Sunburst Lichen

The Island’s winter landscape is mostly monochrome, making the occasional burst of colour all that more beautiful. One of my favourite bright spots is the aptly-named Maritime Sunburst Lichen (Xanthoria parietina).

Lichens are interesting in many ways, including how they survive our coldest months. Most living things go to great lengths to protect themselves from drying out or freezing: two major (and usually lethal) side effects of winter. That’s why PEI’s trees, plants, fungi and even some animals go dormant. Lichens can’t escape the elements and have instead adapted to tolerate some of the most extreme conditions on Earth – and beyond!

Unlike most plants and animals, lichens have no way to prevent water loss; their water content rises and falls with their surroundings (the term for this is ‘poikilohydric’). This is an advantage in sub-zero conditions: the less water you have, the less likely you are to develop cell-destroying ice crystals. Desiccated lichens can survive for years, bouncing back as soon as water is added.

Lichens can also survive freezing. Ice needs something solid to kickstart its formation: dust, food particles, bacteria, or other contaminants for example. That’s why you can supercool pure water to well below 0^oC and have it remain liquid: there are no nucleation sites for ice to start. Lichens provide nucleation sites outside their cells, so any ice that does form will be there rather than inside the cells where it would kill them.

This remarkable ability to survive desiccation and freezing has led scientists to test lichens in space. Xanthoria elegans – a close relative of the lichen shown here – was exposed to conditions outside the International Space Station for 18 months. Despite experiencing unfiltered solar and ultraviolet radiation, cosmic radiation, the vacuum of space, and extreme variations in temperature, more than 70% of the lichens survived and returned to normal once back on Earth.

The Maritime Sunburst Lichen is common across the Island, most often found growing on Poplar and Elm trees (Populus and Ulmus species) or on stone. It’s easy to spot even from a distance at this time of year, so keep your eyes open for this remarkable part of PEI Untamed!