Arcyria obvelata at Strumpshaw Fen woodland – June 2025

On the 16th of June we visited the reserve again to check out the slime mould phaneroplasmodium that we saw a couple of days ago. At The Dell we spotted four small slime mould clusters that we thought were Stemonitis. Later on, near The Outpost, we discovered a superb display of the slime mould Arcyria obvelata.

Stemonitis at The Dell…?

It pays to turn over wood on the ground – sometimes there’s a slime mould. Like at The Dell when we revealed four small clusters of what appeared to be Stemonitis primordia.

But the next day it was clear that they were Arcyria obvelata !

The next day…

And four days later…

Arcyria obvelata galore!

After uncovering what we initially thought was Stemonitis at The Dell – only to find the next day it was Arcyria obvelata – we continued on to the trunk near The Outpost, which has been host to a number of different slime moulds this year. It seems to be at the perfect level of decay retaining moisture for longer periods (Stemonitis, Badhamia utricularis and plasmodia).

Arriving at the trunk, we were presented with a superb display of Arcyria obvelata clusters at various stages of development.

The photos below show clusters of primordia – the stage before sporangial elongation.

The next day these primordia had transformed into pale beige worm-like sporangia.

And the day after, the sporotheca were dehiscing and their capillitial spore masses puffing up and elongating.

On the third day, there had been more capillitial elongation and puffing up, and spore dispersal was evident from the cream coloured dusting.

The clusters below were at the sporangial elongation stage.

The next day, the clusters were at slightly different stages of maturity – some showing fawn-coloured tips before transitioning to pale beige.

This eruption of capillitial spore mass of two sporotheca is wonderful!

The plasmodium in the centre of the photo below looks like it has been disturbed producing this malformed structure with a perimeter of struggling sporangia compared to the two clusters directly above.

The next day the the surrounding sporothecae had dehisced and had produced their elongated capillitial spore masses, whereas the malformed cluster had not transformed much from the day before.

So wonderful!