaves.
The Macquarie Island cabbage (Stilbocarpa polaris) grows naturally on the coastal slopes of Australia’s southern-most island, Macquarie Island and also on New Zealand’s subantarctic islands. It can grow to a metre in height creating a canopy across the ground that helps to shelter nesting seabirds including penguins. The large leaves have evolved in response to the low light levels of the subantarctic as large leaves are needed there to photosynthesize.
It is one of the island’s megaherbs along with Pleurophyllum hookeri, a silver-leafed member of the daisy family. Macquarie Island cabbage is a member of the Araliaceae (the ivy family).
Mark Fountain, Deputy Director, Collections and Research at the RTBG has visited Macquarie Island and says seeing the megaherbs in their natural habitat is one of the real plant experiences.
He explains that as well as having large, handsome, hairy leaves the Macquarie Island cabbage produces tall heads of greeny-yellow pom-pom flowers. Flowering only occurs every three years or so in a mass flowering occurrence known as ‘masting’. After flowering the plant sets seed. A species of fungal gnat is thought to pollinate the flowers.
While the Macquarie Island cabbage is thriving in Hobart, this important native plant was under threat by introduced rats and rabbits in its native habitat. After a prolonged eradication program these feral animals were finally removed completely from Macquarie Island in 2011.
The Macquarie Island cabbage gained its common name as it was harvested as a vegetable by early explorers and sealers. They ate its vitamin-C-rich leaves to ward off scurvy in a world that was short of fresh fruit and vegetables. They must have needed that vitamin C as Macquarie Island cabbage isn’t easy to eat. As well as the hairy covering on its foliage, its edible stems are fibrous making them tough to prepare and eat.
Some 30 years ago, these plants were studied as part of a project on edible plants. The head of the project back then, Iain Dawson, described the vegetable as difficult to eat. He said records from the 19th and early 20th century revealed that sealers scraped the stalks and roots, chopping them finely to add to a stew.
We won’t be eating any for a while. It isn’t available to buy in Australia and has yet to be trialled outdoors in Hobart.
To see the Macquarie Island cabbage, visit the Subantarctic Plant House in the Royal Tasmanian Botanical Gardens in Hobart between 8am and 5pm in winter. For a glimpse of Macquarie Island in real time look at Macquarie Island webcam.
[This blog was first published on July 25, 2015 in TasWeekend, a supplement to The Mercury]