Cribraria argillacea (likely) at Strumpshaw Fen – September 2025

Near Basecamp

7th September 2025

At the Basecamp loop some stunning, immature, gregarious slime mould sporangia!

These translucent, blue-grey sporotheca are utterly wonderful.

But what species? The daughter insists that we had already provisionally ID’d these sporangia as likley Cribraria argillacea, yet I ended up on a frustrating journey, trawling through Bruce Ing’s handbook for mention of blue-grey sporotheca 😭

Because – for Cribraria argillacea – Ing’s description does not entirely fit what we found.

Two hours later, returning to the reserve reception, the sporothecae had lost their jewel-like quality becoming more opaque – some had a deep olive hue.

In the light some of the sporothecae had an iridescence to them.

The next day (8th September) the sporangia had matured – the sporothecae had turned to matt black-grey and pale mouse-grey. The pale mouse-grey sporothecae had darker mouse-grey calyculi (cups).

But interestingly, amongst the maturing sporangia was glistening, metallic dark bluish grey plasmodium consolidating into individual sporangial forms.

After The Outpost

7th September 2025

Following the wonderful sporangia at the Basecamp loop, after The Outpost, I found some groups of glistening metallic blue-grey plasmodia consolidating into crowded irregular globose sporangial forms. These could also be Cribraria argillacea.

Also on the downed trunk were some smaller groups of crowded, spherical sporangia – almost certainly more developed forms of the sporangial forms above. I wasn’t able to determine if these more developed forms were stalked.

The next day (8th September) they had matured to a colour similar to the sporangia we found at the Basecamp loop.

At the time, the differing morphologies between the two finds led me to think that the slime moulds at the two locations were not the same species – the individual, stalked forms at the Basecamp loop were fundamentally different from the sessile, crowded forms that I found after The Outpost. It wasn’t until late December, when the daughter and I found Heterotrichia ferruginea sporulating simultaneously at our Norwich allotment and at Strumpshaw Fen – two sites 15 kilometres apart – that we realised that weather conditions might trigger mass sporulation of a species across an area.

If the same weather conditions could synchronise the sporulation of Heterotrichia ferruginea across the county, then it shouldn’t have surprised us to find Cribraria argillacea across the reserve woodland on the same day. Indeed, we have seen this with other slime mould species at the reserve, but it was the simultaneous sighting of Heterotrichia ferruginea that brought into focus the idea of synchronised mass sporulation. It’s been frustrating, but from what I have been able to gather from the internet – the morphology of Cribraria argillacea can vary very noticeably!