The plant family Myrtaceae in the Australasian region shows a marked lack of associated indigenous rust fungi (order Pucciniales) as compared to the other main centre of myrtaceous diversity, the neotropics (Walker 1983; Shivas and Walker 1994).

In Australia, only two native rusts are known from myrtaceous hosts: Physopella xanthostemonis (J. Walker) J.A. Simpson, K. Thomas & C.A. Grgurinovic, recorded only twice from the Northern Territory on two species of Xanthostemon, and Puccinia cygnorum R.G. Shivas & J. Walker, in Australia recorded only twice on Kunzea hosts in the Perth region of Western Australia (WA). Black and white photos of the teliosori and teliospores of P. cygnorum are presented in Shivas and Walker (1994); a colour image of the teliosori is presented on the website of the Office of the Chief Plant Protection Officer (2010) (p. 35, Fig. 2.42).

In the course of revision by one of us (ROM) of educational material (Makinson 2012) for a series of Western Australian training workshops on recognition of Myrtle Rust (Puccinia psidii), a need became evident for re-examination of the host species of P. cygnorum in the light of revisionary work on Kunzea by Toelken (1996).

Puccinia cygnorum first came to attention as an unknown fungus on cut foliage imported to New Zealand, where it was intercepted by the quarantine service. It was traced back to a source population in Spearwood, a suburb of Perth, WA, and a voucher collection of rust and host was made (V. Taylor s.n., 13 October 1991). This collection was used as the basis for a teleomorphic species description of P. cygnorum by Shivas and Walker (1994), with holotype at the Western Australian Herbarium (PERTH 1359517) and isotype at the New South Wales Plant Pathology Herbarium (DAR 65768). The host species was recorded and published as Kunzea ericifolia (Sm.) Rchb. ex Heynh.

Subsequently, H.R. Toelken of the State Herbarium of South Australia published a partial taxonomic revision of Kunzea in Western Australia (Toelken 1996). In it, K. ericifolia was re-circumscribed as a species of the far south-west and south coast of WA, well south of Perth. All known populations of K. ericifolia, as now defined, are south of about latitude 33° S (Western Australian Herbarium 1998–), at least 120 km south of the known occurrences of P. cygnorum. A new species, K. glabrescens Toelken was erected by Toelken; this taxon includes the yellow-flowered Kunzea populations in the Perth area formerly regarded as K. ericifolia.

A second collection of P. cygnorum (PERTH 07650205) was made by I.C. Tommerup on 26 November 2002, about 14 km south-east of the type locality, in Jandakot Regional Park adjacent to the suburb of Wandi. The host species was recorded as ‘Kunzea vestita (formerly ericifolia)’. K. vestita Schauer (type: near King George Sound) is now regarded as a synonym of K. ericifolia subsp. ericifolia (following Toelken 1996: 46). The name K. vestita has been misapplied in some influential plant identification literature in the past (e.g. Blackall and Grieve 1980), including to the Perth-area populations now regarded as K. glabrescens.

Langrell et al. (2008: 690) utilised two accessions of P. cygnorum in a molecular study. One is sourced to the type collection. The other sample, coded as ‘E7401’, is not sourced to a voucher, but the associated details—collection date 2002, host ‘Kunzea ericifolia’—make it likely that it was sourced from the Tommerup collection noted above (PERTH 07650205). S.R.H. Langrell (pers. comm. 19 June 2013) confirms this as probable.

The host material included in the two known Australian voucher collections of P. cygnorum is in both cases adequate for confident identification—it includes foliage, inflorescences and infructescences. On current understanding of the taxonomy and distribution of south-west Australian Kunzea, the two P. cygnorum host specimens examined are clearly assignable to K. glabrescens.

In assessing the identity of the two P. cygnorum host specimens at the Western Australian Herbarium (PERTH) it was observed that the young stems (and leaves) were covered in long, straight, widely ascending to spreading hairs. This indumentum is discrepant with the description of K. glabrescens (Toelken 1996: 41) but consistent with the accompanying illustration and caption (loc. cit. p. 42), as well as with the spreading hairs shown on the host in the only semi-published colour photo of P. cygnorum (Office of the Chief Plant Protection Officer 2010), for which no voucher specimen is cited. Stem indumentum was found to be highly variable among the specimens assigned to K. glabrescens at herbaria PERTH and NSW, with the P. cygnorum host plants falling well within the range of variation. On other features the two host specimens conform well to both text and illustrations in the K. glabrescens protologue.

There appear to be few other published references to P. cygnorum and its hosts. Simpson et al. (2006), apparently working from the type specimen only, state that P. cygnorum “is only known from Kunzea ericifolia (Smith) Rchb. ex Heynk. growing in a coastal heathland site near Perth … The host is native to Victoria (Hnatiuk 1990). This suggests the native host of the fungus is another Western Australian species of Leptospermeae or that it was introduced from Victoria.” This statement appears to be based solely on confusion in Hnatiuk’s Census between K. ericifolia (Sm.) Rchb. ex Heynh. of Western Australia, and K. ericifolia F. Muell., a later homonym for which K. muelleri Benth. is now the correct name. K. muelleri occurs in south-eastern Australia (New South Wales and Victoria) and has no connection with the Western Australian rust. There are no indications that either collection of P. cygnorum was made from plants not locally indigenous (e.g. introduced in bush regeneration programs), and the collector’s notes on I.C. Tommerup s.n., 26/11/2002, strongly suggest a natural population (she records that 500 plants were examined in a bushland reserve).

Dick and Inglis (2011) report a 2006 occurrence of P. cygnorum on nursery-sourced cultivated plants of the south-west Australian shrub species Astartea fascicularis (Labill.) DC. in the Napier Botanic Gardens, on the North Island of New Zealand. Eradication actions followed, and subsequent searches on Myrtaceae species in the area have not detected any further occurrence; P. cygnorum was declared eradicated from New Zealand in December 2010. We are unaware of any records of P. cygnorum on A. fascicularis in Australia, although the native distribution of the latter species overlaps strongly with that of Kunzea glabrescens and targeted searches would now be desirable. The fact that both the initial observation of P. cygnorum and this second host-species record were made in New Zealand speaks well for the biosecurity arrangements in that country.

In the light of a fairly high rate of taxonomic revision and nomenclatural change in many plant groups, the case of Puccinia cygnorum indicates a need for periodic review of host vouchers for plant pathogen collections. Databases of both botanical and mycological institutions are possibly now complete and compatible enough for routine searches, informed by recent botanical revisions, to be used to identify potential cases for investigation.