Taphrina ulmi - Ulmus minor

27 Apr, 2026

Infection in situ on host plant

🌿 Observation

Main diagnostic view of the leaf deformation

While examining elm leaves along the roadside, I noticed irregular reddish patches developing along the veins.

These were not distinct galls, but rather diffuse deformations of the leaf surface. The affected areas appeared slightly blistered and uneven, with a somewhat glossy, swollen look.

Some patches remained isolated, while others had begun to merge into larger, irregularly shaped areas.

🔬 Notes / Identification

Blistered and discoloured leaf tissue visible on both sides

Identification process

I worked through a dichotomous key for galls associated with Ulmus.

The leaf shows irregular, blister-like patches, slightly raised and strongly discoloured. These are not enclosed structures, but diffuse malformations of the leaf tissue.

This rules out:

• aphid galls, which form distinct, closed chambers
• mite erinea, which produce dense, felt-like hair structures

Following the key leads to:

• flat to slightly raised malformations
• without abnormal pubescence
• blister- or patch-like structures, spread across the leaf

This combination points to a fungal cause rather than an insect gall.

What remains is:

→ Taphrina ulmi

(Identification based on a dichotomous key for elm gallers — see Bladmineerders))

🌱 Context / Ecology

Taphrina ulmi is a fungus that causes leaf distortions on elm species.

• Infection: Occurs on developing leaves in spring
• Effect: Induces abnormal growth, resulting in blistered, discoloured patches
• Structure: No enclosed gall; the fungus lives within the leaf tissue
• Appearance: Reddish to brownish patches, often following veins

Although often grouped with galls, this is not a true gall but a fungal deformation of plant tissue.

These infections can become more extensive over time, with patches merging and covering larger portions of the leaf.

📎 Related

• Tetraneura caerulescens – Ulmus minor
• Tetraneura nigriabdominalis – Ulmus minor

#Gall