Saturday, March 28, 2009

Candlesnuff fungus Xylaria hypoxylon

I am an amateur naturalist trying to discover everything that lives in my garden.
Chomping its way through a fallen twig, photo 1 shows a collection of the 'candle wick-like' fruiting bodies of the Candlesnuff fugus Xylaria hypoxylon.

This fungus is very common here in the UK. Scan piles of logs or fallen branches and you're likely to spot it on almost any country walk.

In common with the holly leaf fungus I blogged recently, and the morel before that, X.hypoxylon is a member of the ascomycetae - a huge collection (phylum) of fungi that 'grow' their spores inside microscopic tubes called asci.

In the case of X. hypoxylon a couple of hunded asci are, in turn, packaged into a structure called a perithecium - basically a small 'pimple' with a hole in the top through which spores, once liberated from an ascus, escape. There's an excellent cross sectional microscope photograph of a perithecium of one on the mycolog site (it's a big webpage - the photo's about half way down).

To the eye, the perithecia of X.hypoxylon appear as tiny black pimples on the surface of the white 'candle wicks'. You can see some in photo 2. (Perithecia are common features of lichens also (see my post here).) Over time, the surface tends to become increasingly covered with these pimples (compare Photo 1 with Photo 3 taken about two weeks later) until finally the 'wick' ('compound ascoma') appears quite black. The resulting 'charred' look gives the name pyrenomycetes (from the Greek 'pyr' = fire) to the class of mushrooms of which X.hypoxylon is a member.

The definitive web site on the pyrenomycota is that of by J.D. Rodgers.

In fact the life cycle of X.hypoxylon is a little complex. The spores liberated by the pimply black perithecia are the result of sexual reproduction. X. hypoxylon is also able to reproduce asexually via so-called 'condiospores' however. These conidiospores give the fungus its white powdery appearance in photo 1.

Seen under the microscope, the sexual spores of different species of mushroom show characterisitic differences in size and shape (a helpful aid when trying to identify a mushroom - see my previous posting). I read on Michael Kuo's site however, that conidiospores from different fungi all look basically the same. Why nature has chosen to distinguish sexual and asexual spores in this fashion I can't imagine. Can anyone comment?

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