On the 2nd of February 2026, I found a 10 cm long twig covered with perithecia with strikingly long necks (up to 1.5 mm) on Hedera helix. Under the bark was a black stroma.
Perithecia were spherical, up to 440 µm in diameter, black with straight or slightly curved thread-like ostioles up to 1500 µm in length.
Inside the perithecia was a gelatinous content consisting of hundreds of asci (average: 48 x 6.8 µm; Q= 7.2).
Spores (average 12 x 3.1 µm Q = 3.9), usually with septum in the centre and two large droplets in each half.
The reaction of the apical ring in Lugol's or Baral's solution is difficult to determine; Congo red not tested.
While viewing one of the preparations, I found ellipsoidal light brown conidia with the following dimensions: 3.6 x 2.1 µm, no conidiophores found.
Using the key mentioned in the publication by L.E. Wehmeyer(*), I identify the ascomata as D. medusaea (according to Mycobank: current name D. rudis).
This raises two questions:

1. Is Diaporthe rudis correct?
2. Is there a connection with the conidia?

Many thanks in advance,

François Bartholomeeusen

(*)Wehmeyer, L.E. (1933) The British species of the genus Diaporthe Nits. and its segregates. Transactions of the British Mycological Society 17: 237-295D. medusaea

Mathias Hass, 07-03-2026 08:48

Re : Is this Diaporthe rudis?

It is for sure a Diaporthe sp. Ellis&Ellis Microfungi on Land Plants has two species on Hedera (so does Wehmeyer), namely D.pulla and D.hederae. Bladmineerder.nl has a D.helicis in addition to the former two. D. rudis is a taxon with a broad host spectrum, but it seems not to be mentioned on Hedera. In many (or most) cases it is not possible to distinguish Diaporthe species on basis of morphology. Based on Ellis&Ellis your find seems to be D.pulla which has more slender spores compared to D. hederae. D.helicis is listed by Wehmeyer under D.eres (s.l.) on Hedera and possibly conspecific with D.pulla. A more recent paper suggests that D.pulla and D.helicis are different (molecular data), although closely related specis: see "Insights into the genus Diaporthe: phylogenetic species delimitation in the D. eres species complex" Udayanga et al. 2014. The same paper mentions that D. hederae may be conspecific with D. rudis (based on an ITS sequence).

The observed conidia are not from Diaporthe/Phomopsis.

cheers Mathias

Mathias Hass, 07-03-2026 21:08

Re : Is this Diaporthe rudis?

Yep, it is a horrible situation :-) ... when some species are mono/oligophagous while other closely related species are polyphagous, but with almost identical morphology...multi-locus sequenceing seems to me the only option. Diaporthe far from the only group. Evolution i progress i guess :-)

cheers Mathias