Strange growth on Oak

[JennyS]

This is something I've never noticed before on Oak and I wondered if anyone could tell me what it is? There were oak galls on one tree but these growths were quite abundant on several trees.



Jenny

[ChrisR]

It looks like an Artichoke Gall - made by a cynipid wasp called Andricus fecundator

[Lancashire Lad]

Hi Jenny,

It looks like Oak Hop/Artichoke Gall - Andricus fecundator.

Regards,
Mike.

EDIT - Just spotted ChrisR had posted whilst I was typing (slowly!).

[JennyS]

Thanks folks, that was fast!

Now to really show my ignorance, what is it classed as?

[Lancashire Lad]

Not exactly sure what you mean Jenny, but it's just a plant gall, loosely defined as - "an abnormal growth on plants caused by other organisms", in this case, an insect.

Regards,
Mike.

[JennyS]

Thanks Mike, its just that I'd been leafing through the 'Rusts, smuts, mildews and gall-inducers' section of Collins Guide to Mushrooms and Toadstools which is why I'd wondered (hence apologies for ignorance) if that meant galls were included.

[Lancashire Lad]

Originally Posted by JennyS

Thanks Mike, its just that I'd been leafing through the 'Rusts, smuts, mildews and gall-inducers' section of Collins Guide to Mushrooms and Toadstools which is why I'd wondered (hence apologies for ignorance) if that meant galls were included.

Ah - I see what you mean.

Some plant galls (such as Taphrina betulus on Birch) are caused by parasitic fungus, but in the case of Andricus fecundator, the gall is caused by an insect, so wouldn't be found in the Collins Mushrooms Guide.

As well as fungi and insects, galls can also be caused by mites, bacteria & viruses. (And probably other things as well ).

There's a nice FSC guide at about £2.50 if you're interested, and also some more information here: -
Galls Page 1
Galls Page 2

Regards,
Mike.

[JennyS]

Funny but I've never really looked closely at them, this one caught my attention as I knew I hadn't seen it before. Is it quite common?

[ChrisR]

Pretty common but I suppose when they are green they are harder to see and one might be forgiven for thinking it was just a big leaf bud Oak galls are very numerous and most trees will have at least 1 species so it can make for quite a fun addition to your repertoire

EDIT: Just noticed your location - not sure about their distribution in Ireland

[JennyS]

My repertoire has got a bit stuck on lichen at the moment!