I suspect I am dealing with Sclerotinia binucleata here, but based on the size of the apethecia, I do not rule out sclerotiorum.
Binucleata was already found on the opposite side of the Rivierbeek in the same forest in March 2024. However, at that time, the apothecia appeared to be significantly larger.
Can my data dispel the doubt?

Macroscopic:
° apothecia: cup-shaped; diameter max up to 16 mm; fawn-colored to dark rust-brown; darkening towards the stalk; weakly hygrophanous
° stalk: dark brown above ground; black below ground; diameter up to 1.5 mm; maximum measured length 53 mm.
° sclerotium: small, up to 5 mm; thin-walled; black; contents white, dry and cottony, not gelatinous.

Microscopic:
° close to the ectal excipulum lies a zone with relatively straight, elongated cells parallel to the outer wall.
° no reactions in the excipulum to Melzer or Lugol
° contents asci (not the spores) dextrinoid in Melzer
° crystals in (on?) the ectal excipulum present in the zone around the stalk attachment
° spores: clearly binucleate; measurement from sporee and in water: (12.1) 12.3 - 14.6 (15.4) × (6.3) 6.5 - 7.1 (7.3) µm
Q = (1.8) 1.81 - 2.2 (2.3) ; N=45
Me = 13.4 × 6.8 µm ; Qe = 2

Many thx in advance,
William

Hans-Otto Baral, 24-03-2026 20:48

Re : Sclerotinia binucleata?

I see no doubt that this is binucleata. In my excel on the features of Sclerotinia, S. sclerotiorum has apos usually below 10 mm, often only 2-5 mm. But indeed there are some samples with larger apos. The largest was 6-16 mm diam. and in association with Symphytum. The stipe length is S. sclerotiorum was mostly up to 20 or shorter, rarely 40 as an exception.

The IKI reaction of the excipulum varies in both species.

Surely this is not a very clear delimitation, but the available DNA data easily permit to identify.

Sequenced finds of S. binuc. had apos of 5.5-15 mm but also 8-23 mm.

I have collection data for Waardamme from 21.3.2024 with R. ficaria, as  S. sclerotiorum, with up to 10 mm diam. The binucleata you mention was from the same day, with apos 8-24(-32). 

The microdata of the small ones are poor, however.

Sequenced specimens of S. sclerotiorum with data are poor, I see only one: Here the apos are 4-7 mm diam and the stipe 6-13 x 0.7-1 mm.

If you could measure the whole range? smallest apos and thinnest and shortest stipe? I measure the stipe width not only above but also at the base. Sequenced binucleata stipes were always min. 1 mm thick.

Zotto