Wednesday, January 7, 2015

Gall Update

by Bruce McDonald

In the December 2013 newsletter we published an introduction to galls, including those we had encountered on some of our field trips. This is an update on some that we have come across more recently.

This slightly cashew-shaped gall (above) is Taphrina pruni and it has altered what started out as a sloe. It is caused by a fungus and the common name of Pocket Plum derives from the action of the fungus which destroys the stone and seed leaving an indentation. These were abundant in 2014 along the stretch of sea-wall from the Britannia Inn at Llanmadoc on Gower and down towards Whiteford Point around Grid Ref SS 4466/9416. The gall starts off greenish and ends up shrivelled and blackish - it is closely related to Taphrina alni, the tongue-like gall on alder cones (see last newsletter for photo). It has been a good year for sloes and despite extensive foraging to produce Sloe Jelly, this was the only location at which I noticed it. The sloes were spotted in June - a few months later the sea-wall was breached and the footpath closed.

The next one is Andricus grossulariae (above), one of the Oak Tree's many galls, especially Turkey Oaks. It is similar in appearance to the Hedgehog Gall or Andricus lucidus but the latter has each spine tipped with a small knob. With grossulariae the projections are flatter. This was spotted at RHS Wisley and was first found in the British Isles in 2000. It is spreading rapidly and has been found as far north as Cheshire, although SEWBReC does not have it recorded on their public database. One to look out for, as it should not be long before it is found in South Wales.
On Esher Common was a pear tree dripping with fruit but it also sported the gall seen above. This has the instantly-memorable name of Gymnosprangium sabinae although European Pear Rust is probably easier to cope with. This rust fungus was once confined to mainland Europe and seldom seen in the UK, but is now becoming more common. It infects both Pear and Juniper and needs both to complete its life-cycle. It is a biotroph with the spores from the pear unable to re-infect the pear directly but needing to find a juniper through wind-born dispersal. Having infected the stems of juniper the spores from this can then seek out a pear to infect.
The final one was found on the Community Orchard at Wenvoe, which we visited in early September. Galls on grasses are not easy to identify and Redfern and Shirley in their key ID guide British Plant Galls comment: “Galls on grasses are not well known; they are difficult to find and their host associations are often unknown”. Having said that, the photo above shows a gall which tends to fit the description, “stalks of panicle and of individual spikelets shortened, spikelets broad and bunched together, their parts thickened, green and leaflike”. So Aceria tenuis caused by a mite is a potential candidate.
Photos by Bruce McDonald





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