Friday, 18 June 2010

Kerguelen’s Land Cabbage*



Sir Joseph Hooker
(Director of the Royal Botanic Gardens Kew from 1865 to 1885, President of the Royal Society and recipient of numerous honorary degrees and medals) was so taken as a child by seeing pictures from Captain Cook’s visit to Kerguelen Islands, that he remembered thinking ‘I should be the happiest boy alive is I would see that wonderful arched rock, and knock penguins on the head’.

Luckily Hooker became a botanist and when he finally visited the French-administered Kerguelen Islands he was keener on finding new plants species. Kerguelen Islands, all 300 of them, are about 5,000 km south-east of Africa. The main island is more than 6000 square km but the rest are much, much smaller.

Cook had recorded only 18 species of plant on his 1776 visit. Hooker collected 30 species on his first day ashore and over a few months he made a list of 150 species, although he was also collecting lichens, mosses and the less conspicuous ‘plants’.

Curiously the flora is more similar to that of South America than Africa due to historical connections with Gondwana, but there are a few links to New Zealand.

Hooker was most excited by a plant called Kerguelen’s Land Cabbage, Pringlea antiscorbutica. As the species name suggests this plant was eaten, as a vegetable, to help prevent scurvy.

Hooker remarked that is almost seemed to have been ‘planted by Nature’s hand for the poor mariner’ – there were not other plants that looked similarly edible on the island.

In correspondence with Charles Darwin, Hooker asked the obvious question – why didn’t this distinctive plant grow on lands older than this one formed by a volcano? Clearly it had become extinct elsewhere, part of the process of natural selection documented by Darwin. It was later found on other subantarctic islands such as Heard Island.

So what is this Land Cabbage? Well, it’s actually a kind of cabbage. At least it is in the cabbage family, the Brassicaceae.

It’s such a windy place that the insect pollination used by most cabbage relatives is too difficult and the plants are self-pollinating. This means there is less variety and less options for adaptation should the environment change, although rabbits are its biggest threat at the moment.

Surprisingly for a plant that grows naturally at 50 degrees south, an article on the Australian National Botanic Gardens website suggests we could probably grow Kerguelen’s Land Cabbage in much of Australia.

The botanic gardens in Hobart struggles to grow it in subantarctic conditions so I think it would be tough one to grow here, but perhaps Mount Tomah would be worth a try. We do of course have plenty of other cabbage family relatives in our Herb Garden at Sydney, and some in our ornamental gardens like the Rock Garden at Mount Tomah.

For further reading on Hooker and his travels, see Imperial Nature by Jim Endersby (The University of Chicago Press; Chicago).

*This Passion for Plants posting will also appear on the ABC Sydney website (under 'Weekends' or search 'gardening'), and is the gist of my 702AM radio interview with Simon Marnie on Saturday morning, between 9-10 am.

Image: The Rock Garden at Mount Tomah with plenty of cabbage family plants but no Kerguelen's Land Cabbage

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