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Diplocarpon mespili also called Entomosporium m. because the conidium resembles an insect. Conidia are made of cells arranged symmetrically. Conidia consist of a larger basal cell, an upper cell, and 2 or more smaller, lateral, hyaline cells that form a cross pattern. The apical cell is globose with an obtuse apex; the basal cell is short cylindrical with a truncate base; and the lateral cells are globose. Apical and lateral cells each have a single, cellular, unbranched, flexuous appendage. On Cydonia oblonga (quince). Backyard.

A small, almost invisible organism.
An obligate parasite of Spergularia (Sea Spurrey), causing ‘white rust’ or ‘white blister’.
Sporangiophores appear on the host's stem, causing it to swell and burst. The white powdery spores are then dispersed by wind and rain.

Not very common, not often noticed rust-type (fungal) infection of Dandelion (Taraxacum) leaves. Distorts and discolours the leaf.
Small pustules (sori) occur as the fungus matures
Long lasting through the season and rain.

See https://bladmineerders.nl/parasites/fungi/chytridiomycota/chytridiales/synchytrium/synchytrium-taraxaci/
and
https://www.fungi.org.uk/viewtopic.php?t=177