Puccinia hieracii

Probably a species complex, best treated in a broad sense as 'sensu lato'.  Galls on the above hosts are treated as this in Redfern & Shirley (2023).  The complex includes the following named species that may be identical with or varieties of P. hieracii; see 'Plant Parasites of Europe' website for more details: 

Knapweeds (Centaurea), Puccinia jaceae
Cat's-ear (Hypochaeris), Puccinia hypochaeridis
Mouse-ear Hawkweed (Pilosella), Puccinia piloselloidearum
Chicory (Cichorium intybus), Puccinia cichorii
Dandelions (Taraxacum), Puccinia taraxaci 
Hawkweeds (Hieracium), Puccinia hieracii
Hawkbits (Leontodon and Scorzoneroides), Puccinia leontodontis
Ox-tongues (Picris and Helminthotheca), Puccinia picridis
Saw-wort (Serratula tinctoria), Puccinia tinctoriicola

The rust fungus Puccinia hieracii causes galls in several Asteraceae genus - e.g. Knapweeds (Centaurea),  Hawkweeds (Hieracium), Hawkbits (Leontodon/Scorzoneroides), Ox-tongues (Helminthotheca/Picris), Mouse-ear Hawkweed (Pilosella), Saw-wort (Serratula) and Dandelion (Taraxacum).     

Typically, the gall is a thickened deformed leaf with reddish-yellow spots bearing spermogonia, followed by uredinia and telia.  [N.B.: it is not clear if aecia are produced; in Redfern and Shirley (2023) this stage in mentioned; 'Plant Parasites of Europe' states that aecia are missing.]

Similar species of rust, some gall-causing, can occur on these species - e.g. Puccinia calcitrapae on Knapweed.  Puccinia variabilis on Dandelions has small orange aecia but is not thought to be a gall-causer. 

host/microscopy

Photograph the rust on the host.  Ensure you have noted the host-plant species in your comments.  On some hosts, microscopic examination may be needed.

on various grassland or waste-ground species in the Asteraceae