Sunday, January 14, 2007

Cola nut galls (Andricus lignicola)

In a scrubby field in St Leonards-on-Sea, East Sussex I found these cola nut galls (Andricus lignicola) yesterday growing on some young oak trees. The trees were most probably the hybrid (Quercus x rosacea) between pedunculate oak (Quercus robur) and sessile oak (Quercus petraea), not that I think this is of any significance so far as the galls are concerned.

They are caused by a small wasp and chemicals injected by the female at egg-laying time induce the galls to form, thus providing food for the larvae. The cola nut is a plant from tropical Africa and there is only a very superficial resemblance between it and these galls.

Although described as widespread and common, I have been unable to find any earlier Sussex records and, though seemingly not so frequent as the marble gall, I am sure it is overlooked rather than rare.

Tuesday, January 02, 2007

Wall screw-moss (Tortula muralis) in Hastings

I came across this small desert on top of the wall of the bridge that carries Linton Road across Braybrooke Terrace (where the cars below are parked) in Hastings today.

I have watched plants like this colonise bare stone. Often they start as the tiniest pieces along a seam or crack that retains a little more water than areas nearby, then spread out over a few years to form small cushions. Eventually they may join up and make a thin layer of soil where vascular plants can get a foothold and in no time at all you have a forest.

The cushions even at the stage they are at in the picture are often well populated with fauna such as springtails, nematodes, black fungus gnat larvae and the larvae of the parthenogenetic midge Bryophaenocladius furcatus. All these must be able to withstand long periods of desiccation when the moss cushions dry up in summer.

I have been reading Animate Earth by Stephan Harding (2006) and the following passage on life during interglacial periods seemed to be illustrated by these mosses: "Plants grow well in the new high carbon dioxide atmosphere. They send their roots deep in search of nutrients, cracking open rocks with sheer brute force and with the subtle but relentless dissolving powers of their acidic chemical exudations. One can almost hear the gentle grinding noise of the increased weathering as plants all over the planet pummel and pulverize the rock, releasing nutrients on a scale unknown during the time of ice. Myriads of phosphorus, iron, silicon, calcium atoms are captured by plant roots to be sucked up into the growing green biosphere which, in its heedles growth, draws out more and more carbon dioxide from the atmosphere."