#rust fungus

11/16/2025, Southeast Virginia

Nældegalle-Tvecellerust (Puccinia urticata)

På stor nælde (Urtica dioica).

Nettle Clustercup Rust Fungus (Puccinia urticata)

Rust fungus (Puccinia sp.) growing on biscuitroot (Lomatium dissectum)

Puccinia urticata on Urtica dioica

It’s hard to walk by banks covered in common nettle without noticing this fiery and gruesome rust fungus taking hold of and deforming the plant’s limbs. 

It’s best described as a species complex with a life cycle which might alternate between two hosts- in the British Isles often a nettle (U. dioica or U. urens) and a sedge (mostly Carex sp.), but its ‘sub-species’ can also be found on Aster and Ribes.      

And then, tonight, as I was getting these photos together to post on my blog, I noticed that many of the Sowthistle leaves had little yellow pimples on them, surrounded by dark pinkish rings - it soon figured out that it’s a another specialist, the Sonchus Rust Fungus (Miyagia pseudosphaeria).

Rust fungi can be terrible agriculturally but are fascinating nonetheless. This is Gymnosporangium sp. growing on juneberry fruits. All species of Gymnosporangium have two hosts where their life cycles are divided. The primary host is the juniper tree, where it fruits and produces spores to infect the secondary host - in this case, a juneberry tree. The white parts are spore tubes, and the orange dust is the spores.