Olive Oyster, Sarcomyxa serotina

 

On the wonderful felled Beech I was so pleased to find the Olive Oyster, Sarcomyxa serotina, which some think of as regularly found, but others regard as uncommon in the UK, There are a few records for Kent and for Wales, so not really worth making too much of a fuss about, but definitely a new one for my own life list.

The etymology is Sarco = flesh, myxa = slime, and finally serotina = late, as in appearing late in the year.

Gilled one sided basidiocarps 1 - 4 inches across, with a very short stipe, often tightly packed, and perhaps distorted in shape as a result. Almost invariably on fallen deciduous trees, such as oak, birch and beech. The cap starts off green or an an olive colour with greenish tints, the underside pale cream or tan with perhaps eventual yellowing as the spores develop and start to be released.  The gills are relatively quite crowded, and the flesh feels distinctly and very obviously rubbery. The cap is finely velvety at first, then smooth, and usually slimy when wet. It usually contains some hint of the greenish or olive colours it is named after. At a later stage I think the fruiting bodies tend towards various browns, and then an overall tan colouration, and the colours are generally variable and rather inconsistent, so not always providing a reliable identification. 

One major distinguishing feature of Sarcomyxa, the Olive Oysterling (it is thought there is only the one species currently found in the UK), as opposed to Panellus the true "Oyster" mushrooms genus, is a relative clear distinction between where the gills stop and the stem surface, an arrangement described perhaps as adnate. In Panellus by contrast the gills tend to run on down the short stem or stipe, sometimes called a nub, in a decurrent fashion. 

This is an image of some fresh Olive Oysters from the Beech tree, very like the usual "classic" depiction of them, although not the basidiocarps that I saw first in the tree. You can see here how they get their name, and quite how attractive they look - in their own way of course. 

These were actually the first basidiocarps that I saw - well past their best, but rather more visible at a distance than the fresh ones, probably largely because their brighter colours contrast so clearly with their substrates and the surroundings.

I twisted one of these fruiting bodies around to show the gilled underside:

And here is a view of some other fruiting bodies at an earlier, intermediate stage I think, with the two uppersides showing some nice colour variation. Note the clear yellow spore-staining on the underside of the other fruiting body near the stipe, quite characteristic of the species.