Crystals in the leaf litter

Another day, another poke about in the garden.

This dead bramble leaf provided much distraction today. More specifically, it was the tiny grey blobs on the bramble leaf that caught my eye. See 'em?

Once I'd got them under the stereomicroscope, I could see that they were the 'fruit bodies' [sporangia] of a slime mould. So I got my slime mould book out: 'The Myxomycetes of Britain & Ireland' by Bruce Ing. I don't have much experience with slime moulds, but I guessed this one might be a Physarum species...

The sporangia were just stunning to look at under the microscope so I spent a while getting a focus-stacked image of one. I saw that the outer surface [peridium] is covered in frost-like particles.

Focus-stacked image of the peridium. Around 40x magnification.

The round mass of spores, enclosed by the peridium, sits on top of a stout white, slightly furrowed stalk – shown here on one of the sporangia which had neatly broken into cross-section.

Focus-stacked image of a sporangium in cross-section. Around 40x magnification.

You can see here the round flat base to the stalk which anchors the sporangium to the surface it's growing on: the hypothallus. From the tip of the stalk [the columella] tiny threads radiate outwards; these threads form the capillitium: the structure which holds, and assists dispersal of, the spores.

Here are a few of those threads under the microscope.

Section of capillitium. Mounted in water, 400x magnification.

Flicking through Ing's book, the description of Physarum leucopus sounded close to what I was looking at. But it noted also a "close resemblance to Didymium squamulosum".

I dipped into the British Mycological Society Facebook page, to see if previous discussions there would illuminate the difference between these two species... And I found that Steven Murray had commented on a similar-looking collection last year (here) that angular star-shaped crystals are indicative of Didymium.

I scanned across the material I'd prepared under the microscope. And I think I've found what I was looking for.

Star-shaped [stellate] crystal shown with two minutely-warted spores. Mounted in water, 1000x magnification. Focus-stacked image.

Wow! Slime moulds really blow my mind. How do they create crystals out of bits of old bramble? Damned if I know.

I think that makes my collection Didymium squamulosum.

For the record
Date: 13 April 2020
Location: My garden, West Sussex