New locations for embergeria rust on the Chatham Islands

Embergeria or Chatham Islands sow thistle (Sonchus grandifolius) is the largest indigenous representative of the sow thistles in the New Zealand archipelago. The species is endemic to the Chatham Islands, where it is known from all of the larger vegetated islands except the Motchu Har / Forty-fours, Rakitchu / Rangitutahi / Sisters, Motchu Hop’ / Star Keys and Tcharok’ / Tarakokoia / The Pyramid. Embergeria was formally described as Sonchus grandifolius by Wellington-based botanist Thomas Kirk (18 January 1828 – 8 March 1898) using specimens collected by Henry H. Travers (October 1844 – 16 February 1928) from an unspecified location on the Chatham Islands (Kirk 1894). These specimens were lodged in what is now the herbarium of Te Papa Tongarewa Museum of New Zealand by that museum’s resident botanist John Buchanan (13 October 1819 – 18 October 1898), where they were then worked on by Kirk. The genus Sonchus in which embergeria was placed by Kirk is the same genus to which the more familiar, common sow thistles Sonchus asper and S. oleraceus. (often referred to as puha or puwha) also belong. There embergeria remained until 1965 when Egyptian-based botanist Loufty Boulos (14 May 1932 – 27 April 2015) erected the genus Embergeria, in which he placed Sonchus grandifolius and the Australian S. megalocarpus Hook.f. as Embergeria grandifolius and E. megalocarpa respectively (Eichler 1965). The Chatham Islands species was made the type of that genus, and so when E. megalocarpa was placed in its own genus Actites Lander, as A. megalocarpus (Hook.f.) Lander (Lander 1976), the Chatham Islands plant became the sole representative of the genus Embergeria. There it remained until 2014 when it was decided to return it to Sonchus (Garnock-Jones 2014).

Taxonomic changes aside embergeria (the vernacular by which it is now widely known) remains one of the iconic Chatham Islands endemic plants. The species is a feature species of those intact, indigenous dune fields and coastal headlands on the islands. At one time, embergeria was regarded as seriously at risk of extinction but fencing of the coast, replanting of ailing populations and translocation to secure sites have reversed the trend and the species is now listed as ‘At Risk / Recovering’ (de Lange et al. 2018). Whilst this is good news for the species, a rust fungus, Puccinia embergeriae, endemic to it has not fared so well.

Puccinia embergeriae was first recognised in the wild from specimens collected from Kaingaroa Point and nearby Kaingaroa Beach during a November 1992 field trip there by New Zealand-based mycologists Eric McKenzie and Peter Johnston (McKenzie & Johnston 2004). These initial collections were of the rusts uredinial stage during which the rust produces asexual urediniospores (Fig. 4). Later in April 1993, aside from the uredinia, telia (the sexual spores of the species) were found, enabling a complete description of the rust fungus to be made (McKenzie & Johnston 2004). To date Puccinia embergeriae has only been found on embergeria, so in common with many rust species it is very host-specific. Even in places where the other indigenous Sonchus on the islands, S. kirkii Hamlin grows alongside rust-infected embergeria plants the rust holds true to its sole host S. grandifolius. This probably means that Puccinia embergeriae has had a long-standing relationship with its host plant embergeria. Heenan et al. (2010) suggested that embergeria and Kirkianella also now treated as Sonchus (Garnock-Jones 2014) diverged from each other sometime between 1.41 and 12.68 million years ago. This is plenty of time for the host specific relationship of Puccinia embergeriae and embergeria to develop.

Although ‘embergeria rust’ as it has come to be known has been formally recognised for 17 years now, very little is known about the species distribution; until 2004 all known collections of the rust had been made from Kaingaroa Point (the type locality for the species), and nearby Kaingaroa Beach (McKenzie & Johnston 2004). In 2006 when I first saw this rust in the wild at Kaingaroa Point with the late John Sawyer (de Lange 2015), John and I knew of the rust but assumed it would be very hard to find. Amazingly it wasn’t. Embergeria plants infected with Puccinia embergeriae are easily spotted, as the rust forms 5−15 mm diameter, more or less circular lesions on the host plant leaves. On the upper leaf surfaces of embergeria these lesions form the classic ‘traffic light’, bulls-eye pattern seen in many rusts, so called because the outer less infected tissue is pale greenish, progressing toward the centre through more or less concentric zones of infected tissue, of yellow / yellow-green, then orange and sometimes red. On the underside of the infected leaf, where the darker central portion of the lesion is topside, is where you find the rust spores, and in the case of Puccinia embergeriae these are pale yellow-brown in urediniospores and blackish brown in teliospores. So as far as field identification of indigenous ‘New Zealand’ rusts go Puccinia embergeriae has proved easy to spot. However, what was also evident, even in 2006 when the host plant embergeria was very common at Kaingaroa Point, was that the rust was very uncommon. John and I examined many hundreds of plants but only found the rust twice.

The ease of identifying Puccinia embergeriae in the field is a boon for surveys for it. From our field recognition of it in 2006 John and I encouraged Department of Conservation staff to search for the rust during their routine plant surveys and management of embergeria populations. Despite these efforts, only one further population was found by Department of Conservation Staff at Ocean Mail in 2004 (B. Gibb s.n., PDD 1017710), an occurrence on planted embergeria (see below). Otherwise following 2006, field knowledge of embergeria rust remained effectively confined to it’s confirmed and assumed continued presence at Kaingaroa Point.

Then during a July 2014 visit to the islands, I found Puccinia embergeriae growing on planted embergeria in the gardens of the visitor car park, Department of Conservation, Te One (P.J de Lange CH2525, PDD 105386). Discussion with Department staff confirmed that the embergeria plants had been raised from seed collected at Kaingaroa Point. So presumably, that is how the rust got there. Unfortunately, despite the importance of this find, the rust infected plants were accidentally removed. The find did, however, raise the possibility of translocating rust infected plants to new sites – which of course may seem a bit odd to some people. Moving diseased plants to new sites? We need to remember the rust is endemic and its relationship to its host plant probably ‘ancient’ (see above). Admittedly limited observations of rust infected embergeria suggests that infected plants are still capable of flowering and setting viable seed with minimal ‘obvious’ damage to the host plant. Not all rusts are evil.

In this respect the discovery in 2008 of embergeria rust at the former Oratia Native Plant Nursery, Oratia, west Auckland was encouraging. Evidently, the embergeria host plants had also been raised from seed collected from Kaingaroa Point (G. Davidson pers comm. October 2008), and presumably, that seed was admixed with rust spores. Here again, we do not know for certain though as embergeria does not flourish in humid climates like Auckland, the rust infected plants died within weeks of the rust being identified. In this case, this observation is also not supported by voucher material.

I left the Department of Conservation in August 2017. My last visit as a Department of Conservation employee to the Kaingaroa Puccinia embergeria had been during May 2008, at which stage Puccinia embergeria and its host plant were still abundant at Kaingaroa Point. I returned to the islands during January 2018 for a four day visit which allowed for a brief search of Kaingaroa Point, where I was horrified to see one embergeria plant left and no rust at all. The former embergeria colony was now completely covered in marram grass (Ammophila arenaria (L.) Link). So, at the type locality for embergeria rust, there was now a good chance it had gone extinct.

This was confirmed when during a November 2018 visit to Kaingaroa Point, a thorough search for embergeria found that it had indeed been extirpated at that location – no host, no rust. However, further west of the Kaingaroa Point, a large population of embergeria was found, and that supported six plants infected with Puccinia embergeriae. That population was revisited during February 2021 and the same number of rust infected plants were found – no others were seen. Further surveys south and west of there found a large embergeria population but no rust.

During the same field trip, Puccinia embergeriae was also observed within embergeria plantings at Ocean Mail c.10 km west of the newly discovered Kaingaroa population. At this site, it has first been observed there in 2004 by then Department of Conservation Botanist Bridget Gibb (PDD 101710) within a location where embergeria had been planted. Although we cannot be certain, it seems rather likely that the Ocean Mail population is not a natural occurrence as the seed source for the plantings of embergeria at this location was Kaingaroa Point, and hitherto there had been no embergeria in that location. So, it seems likely that Puccinia embergeriae spores somehow hitched a ride in seed collected from Kaingaroa Point. Irrespective, considering we were worried the rust was possibly in terminal decline, the 2018 Ocean Mail rediscovery was good news. Later in January 2020, Puccinia was also rediscovered on the dunes above Kaingaroa Bay, near the rehabilitated rubbish dump. Here it had been found in 1992 by Eric McKenzie and Peter Johnston (PDD 61888), then again in 2006 by the late Ross Beever (R.E. Beever 2670, PDD 94472) though also good news was restricted to recently planted embergeria, also it transpires of Kaingaroa Point provenance.

So, at the onset of 2020, we knew of three extant Puccinia embergeriae populations, one natural, two probably stemming from accidental translocation of infected host plants (c.f., Denchev et al. (2015)). What was peculiar though, was that despite patient searching we still had not found the rust anywhere else on the islands.

On the 23 of December 2020, I was on Rēkohu (Chatham Island) again, and during that visit, I took the opportunity to walk Waitangi West Beach. This large sandy beach is a known strong hold for Atriplex billardierei. However, it also supports populations of other uncommon Chatham Islands plants such as pingao (Ficinia spiralis), kopakopa (Myosotidium hortensia), and embergeria. Toward the southern end of the beach, careful searching of embergeria located a new, presumably natural, population of embergeria rust (P.J. de Lange CH4026, UNITEC 12703 (PDD)) (Fig. 5).

The embergeria rust population at Waitangi West is so far the largest I have seen; most plants within the southern third of the beach are infected with the rust. In common with all embergeria rust infections I have seen, the plants foliage though sporting numerous rust lesions, was heavily flowering and/or setting fruit. Visually at least, the rust still does not seem to seriously damage the host’s ability to reproduce.

Later in February 2021, a coastal Lepidium survey provided the opportunity to check a wide range of embergeria populations for the rust. However, despite diligent searching, no further populations were found in those embergeria populations present along the coastline between Ocean Mail and Wharekauri, and on the coastline of Waitangi West Farm, on Rēkohu (Chatham Island). A brief inspection of embergeria populations at the northern end of Rangihaute (Pitt Island) found no sign, nor did a thorough check of host plants on Wharekaikite (Rabbit Island).

Embergeria rust as an endemic disease will probably always remain a conservation issue that most people will struggle to see worthy of management effort. However, it is now a part of the ecology of Sonchus grandifolius, a rust engaged in a dance with its host that has gone on for millennia. We need to remember that such relationships are an important part of our contribution to global diversity. It is to be hoped that this article will now stimulate further finds of embergeria rust on the Chatham Islands.

Acknowledgements

I would like to thank Erin Patterson, Tom Hitchon (Chatham Islands Department of Conservation), Bridget Gibb (Owenga, Rēkohu (Chatham Island)) and Theo de Lange for their interest in embergeria rust, company in the field, and also for helping find new locations for this rust. I thank Susan Thorpe for providing the imi ta re names for the outer islands of the Chatham Islands group. Thanks also to Luzie Schmid for her considered comments on a draft of this article.

References

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  • Denchev, C.M.; McKenzie, E.H.C.; Denchev, T.T. 2015: Puccinia embergeriae McKenzie & P.R. Johnst. In: The Global Fungal Red List Initiative. http://iucn.ekoo.se/iucn/species_view/370658/. (accessed: 10 May 2021)
  • Eichler, H. 1965: Supplement to J. M. Black’s Flora of South Australia (2nd Ed.). Adelaide
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  • Heenan, P.B.; Mitchell, A.D.; de Lange, P.J.; Keeling, J.; Paterson, A.M. 2010: Late-Cenozoic origin and diversification of Chatham Islands endemic plant species revealed by analyses of DNA sequence data. New Zealand Journal of Botany 48: 83–136
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  • McKenzie, E.H.C.;  Johnston, P.R. 2004: Puccinia embergeriae sp. nov. on Chatham Islands sow thistle (Embergeria grandifolia) and a note on Miyagia pseudosphaeria on sow thistles (Sonchus spp.) in New Zealand, New Zealand Journal of Botany 42: 657–661.

Associate Professor (Botany, Ecology, Plant Conservation, Biosystematics) at Unitec in Auckland and a former Department of Conservation scientist. Peter has been visiting the Chatham Islands since 1996 and is a current member of the Chatham Islands Conservation Board.