Friday 16th January, 2009

English oak: galls, lichen and fungi

By Ash

What is a gall? The British Plant Gall Society’s site has a good definition from Redfern & Shirley’s British Plant Galls:

A gall is an abnormal growth produced by a plant or other host under the influence of another organism. It involves enlargement and/or proliferation of host cells, and provides both shelter and food or nutrients for the invading organism.

British oaks are particularly rich in galls. Here is just a tiny sample.

A pair of oak marble galls (one not fully developed) caused by asexual Andricus kollari larvae. A. kollari is a member of the family Cynipidae, “whose members are of special interest because most of them induce gall formation on plants and many of them display a marked alteration between sexual and parthenogenetic generations. They are called gall wasps… Most of the European species occur on oaks, although some species attack roses and certain herbaceous plants. There are about 90 British species.” - from Chinery’s Insects of Britain & Northern Europe (Collins Field Guide, 1993). This page at hedgerowmobile.com details the life-cycle of A. kollari and has good photos of the wasps and larvae with cross-sections of the gall.

A pair of artichoke galls caused by asexual Andricus fecundator larvae. Another gall wasp, A. fecundator is closely related to A. kollari. I’ve known about marble galls since I was a kid, but my first encounter with an artichoke gall came recently, in September 2007, on a university field trip to Kintyre. How did I ever miss them? hedgerowmobile.com has an A. fecundator page too.

An unknown gall. Perhaps a partially formed marble gall?

An unknown bud gall. If you recognise this gall and can ID the causal agent, please leave a comment.

Enough galls; how about some fungi? This weirdness has taken over the underside of this branch. The top side is covered with leprose lichen.

More leprose lichen. Notice how it only grows on the right side of the branch. There must be a favourable microclimate there, perhaps because of sunlight or exposure.

Another lichen; this one is fruitcose. As for what species it is… I wish I could tell you.

The subjects of all those photographs were found on this one English or pedunculate oak (Quercus robur). Even though it has split in two, both halves continue to grow; in fact, the large branch that goes off to the right is impressively long.

One more thing! A reminder about the next edition of the Festival of the Trees, which treeblog will be hosting. Please submit your blog posts, photographs, poetry, works of art, articles, news pieces, bark rubbings and anything else tree-related to mail [at] treeblog [dot] co [dot] uk, making sure that Festival of the Trees or FOTT is contained in the subject header. Alternatively, you can use the online submission form at blogcarnival.com. You do not need to be the author or artist of the content you submit. Although there is no theme this month, it would make my day if you submit something pertaining to a particular favourite tree of yours! The deadline for submissions is the 30th of January, so that leaves you a fortnight to get them in. Get to it!

tags: fungi + galls + lichen + oak + photos

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