Craterium minutum ? slime mould at Strumpshaw Fen – December 2025

23rd December 2025

Serendipity again!

While I was taking photos of the Heterotrichia ferruginea sporangia, the daughter happened to kick about some of the oak leaves around the high stump and she spotted Craterium minutum — another first for us 🤩

Or at least, that’s what I thought — writing up this post, examining the photos and consulting various references, I'm not entirely certain... 🤔

In the photo below the sporangia are growing along the oak leaf margin.

And below they are growing on the leaf surface.

Despite their maturing form, these yellow-orange sporangia are still fairly juvenile — the sporothecae have that youthful luminosity about them.

You can see the emergence of the cup and the distinct paler circular peridial lid.

This is a wonderful photo below — three of the sporothecae have hemispherical droplets of water on the lids.

The photo below shows some mature forms with exposed inner cups.

The sporangia on this leaf below are still fairly juvenile.

While these ones below are more mature — the colours are more muted.

I was perplexed by the sporangia below with their light deep-olive tops to the sporangial cups — and the middle-left sporangia appear to have the remnants of a pale lid, but these darker tops are still lid-like rather than the exposed spore mass.

The photos below are the younger sporangia from the other leaf.

The following two photos show (at the back) what I contend are more mature forms from the same group.

A Crisis of Identification!

As I was wrapping up the draft of this post, I had a crisis of identification. I couldn't help think that I was looking at two different slime mould species.

I took a deeper dive checking out Taxonomic Keys and Plates from The Myxomycetes (George W. Martin and Constantine J. Alexopoulos), Bruce Ing's UK Identification Handbook, A Handbook of Slime Moulds (Stephenson & Stempen), and searching for research-grade information on Craterium.

There's so much variability with slime moulds even within the same species, and of course as they develop from juvenile to mature forms.

However, the yellow-orange sporangia do appear distinct from the muted sporangia. They range from juvenile to mature within what I think is a distinct morphology and colour spectrum than the muted sporangia. And the sporotheca appear to attenuate more smoothly into the stalk, whereas with the muted sporangia, the base of the sporotheca, in my view, meets the stalk far more abruptly.

So... I considered whether the yellow-orange sporangia could be Craterium aureum — on the basis of Ing in his handbook describing Craterium aureum as:

...sporangia... bright yellow

...the colour separates it from other members of the genus...

And whether the muted sporangia were Craterium brunneum...? But then Craterium brunneum is currently a synonym of Craterium minutum !

Or they were all Craterium minutum and it goes to show the large variability within a single species.

As I was putting my gear away, the eagle-eyed daughter spotted something different on another leaf — not only were there some Craterium sporangia but also, clearly, plasmodium. Surely it must be Craterium plasmodium!

You can see the dark orange-yellow plasmodium on the right of the leave. The plasmodial blebs will develop into individual sporangia, but that long worm-like plasmodiocarp form — just super 🤯