Black Fungus

Perithecia of a Rosellinia sp fungus growing on a decaying branch from a birch tree (Betula sp).

I took the following specimen

It yielded these spores (magnification x600, field width 86um):

These are about 21 x 7um which matches the quoted sizes for several of the commonest Rosellinia species in the UK, such as R. aquila (18-22 x 6-8um) and R. mammiformis (17-21 x 6-7um).

I used a razor blade to cut open some of the perithecia.  One of them was filled with milky water and was lined with asci (magnification x60, field width about 860um, reflected light):

In the following close-up you can make out the developing spores in the asci (magnification x150, field width about 344um, reflected light):

First photo and specimen taken in Whiteknights Park, Reading, UK, on 2014-02-02.