Campbell Island, Mt. Honey, on D. longifolium, March 7, 2000, E.H.C. McKenzie (PDD 87905 – I); fence line from Tucker Cove, on D. longifolium, March 9, 2000, P.R. Johnston (PDD 87907 – I); North West Bay hut, on D. longifolium, March 13, 2000, P.R. Johnston (PDD 87906 – I).

Pycnia not seen. Aecia mainly on abaxial surface, pale, linear, lying between the parallel leaf veins, usually up to 1(–1.5) mm long, ca. 0.25 mm wide, usually only 2–4 per leaf and lying end to end, on brown or reddish leaf discoloration that usually extends through to opposite surface of leaf, long covered by the epidermis which ruptures irregularly often along one edge and end of pustule but rarely becomes detached, spores seen when liberated onto leaf surface. Peridium absent. Aeciospores catenate, no separating cells, 17.5–27(–34) × (13–)15.5–21.5 µm (mean of 75 spores, 22.6 × 18.2 µm), obovoid, ellipsoidal or subglobose, often somewhat angular, contents hyaline, wall ca. 0.5 µm thick, hyaline, verrucose, germ pores not seen.

Pycnia ignota. Aecia plerumque abaxialia, pallida, usque ad 1(–1.5) × ca. 0.25 mm, maculis brunneis vel subrufus insidentibus diu epidermidibus obtectis. Peridia nulla. Aeciosporae catenata, 17.5–27(–34) × (13–)15.5–21.5 µm, obovoideae, ellipsoideae vel subglobosae, saepe angulatae, interne hyalinae, membrana ca. 0.5 µm crassa hyalina verrucosa, poris germinationis ignotis.

Notes: The genus Petersonia was erected by Cummins and Hiratsuka (2003) to accommodate those rusts producing aecia that lack a distinct peridium and have catenate aeciospores without separating cells; this is Caeoma type IV and V of Sato and Sato (1985), and would include the aecial states of Mikronegeria and Blastospora. To date the genus is monotypic with only the original species, P. sanctaecrucis (Espinosa) Cummins & Y. Hirats., the aecial state of Mikronegeria fagi Dietel & Neger, which occurs in the Andes in Chile and Argentina and produces telia on Nothofagus and aecia on Araucaria. Some other species with a similar aecial morphology have been described in the genus Caeoma; these include C. peltatum C.G. Shaw III & C.G. Shaw described from New Zealand on cladodes of Phyllocladus trichomanoides D. Don (Shaw 1976). The aeciospores of C. peltatum are somewhat larger (23.8–46.3 × 17.5–30 µm, mean 32.7 × 25.3 µm) with a thicker wall (1–2.1 µm) than those of Petersonia dracophylli.
The host genus, Dracophyllum (or “grass tree”), is placed within the mainly Southern Hemisphere, predominantly Australian family Epacridaceae. Almost 40 species of Dracophyllum occur in New Zealand with a few species in New Caledonia, and 1 or 2 in Australia. This is the first record of a rust fungus on the genus.

Campbell Island, east of Beeman Hill, on Dracophyllum longifolium (J.R. Forst. & G. Forst.) R. Br. [Epacridaceae], March 6, 2000, P.R. Johnston & E.H.C. McKenzie (PDD 87909 – I – HOLOTYPE)