Lepraria incana - Dust Lichen

 Learn your Lichens 8

Learn your Lichens Series
1. Arthonia radiata

2. Caloplaca flavovirescens

3. Acrocordia conoidea

4. Squamarina cartilaginea

5. Xanthoria parietina

6. Lecanora gangaleoides
7. Physcia tenella

8. Lepraria incana

The word "Dust" is useful for describing the genus Lepraria. The lichens have no structure and a closer close up reveals... Dust.
Well, fluffy granules.

Leparia means "Scurvy"
incana means "White, hoary"

Our Townhead area of Settle gave yet another lichen to this website series.. On Wednesday Ilona Warham said "Come and see this lichen - it grows in deep shade in crevices in our garden wall - yet it can look ever so bright"

It can sometimes be seen in the distance growing in big very pale blue green -white patches patches on the shady side on mossy tree trunks...  I need to find some pics near Settle..

I took a photo of the  south west facing wall at the edge of their garden. It was built into the hillside 30 or 40 years ago - so the lichens must have grown since then. Ignore Arrows 3, and 4 - Concentrate on the ledge just below arrow 1

The Lepraria incana has been increasing on this wall over the past few years, I was told. 

The Lepraria is bluish greyish green and is growing on the moss and in the crevices

Arrow 2 points to this crevice

When I put my camera close and used the flash you can see there is lots of Lepraria inside.

Lepraria incana in white under UV light.

It is very tolerant to sulphur dioxide pollution.

I first learnt about Lepraria incana when teaching at Malham Tarn in 1979 . The frame of the old coalhouse door at the Field Centre is made of sandstone, whereas the rest of the wall is Limestone. Oliver Gilbert describes it in his paper in 1963 on Malham Tarn House.

The pale powdery Lepraria grows on the sandstone, whereas the bright orange alga Trentepohlia grows on the limestone -- but there is overlap. Click on the article from the paper about Malham Tarn House - Its architecture and lichens by Raistrick and Gilbert in 1963

The wall faces north so is shaded all day, and it is the coal house so the wall is not heated by the building.

We are looking at the wall near the coalhouse in this picture here - the coal house is just off to the right, but you can see a white patch on the gatepost  wall which is Lepraria. (I think - need to go up and double check) - Then I'll photo the "coal house door" too. It looks fairly similar, thoough the wall was drastically repaired/repointed/plants removed 10-20 years ago.

Other plants with the name incana:

Alnus incana - grey alder
Matthiola incana - Hoary stock
Draba incana - Hoary Whitlowgrass or Twisted Whitlowgrass - a rare white crucifer that is found in our area (limestone/mountains)