For a description of the damage caused to the plant, see Elm Leaf Deformation .
The mycelium is annual, develops under the cuticle of the plant.
The marsupial layer (“ hymenia ”) has the appearance of a waxy powdery coating on the lower surface of deformed leaves, less often on the upper surface, grayish or brown in color [1] . Asuka in “hymenia” do not form a continuous layer [2] .
Ascores are eight-spore, less often four-spore, 10–29 × 7-15 [2] microns in size, according to other sources 12–80 × 8-10 [1] microns, cylindrical or ellipsoidal with rounded apices. The basal cells ( see Tafrin's article ) are wide, measuring 15–20 × 8–11 μm [2] .
Ascospores are rounded, 3-5-5 microns in size, begin to bud after exiting the ascus (yeast cells with a diameter of 3-8 microns are often found on the surface of affected leaves). Taphrina ulmi also observed a characteristic method of budding of spores in the asks, in which perforation of the membranes occurs and daughter blastospores appear on the surface of the asks [2] .
Taphrina ulmi is distributed over a large territory of Europe and North America , is also known in the Caucasus , Central Asia and Kazakhstan .
It affects various types of elm ( Ulmus ), the typical host is Elm ( Ulmus minor ). It is also found in Europe on elm ( Ulmus glabra ) elm, smooth elm ( Ulmus laevis ), in America - on American elm ( Ulmus americana ), Ulmus alata , Ulmus rubra [2] .
Rounded or irregular, angularly shaped spots of 0.5–2 cm in size appear on the leaves, the affected part of the leaf blade is slightly swollen (convex-concave). Spots can merge and cover a significant part of the leaf. The color of the spots is yellowish, grayish or brown, subsequently the spots turn black, the affected part of the leaf dies and falls out. Although severe leaf damage can occur in some years, the disease is usually not considered harmful. Tangible damage from deformation of elm leaves was recorded only in the Crimea , where the disease is accompanied by deformation of shoots and causes damage to young plantations [2] [1] [3] .