I’ve finally got around to trying to find out more about some of the lichens we found in Ladakh and very interesting it is, too. The easiest to identify turned out to be the gloriously-named ‘elegant sunburst lichen’, Xanthoria elegans.
Xanthoria elegans growing at Chang La pass, Ladakh (5360 m)
This beautiful orange lichen, a relative of the bright yellow Xanthoria parietina which increasingly covers rocks and trees along roadsides in the UK, is found at high latitudes and altitudes, on both acid and basic rocks, all around the world. Whereas X. parietina is flourishing because of its tolerance to sulphur and nitrogen oxides in our atmosphere, X elegans survives a different set of stresses. It is orange because the cells of the algal partner are rich in carotenoids (principally mutatoxanthin), which both act as accessory pigments to make photosynthesis more efficient and protect the cells against damage from too much sunlight. The lichen is darkest in colour when it grows in particularly dry or exposed spots and can survive in extreme desert conditions, where there may be as little as 60 mm of rain a year. Because colonies grow at a slow, constant rate once established, it makes a good candidate for lichenometry, along with our old friend Rhizocarpon (see “The wonderful world of lichens“).
In fact, X. elegans is so resistant to environmental extremes that it is one of a number of organisms which has been studied by scientists interested in species’ potential to survive in space. First of all the spores were tested here on Earth under conditions designed to mimic the vacuum and intense UV radiation in space, and then the lichen was taken into space for a European Space Agency experiment. The lichen was one of 664 biological and biochemical specimens exposed to open space for 18 months, in a tray held outside the International Space Station! X. elegans was the best survivor of all, going into a kind of suspended animation which was quickly reversed once it was back in a more amenable environment and supplied with water. Strangely enough, severe drought is one of the most serious problems faced by organisms in outer space as all water immediately evaporates in the vacuum. Lichens such as X. elegans are amply prepared for this.
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[…] Another thing that seems like a common adaptation, initially, is the red colour of some plants. In Ladakh, we saw Xanthoria lichen using carotenoids to protect its algal cells from excessive visible and UV light at altitudes of 4000-5000 m. It was noticeable that, as we climbed higher, the lichens became darker orange in colour (see More weird and wonderful lichens). […]
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