Rock Tripe on Quinag

December 24th 2019

Rock Tripe on Quinag

On the south-eastern slopes of Quinag, just north of Creag Sgiathaig, there is a small dumbbell-shaped lochan, about 100m long (NC223258).  It occupies a hollow at about 230m altitude and appears to have no outlet.  I had last visited it on survey in September 1993, when I had noted a very impressive lichen, growing on angular quartzite boulders around its waterline.

On 16th November 2019, Gwen Richards and I thought we might revisit the site to see if the lichen was still present.  We parked high on the south side of ‘Skiag’, crossed the burn and made our way south-west across somewhat slippery wet heath patterned with ice.  Coffee was taken on a jagged rib of quartzite, stretching right up the hill to the summit of Spidean Coinich (photo 1), just as the lochan came into view (photo 2).

I was at first pessimistic about our chances, since the lochan was iced over (photo 3), but as we dropped down to its margins, Gwen spotted it, in quantity, on partially submerged boulders, both above and below the ice (photo 4).  It was also locally abundant on vertical faces around the edges of the lochan (photo 5).

It is Lasallia pustulata, the largest British member of a group known as ‘Rock Tripe’.  These are rock-hugging foliose lichens anchored to the substrate by a single central holdfast (hence the generic name of most of them, Umbilicaria).  Individual thalli of this species grow to over 5cm; they are grey-brown and covered in ‘blisters’, looking a bit like a seriously over-cooked omelette (photo 6).  The ‘blisters’ develop a fuzz of dark brown coralloid isidia (photo 7), adding to the exotic impression.

L. pustulata was once used in dyeing, and even as a ‘survival food’, but probably not hereabouts, since this is the only known site for this impressive lichen in Assynt (although it is recorded from the hills south of Durness). Further south it occurs, commonly in places, on the surface of nutrient-rich rocks, especially in rain-tracks ‘where the wash-down water has percolated through soil’. This doesn’t seem to square with its habitat locally, on what I take to be mineral-poor quartzite around the edges of this lochan, and a pH reading of the water might be enlightening.  I should be interested to hear from anyone who comes across it elsewhere.

We left the lochan after lunch, as the light began to fade, with good views of the snow-covered hills to the east (photo 8).  Back home, I thought I would check the meaning of sgiathaig, from which the crag, burn, bridge and hill on the road north (the latter two in the anglicized form skiag) take their name.  It is the genitive form of a diminutive of sgiath, and appears to relate to a small outlier or ‘wing’ jutting out from a larger hill, which fits.

Ian M. Evans

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