Puccinia saccardoi

The fungus is a plant rust. It shows as open pustules on plants in the genera Goodenia, Scaevola and Velleia. The pustules are of two sorts - aecia and telia. An open aecium is filled with bright yellow aeciospores and an open telium is filled with dark brown to blackish teliospores. Aecia and telia appear on both sides of a leaf.

The species was first described in 1889, based on specimens collected in South Australia, and is found in several Australian states.

Look-alikes

Other plant rusts produce similar pustules. However, the combination of the host plants and features noted above should make this species easy to recognize.  

The following paper discusses the rusts on Goodeniaceae:

A. R. McTaggart, A.D. W. Geering & Roger. G. Shivas, 2014, The rusts on Goodeniaceae and Stylidiaceae, Mycological Progress, 13, 1017–1025.

and some of the information given in that paper appears also on this website:

https://collections.daff.qld.gov.au/web/key/rustfungi/Media/Html/index.html