Oak apples are at their freshest – spongy and sometimes rose-pink – around the time of Oak Apple Day, the 29 May. The day commemorates the Restoration of the Monarchy in Britain on 26 May 1660, when Charles II returned from exile.
The summer generation of the gall wasp Biorhiza pallida, has already emerged. As many as thirty of them live in separate larval chambers in the gall but they’re often joined by parasites and by inquilines: live-in lodgers that don’t attack the resident larvae. The variety of species sharing the gall probably explains the different sizes of the exit holes that they’ve made.
The fertilised females will go on to penetrate the ground and lay their eggs in the roots of oak trees. The larvae usually spend two winters developing underground, each in its own root gall, then emerge early in the year. This early spring generation will all be wingless and all female.
The unfertilised females climb into the branches of the oak and lay numerous eggs at the base of a bud. An oak apple forms from each bud and, as in my photograph, often several of them are clustered together. Males and females develop in separate galls.
These were on a small sessile oak growing by the towpath alongside the Calder & Hebble Navigation, downstream from Horbury Bridge.
These artichoke galls began to form earlier this summer when a female gall wasp Andricus fecundator laid a single egg in each of the terminal buds of this branch of a sessile oak.
Artichoke galls are also known as larch-cone galls or hop galls. The larva develops protected by the overlapping scales.
An adult female will emerge in the spring to lay her unfertilised eggs in the emerging catkins of the oak. The alternate summer generation of male and female gall wasps will emerge from the resulting hairy catkins galls in May or June.
This sessile oak was growing on the embankment of the disused colliery railway which formerly connected Hartley Bank to Addingford, crossing the canal and river en route.
Two species of lichens are thriving on the trunks of trees in the Asda supermarket car park in Dewsbury but nationally, as sulphur dioxide levels decrease, one of them appears to be gaining ground while the other is becoming rarer.
The yellow lichen with the pale-rimmed orange apothecia (the fruiting bodies of the lichen) is Xanthoriapolycarpa, which has spread as levels of sulphur dioxide in the atmosphere decrease.
It’s common on the coast but in urban settings you’ll often find it on twigs, fences and even on painted signs. It can tolerate high levels of nutrients and nitrogen, so it’s common around farms.
What is the source of nutrients or nitrogen here? Do these trees serve as starling roosts or, here in the middle of a car park, does the nitrogen come from vehicle exhausts?
The majority of lichens don’t have common names but the Latin name often includes a succinct description of the species. The genus name Xanthoria means ‘golden yellow’ while the species name polycarpa refers to its many fruiting bodies.
Between the splodges of yellow, a grey-green lichen, Hypogymnia physodes, covers most of the bark. It grows in similar situations to the Xanthoria and tolerates acidic conditions but, nationally, this lichen has declined as air quality has improved. The introduction of smokeless zones and the phasing out of coal-fired power stations has resulted in less sulphur dioxide in the atmosphere and less acid rain.
It’s only in unpolluted sites that this lichen will produce fruiting bodies; there are three or four of them in my photograph above: red-brown discs on short stalks.
This lichen might be thriving here because it’s growing on the bark of a flowering cherry: cherry bark is highly acidic and in a dried, powdered form, has been used for medicinal purposes. The horizontal linear scar, visible amongst the lichens on my photograph, is characteristic of cherry.
The ‘Naked-below Bellows-like’ Lichen
The genus name of this lichen, Hypogymnia, means ‘naked below’ and refers to this lichen having no rootlike growths – rhizinae – on its undersurface.
The species name, physodes, means ‘bellows-like’ and I guess this refers to the lobes along the fringes of the lichen which are shaped like a pair of bellows.
In places the fan-like margins appear to be sprinkled with flour. These are described as farinose soredia. Farinose means ‘flour-like’. The soredia produce powdery granules which contain the fungal and algal cells of the lichen; these become detached and can grow into new lichens.
Both these lichens are foliose, which means they can easily be detached from the surface they are growing on. Other lichens can be crustose and can’t easily be detached or fruticose: bushy.
Lichens, an Illustrated Guide
Coming across these in the Asda car park in Dewsbury gives me a chance to test out my new lichen field guides.
The first one that I reach for is the Field Studies Council’s Guide to common urban lichens 1 (on trees and wood). There aren’t many yellow lichens to choose from, so I soon narrow it down to Xanthoria polycarpa, then, taking a good look at my macro photographs of the grey-green lichen, I immediately pick out Hypogymnia physodes from the chart. I need illustrations; I’m not methodical enough to work my way through a key to identify a species.
There’s a brief summary of key features and habitat in the symbols and the tables included in the FSC guide, but it’s useful, now that I’ve got a name to look it up in an index and to go for the more detailed description and notes on distribution in Lichens, An Illustrated Guide to the British and Irish Species, by Frank S. Dobson, which has just been republished in a revised and updated edition.
There are six FSC guides to lichens in particular habitats – such as churchyards, rocky shores and moorland – so if you’re in one of those habitats it’s easier to have the few dozen of the species you’re most likely to come across to choose from, rather than trying to find it amongst the one thousand plus lichens in Frank Dobson’s book. The two publications work well together.
I already had five field guides on my bookshelves which include a selection of lichens but only one of them, The Observer’s Book of Lichens, briefly mentions the particular Xanthoria that I’ve photographed, but it isn’t illustrated and there isn’t enough of a description to enable me to identify it.
If you’re interested in lichens, I’d say it’s worth investing in these two publications (below). I went for the hardback and I’m pleased to say that it’s been given a binding that stays open when you put it down on the desk, which is so useful when you’re looking something up!
Flaky bark and even flakier tree recognition: I take a closer look at the tree that I photographed on Friday and, although the bark is flaky, it isn’t as flaky as that of London Plane: it’s Horse Chestnut, which probably explains why the bark is so polished; it’s been climbed by generations of conker collectors.
At this time of year, the swelling buds are almost as distinctive at the autumn conker fruits. The bud scales are red-brown and sticky and beneath them are the shield-shaped scars where last year’s leaves were attached.
The lenticels that dot the twigs are raised pores which allow for gaseous exchange.
There’s often a carrion crow on the old felled sweet chestnut trunk near the Lower Lake bridge, feeding on grain that’s been left there and frequently being photographed. You can see in my photograph that it’s stuffed its crop with grain.
A few rooks feeding alongside jackdaws on the turf in Obelisk Park also have full crops, but they are more likely to be feeding on earthworms and insect larvae, such as leather-jackets: the caterpillar-like larvae of the crane fly.
Under a yew near the Menagerie seven grey squirrels have gathered. They’re turning over the leaf litter and stopping to nibble at frequent intervals. One appears to have found half a nut, probably an acorn that it – or another of the squirrels – had hidden during the autumn.
We disturb the adult grey heron yet again. This time it was hoping to be left in peace at the top end of the lake beneath the Cascade Bridge. It takes off, clearing the clapper stones of the Druid’s Bridge with inches to spare.
The flock of fieldfares are still around. Wigeon have left the now completely ice-covered field pool. There’s a pair on the Middle Lake, along with two pairs of gadwall, tufted, the usual mallards and swans and an increasing number of goosanders, some swimming in pairs.
There are more wigeon on the ice-free Upper Lake, which isn’t accessible from the Park.
As we walk along the edge of Top Park Wood, a kestrel wheels from tree to tree ahead of us.
On the northern half of the trunk of an oak by the Lower Lake a coating of powdery green algae shows up in the morning sunlight. It is absent from the sunny south side of the tree so, if you’re trying to do a bit of natural navigating and you’re lost deep in the forest this could help you to orientate yourself.
This is probably Pleurococcus or a very similar-looking species of green algae. Seen through a microscope, Pleurcoccus is a globular single-celled alga with a thick cell wall to help it resist desiccation. The individual cells are slimy and stick together to form the powdery coating.
Green algae contains two kinds of chlorophyll: Chlorophyll A and Chlorophyll B. The two molecules work together; Chlorophyll A absorbs blue-violet and orange-red light while B extends the spectrum by absorbing blue light. The green that we see is the light that doesn’t get absorbed.
There’s a heavy crop of oyster mushroom(above) on some sweet chestnut logs, the entire trunk of a felled tree, which have been left as a habitat in Thornhill Park. Oyster mushrooms are currently £10.80 per kilogram at Sainsbury’s, so there must be hundreds of pounds’ worth here, although some are a bit past their best.
The logs are also sprouting honey fungus(left), which is said to be edible when young.
On the stump itself, the common bracket fungus of dead wood, Trametes versicolor is growing. The brackets are paler around the edges.
This silver birch, down by the canal near the Figure of Three locks, was catching the sun. I’ve added a watercolour filter in Photoshop to bring out the texture of the diamond-shaped scars of its bark. Hopefully, I’ll be getting down to actually painting some watercolours in the new year!
I feel that I can already tell that the days are getting longer and it’s good to think that, in two months time, dogs mercury and lesser celandine will be springing up on the hedgebanks with coltsfoot appearing on disturbed ground.
For the moment though, the only conspicuous flowers are those of hogweed.
Hazel catkins, as yet unopened, are now prominent in the hedgerows.
There was a soft arc of a rainbow over the valley this morning as we set off across the fields via Smithy Brook to Thornhill.
Boxing Day Walk
I’m pleased that over the Christmas period we’ve managed to get out into our local countryside to walk our regular ten thousand steps because a news item in this month’s Healthy Food Magazine reports that researchers at The University of British Columbia have:
“found a link between getting a nature top-up with an increase in general happiness and health during a two-week study. Participants were split into three groups: a control group, a group noting down human-made objects and those documenting nature finds. It was the last group that experienced the biggest boost in self-perceived wellbeing.”
There was me thinking that catching up with my family and eating lots of Christmas cake and mince pies was what had given me a seasonal glow of wellbeing. I should have realised that it was getting my boots muddy and observing rainbows, fungus-covered logs and birch bark.
As the light faded, I drew one of the ash trees at the edge of the wood using a new version of Clip Studio Paint for iPad. For the next few weeks, there’s an opportunity to give it a six month free trial.
It feels so much more direct than using the iPad with a wifi link to the same program running on my main computer and I appreciate the thought that has gone into redesigning the interface to make it more suitable for a tablet.
I started with a pencil drawing then, on a new layer, added a suggestion of colour, finishing with an ink layer for drawing with the G-pen.