h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

A few years ago I was hiking along with my sister and her husband (I think then still husband-to-be) in the Natal Drakensberg mountains. Those are the highest mountains in Southern Africa, and it was my first time hiking there. It was a marvelous experience to me. Not only the landscape was spectacularly impressive – so was the plant life. Up there, with minimal human disturbance, it was like the gardens of the gods. Especially interesting to me was how extremely luxuriant the foliage was. There were a great many large-leaved plants, especially in the gorges through which the multitudes of streams flowed. Some of them I recognized, such as some large lily-like plants, but some were totally new to me. Among these were some plants with the most incredible huge, round, pumpkin-plant-like leaves. I had absolutely no idea what they were – in fact I had no idea such plants even existed in this country.

What was amazing to me was that such large leaves should exist at such a high altitude – up there in the mountains the winters get very cold, with snow being frequent. The largest of those leaves were about half a meter in diameter, and that on a soft, low-growing herbaceous plant.

Back home I scoured books to try and find out what they were. At last I got them – they were the species Gunnera perpensa. I’d never heard of them before but now I would surely never forget.

It took me quite a while to learn more about Gunneras. They are pretty unique and in a family all of their own. Gunnera perpensa is the only species found in South Africa and it turns out to be very widespread, occurring in cool mountain habitats not just in South Africa, but through eastern Africa and also Madagascar.

When I read on a web page recently that Gunnera included some of the largest herbs on Earth, I was a tad skeptical. The ones I had seen were pretty impressive, but in some of the lushest rainforests I was sure there were bigger herbs.

I was right – and some of them are Gunneras too!

One of the nicest ones occurs in Hawaii. I remember years ago reading an article about the endemic flora of the Hawaiian islands, and there was an old photo showing some huge-leaved plants in the forest understory – photo taken from high above. I was very impressed but back then the caption didn’t say what they were. So I was delighted when I found them online and discovered they are relatives of the Gunneras we have over here.

Here are photos of the Hawaiian Gunnera petaloidea:

http://www.botany.hawaii.edu/Faculty/Carr/images/gun_pet_emt.jpg

From above, showing their lovely shape:

http://luirig.altervista.org/cpm/albums/bot-hawaii15/07290-Gunnera-petaloidea.jpg

Those are some pretty large leaves! However, there are species that are even bigger:

http://en.wikipedia.org/wiki/File:Gunnera_tinctoria_2.jpg

http://www.calfloranursery.com/images/pics/g_h/gunnera_tinctoria.jpg

Gunnera tinctoria of Chile can have leaves 2 m tall and wide. But there’s one even bigger than this:

http://www.exoterra.nl/paginas/hyp.%20gunnera.htm

http://www.mulu.co.uk/image_popup.php?image_id=123

Gunnera manicata of Brazil can have leaves 3 m tall and wide!

The South American Gunneras are sometimes called ‘poor people’s parasols’ since the leaves are large enough to shield a person from rain – and often used for that purpose by indigenous people.

Gunneras are apparently quite and old group – having arrived on the scene in the heyday of the dinosaurs, about 95 million years ago. Today they have what is called a ‘disjunct’ distribution over much of the world but particularly southern regions: South America, New Zealand, and Africa, with the one species reaching Hawaii. It is interesting that they seem to be able to handle a bit of cold, occurring in southern Chile, and being able to grow in Britain and southern USA. In South Africa, like I said, they occur high up in the mountains. Apparently here the large leaves do not survive the snow and frost in winter, but die back and re-sprout in the spring from their underground rhizomes. I don’t know what they do in the other cold places where they grow – presumably something similar.

Here’s an article on PlantzAfrica about our local Gunnera:

http://www.plantzafrica.com/plantefg/gunnerperp.htm

The species (and some of the others too) is called 'Wild Rhubarb' or 'River Pumpkin', though not being closely related to either pumpkins or rhubarb.

I was fascinated to find out the reason why Gunneras can grow so luxuriantly in fairly harsh environments. They have a symbiotic relationship with bacteria that live in their tissues, between the cells. These bacteria fix nitrogen from the atmosphere, making it available for use by the plant. Gunneras also have a relationship with fungi in the soil, allowing them to absorb phosphates more easily. Both these types of symbiosis mean that they can grow very well on fairly poor soils. Many species are found in bogs; the South African species is always found in or right next to water.

The huge-leaved Gunneras are often grown in botanical and other gardens. In some places they’ve escaped and may be a threat to native plant-life, being able to grow rapidly and grab all the sunlight for themselves with their large leaves.

Just to be funny, there are a number of Gunnera species with quite small leaves, in New Zealand as well as in South America.

Also, a small, weird plant found in South Africa, called the ‘resurrection plant’, Myrothamnus flabellifolius, may be related to the Gunneras. This plant dries out in the dry season or during dry spells, looking brown, dead and shriveled. A little water on it, however, ‘resurrects’ it, as it turns fresh and green again.