Hi Mirek.
Interesting but the specimens seem immature, so I think better waiting for a spore print to evaluate correctly the ornamentation.

Perhaps these Peziza's grew near to a plant Lathraea sp.? We find very similar (macrosopically) specimens near to it, but so far we cannot identify them. Unfortinately i don't have microscopic images of it at now.

Hello
Nicolas, that's why I grow a fruiting body :)
I left a few in the forest!

Sergey, thank you for reminding us about Lathraea sp. :)
I was supposed to write about it to Nicolas on the occasion of sending Peziza cf. howsei. I forgot, but since you reminded me, I take this opportunity:
Nicolas, the collections that I sent you and marked, Puszcza Knyszynska - Czolnowo, grew right next to Lathraea sp.
However, this is not the same genre that I present in this thread! The ornamentation of those is completely different.

Mirek

Hi
The fruiting bodies are already fully ripe. Further breeding threatens to spoil.
I visited the fruiting area again and took fresh fruiting bodies as well.
I did a spores print.
However, I come to the conclusion that it is some kind of albinistic form of P. michelli. All the features fit this genre perfectly. The only thing that is missing is the yellow pigment that colors the outer surface. Some of the spores do have somewhat unusual embellishments on the poles. However, compared to the total number of spores, these are very small. Therefore, I cannot consider it a permanent feature. Most of the spores have an ornamentation typical of P. michelii. In this case, only because of the lack of the typical coloration, I can consider it Peziza cf. michelii.
Of course, I have fruiting bodies and if someone is interested in making a sequence and comparing with P. michelii, I would like to share the fruiting bodies.
I would like to thank everyone for participating in the discussion.
I present a few comparative photos of P. michelii that are present in mass in this area and photos of free spores.
Mirek