Oaks and Acorns

 For the first time, I have noticed plenty of acorns on the oaks trees that I have seen alongside the Calder on the Wildcat Trail, and on a walk on Kinrara Estate (near Aviemore).  Thirty years ago, my daughter wanted an oak tree for her birthday and we looked in vain for some local acorns in the woods at Kincraig but failed to find any that year. We bought a sapling and it is still growing in the garden - and it is her birthday today...

Oaks at Kinrara

There are two kinds of common oaks (there are actually lots of kinds of oak but let's keep it simple!) called the English Oak (Quercus robur) and the Sessile Oak (Quercus petraea).  The latter is more common in the North.  The word "sessile" means seated and when used about a plant it means that there is no stalk or a very short one.  Confusingly, the sessile part of the name  in Sessile Oak does not refer to the leaves, but to the acorns - it has acorns that sit on the twig, but leaves that have a stalk. Whereas the English Oak has acorns with a stalk and the leaves are sessile! I must admit that I find it hard to judge between them from that characteristic. Perhaps an easier way is to look at the shape of the leaves. The Sessile Oak has wavy lobes whereas the English Oak leaves are a bit irregular. I think most of what I see is the Sessile Oak but apparently there is quite a bit of variation with the leaves like one sort and the acorns like the other! So maybe is it not surprising that I get confused. However, they are lovely trees to look at, whatever their name.

The bark on the thick trunks was quite furrowed and when I went for a closer look, there were greener patches with tiny black dots.

The furrowed bark (with a hand for scale!)

The little black dots turned out to have tiny stalks, like little nails.

This is not a fungus but a pinhead lichen called Calicium viride  which is common on oaks.  It was the first time I have found it. 

 I also found a dead leaf with a white "pearl" on it. This is probably a gall caused by an insect such as an oak gall wasp and the larva develops inside and makes the tree grow these strange structures.

I assumed it was long dead and cut it open - but there was a larva inside (oops).

There is another gall called the Oak Apple Gall which is a bigger brown sphere, and was used in the past to make black ink that was used on medieval manuscripts.  There is a great video by the British Library showing how it is made here.