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www.thevillagenews.co.za
2 September 2020
MY ENVIRONMENT
Lichen – a unique fungal organism By Dr Anina Lee
O
n a beautiful early-spring day in Hermanus, I took a stroll on the famous Cliff Path. Being of a certain age and with more metal in my hips than I care to admit, I sat down on a convenient bench and tried a little whale-spotting. Since there did not appear to be cetaceans of any kind within view, my gaze drifted to the rocks forming the cliff along which the path meanders. What fantastic shapes and colours meet the eye! The red lichens on many of the rocks are particularly noticeable. Why are they red and what exactly are lichens anyway? To start, lichen is pronounced ‘liken’. Some people say lichen to rhyme with ‘kitchen’, but we don't really do that in South Africa. What are lichens? A lichen, or lichenised fungus, is actually two organisms functioning as a single, stable unit. Lichens are composed of a fungus, living in a close symbiotic relationship with an alga or a cyanobacterium. What are the benefits of this
intimate relationship? Fungi are incapable of photosynthesis because they lack the green pigment, chlorophyll. In other words, fungi cannot harvest light energy from the sun and generate their own food in the form of carbohydrates. Instead, they need to find an outside source of food or, in the case of lichens, a partner to make the food and share it with them.
Lichens come in many forms and colours. These are primarily dictated by what other organism the many different fungal species choose to form a relationship with – algae or cyanobacteria – and on the environment in which it grows.
In contrast, algae and cyanobacteria can photosynthesise, just like plants. The chloroplast with which plants make food for themselves is actually a cyanobacterium living within the plant's cells.
Is the relationship monogamous? Usually, once a lichen association has been established, the fungal partner does not switch partners and they remain together, forever. However, there is an exception.
So when a fungus links up with an alga (usually a green alga) or a cyanobacterium, to form lichen, it is providing itself with constant access to a source of nourishment. One can think of the fungus ‘farming’ the alga or cyanobacterium for food. In return, the algae and cyanobacteria secure a protected environment. The fungus filaments almost ‘embrace’ the tiny food-producing partners and keep them safe from the elements.
One particular kind of fungus can form separate lichens with different photosynthetic organisms. In this specific case the fungus associates with a cyanobacterium in shady, humid conditions to create a small, shrub-like lichen. However, in drier or more exposed situations, the fungus associates instead with green algae to form large, flat lobes.
The significant advantage of this interdependent relationship is that, in the form of lichens, fungi, algae, and cyanobacteria can live in environments that they could not live in separately. The sun-drenched, windblown and salt-sprayed rocks on the Cliff Path are good examples of such an inhospitable environment.
A particular fungus can hook up with either one or the other – or both! But hook up it must; it cannot survive on its own.
When conditions change over time, you may see some individuals starting as cyanobacterial lichens and then suddenly building green lobes by associating with green algae. So, although lichen relationships are obligatory, it appears that the fungus partner is not above ditching one partner for another as circumstances dictate. They are, in fact, not always together forever.
WCC is delighted to resume their walks in nature as from September, kicking off with a repeat of the popular geotrail with David Mourant on Tuesday 8 September at 17:00. Walk from the western portion of the Hermanus Cliff Path to look at the amazing rocks and hear the explanation of how they were formed. Booking is essential as groups will be limited to 10 (with masks). Adults pay R120, children are free. For more information and to book, send an email to anina.wcc@gmail.com.
TOP: Red lichen on the sandstone cliffs along the Hermanus Cliff Path. PHOTO: Anina Lee ABOVE LEFT & RIGHT: Lichens come in many forms and colours. PHOTOS: Science Minus Details & The Economist
The next webinar in Whale Coast Conservation’s series Inspiring Stories of our Natural World is a Zoom chat with Bernard Coetzee about Light Pollution: the dark side of keeping the lights on, on Thursday 3 September at 18:00. Register at https://us02web.zoom.us/webinar/ register/9015926545433/WN_2Aiy4OMwRPS1I9iioP__WQ
