This is a plant parasite that produces bright or dark spore-holding pustules on the stems and leaves of species of Linum. Bright yellow asexual spores and black sexual spores are produced at at different stages of this rust's life cycle and the pustules rupture to release the spores. The authors of the paper listed below illustrate and explain the life cycle on pages 350-352.
This is an introduced species and by 1906 (see the McAlpine reference) had been reported from NSW, SA, Tasmania and Victoria.
This rust is distinctive as long as you know that the host is a species of Linum. Different rusts produce similarly coloured spores on other plant genera.
G. J. Lawrence, P. N. Dodds & J. G. Ellis, 2007, Rust of flax and linseed caused by
Melampsora lini, Molecular Plant Pathology, 8, 349–364.
D. McAlpine, 1906, The rusts of Australia, Government Printer, Melbourne.
Melampsora lini is listed in the following regions: