cfia-acia's Identifications

Possibly. Need second observation on oats, wheat, barley or even orchardgrass (?) - see https://apsjournals.apsnet.org/doi/10.1094/PDIS-05-19-1089-PDN (primary host) - Berberis is secondary host - see related observations
http://www.inaturalist.org/observations/75508521
https://www.inaturalist.org/observations/165625021

Separate fungal observation on fescue
http://www.inaturalist.org/observations/121046934

Cumminsiella mirabilissima Puccinia striiformis also to consider.
Photo 1: Underside of Berberis leaf - Orange aecia puffing out and distorting leaf shape
Photo 2: Side view top of darkened spermagonium - greyish white receptive hyphae tufting out
Photo 3-4: Hyphae showing branching sections, with some small spermatia. Hyphae approx 60um long, 2-3 um wide
Photo 5-6 Aeciospores n=8 (20-35)x(15-25) um - see two aeciospores top right - ?'Equatorial germ pore'?
Photo 7 - Sticky exudate from top of black spermatogonium
Will need to return in autumn to see if grasses show Teliospores. Will attach images if found.
On review of photo 7 - note small papilla and extended pedicel in some instances of the urediniospores - see desc http://www.zor.zut.edu.pl/Mycota/Cumminsiella%20mirabilissima.html

Extension of host range from Mahonia to Berberis
http://www.inaturalist.org/observations/165625021? - This is supposedly the 'native plant' section of the garden.

10/15/2023: Did a cursory check of the grasses nearby (curious to know if Cumminsiella using one as alternate host) - didn't see any obviously blackened grass heads. Teliospores are being parasitized by something like Alternaria : see http://www.inaturalist.org/observations/187985101
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