02 July 2015

Auckland walks: Discovering lichen in Cornwall Park

One of the recent free guided walks around Cornwall Park covered the fascinating topic of lichen, a subject I knew next to nothing about – and still don’t! But I did learn a few interesting snippets from our most knowledgeable guide, Dr Dan Blanchon, a lecturer at Unitec and New Zealand’s only lichenologist.  

The basalt rock of Cornwall Park’s ancient lava flows provides a good environment for lichen so the park is rich in species and plentiful in examples. Lichens actually help to erode the rock they live on but this happens so very slowly that any change to the rock would only be noticeable over hundreds, if not thousands of years. Also, for those of you who have lichen living on their garden trees, the lichen won’t kill the trees – they are, apparently, a sign of the tree’s decline.

Some lichens also live on metal, as you can see on this drainage grate. I thought Dan said this was called the ‘sexy path’ lichen, but perhaps I mis-heard (imagined?) that as I can’t find that name anywhere. I do recall though that he said this particular lichen has a chemical in it that has Viagra-like properties.

Lichens seem to contain quite a diverse range of chemicals, which is one excellent reason for studying them. The lichens themselves use chemicals (and smothering) to try to kill each other – lichen warfare, who knew? Many lichens contains chemicals that are used in dyes – there is, for example, one particular lichen in Thailand that is cultivated specifically for the pretty pinkish purple dye it produces. Some lichens are used in the manufacture of sunscreens as they contain chemicals that protect against UV-B irradiation, and others have anti-fungal and anti-biotic properties. One example of this was the Old Man’s Beard we saw growing on a kauri tree. Several of the different varieties of Old Man’s Beard (Usnea) contain antibiotics, something recognised by indigenous cultures around the world – American Indians used a local variety to bind wounds and, here in New Zealand, Maori also realised the lichen’s special properties, naming it angiangi. (It is still used in a herbal dietary supplement, according to the Kiwi Herbs website.)

Don’t go nibbling on the next lichen you see though. Lichens are mostly indigestible, though reindeer and caribou are known to eat some lichens in the harsh conditions of a northern winter when there is little other food available.

A lichen is a complicated beastie – it is not actually one single organism but rather a fungus living in a symbiotic relationship with a photosynthetic partner, which might be a green alga or a cyanobacterium or both. The fungus is the farmer and the alga and/or bacterium produce/s the food it survives on.

Lichens don’t grow near soil – the nutrients in the soil are too rich and kill the lichen, which is why you don’t usually see lichens growing on the lower parts of walls, as soil nutrients get splashed up on to the wall surface during rainfall. Some lichens are sensitive to the nutrients in urine, so are killed by dogs peeing on walls and the bases of trees. Lichens are also highly sensitive to air pollution so will not grow in polluted places. If you see lots of lichens growing on the trees, rocks, etc., in your area, take it as a sign of clean air.

As you see, no lichens are growing on the lower portion of this wall

If you get the opportunity to look at lichens under a microscope, you’ll be amazed to find they are teeming with life: tiny mites, snails, and weevils are just some of the little creatures you’ll see. And, because of these micro-organisms, lichens are also beneficial to other creatures, like the birds that eat all those little bugs, so try to resist the temptation to kill the lichen you find growing on the rocks and trees around your home and garden.

Although we were told the names of many of the lichens we discovered during our two-hour wander around Cornwall Park, I’m not going to include the names here for fear of wrongly identifying the lichens in my photos. Suffice to say, New Zealand has an exceptionally rich lichen flora, with over 2000 species already named and probably twice that number still to be discovered, categorised and named. Considering the potential benefits to humankind of the chemicals in lichens, I think this country needs more than one lichenologist!

If you want to discover more about these incredible organisms, our guide recommended Allison Knight’s Lichens of New Zealand: An Introductory Illustrated Guide, published by the Botanical Society of Otago and available as a pdf download.  

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