Monday, 31 January 2011

All you have to do is look

Lichens are always described as a fungus and one or more algae (or cyanobacteria) living in symbiosis. The fungus provides structure and anchoring for the partnership and the algae transform sunlight into food via photosynthesis. I'm not so convinced that the partnership is quite as symbiotic as we're led to believe: in a symbiotic relationship, the partners cooperate to mutually benefit each other, but I think the fungus has the upper hand in a lichen for a number of reasons:

1) The methods of reproduction are all either purely fungal (via fungal fruitbodies that produce fungal spores), or are controlled by the fungal partner (broken or ejected fragments of lichen contain the fungus with a convenient bundle of algae already confined, ready for the next specimen).

2) The algae that are found in lichens can happily exist independently of the partnership: the fungal component cannot.

3) The fungal partner benefits from the food produced via photosynthesis which it cannot perform by itself, but what does the alga receive in return, apart from a place to live?

4) The alga can only reproduce within the confines of the lichen body: as the lichen grows, there is more space for the alga to grow.

I rather think the partnership is heavily weighted in favour of the fungal partner. 

This is a specimen of Graphis scripta (so-called because the spore-producing fruitbodies closely resemble handwriting):

Thallus of the lichen Graphis scripta
Notice the shape of the lichen: it is much wider than it is tall, and for a while I wondered why this characteristic shape is the norm for so many of our crustose lichens. The answer is quite simple: in percentage terms, a tree expands in girth much more quickly than it expands in height. The lichen grows at a common rate (perhaps a millimetre per year) in all directions from its starting point, but the bark of the tree expands more quickly horizontally than it does vertically. Over the years the lichen takes on this characteristic shape in response to the growth of the tree.

Here's another example:

Thallus of the lichen Pertusaria hymenea
I have actually been photographing the above specimen for perhaps 8 years now, and it's beginning to show its age: The thallus has been eaten away in a number of areas, most likely by slugs or snails. The bark of the tree has also split on the left, and this has almost split the original lichen into multiple specimens. Finally, Ivy has been growing on the tree and some of its tendrils have been pulled away, taking some of the thallus with them (you can see traces of the Ivy tendrils at the lower edge of the lichen, to the left of centre, looking like a fossil, and in the pale line to the right of the image).

(The dark blotches to the upper right and lower centre are the liverwort Frullania dilatata.)

I took a close-up of a much younger specimen of the Pertusaria, and you can see that it is much more rounded at this stage, but the vertical cracks that will spread it horizontally have started to appear:

I suppose the spaces get filled in with new thallus body as the lichen grows. So here we have a fungus that not only knows how to garden (it cultivates the alga), but has also learned a bit of DIY to plaster over the cracks.

(Click here for an image of the Pertusaria from 2004)

Monday, 17 January 2011


I thought I would take a look at the likely suspects today and found encouraging signs that our wildlife is at least having a try at this early point of the year.

A single Snowdrop was just opening; the rest were still firmly closed.

And a single Lesser Celandine bud had appeared:

The closely-related Ivy-leaved Water Crowfoot has started to come into growth on the muddy entrance to the field:

The jelly fungus Tremella mesenterica, or Witches Butter, appears to grow on dead Gorse branches, but in fact it's parasitic on the almost-invisible crusting fungus Peniophora incarnata, which grows on dead Gorse: 

This stacked dependency is a recurring theme in our wildlife: without the Gorse there would be no Peniophora and without the Peniophora there would be no Mesenterica. When you consider that Gorse is also the specific host for some moths, beetles and other fungi, you begin to see that removal of one species can have a significant impact on the whole series of its dependent species.

I also spotted the Hawthorn associate Tubaria furfuracea:

Award yourself bonus points if you can identify the leaf to the left of the image.

Tuesday, 4 January 2011

Brief seasons

In my previous post I showed an image of the December Moth and mentioned that they had emerged immediately after a thaw. Within 24 hours of the photograph, we were plunged into the coldest spell of weather in over 20 years. I haven't seen a single specimen since - and I have read similar reports from elsewhere, so I suppose their local season was perhaps 48 hours long. That might just explain the urgency with which they seek a mate.

Similarly, I found a few specimens of the Winter Moth over a couple of days:

Winter Moth (male)
Again, their season appears to have been dramatically curtailed this year.

The temperature reached -17 Celsius in the garden, which is by far the lowest I have recorded here. It will be interesting to see how different species are affected by this dip in overwintering temperature: some species overwinter as eggs, some as larvae, others as pupae and some as adults, and it is difficult to predict how a lengthy period of such low temperatures will affect the various alternatives.