A new Chatham Island lichen – Zwackhia viridis

The lichenized mycobiota of the Chatham Islands is still poorly known. Since 2008 there has been a major effort to collect lichens from the islands. From those collections, lichenologists working in the UNITEC herbarium, Unitec New Zealand Institute of Technology campus in Auckland, are beginning to make a number of interesting discoveries. Here we report the discovery of Zwackhia viridis a crustose graphid lichen that represents a new genus and species for the Chatham Islands, and for that matter New Zealand.

Our knowledge of the Chatham Islands lichenized mycobiota is steadily growing from the 48 species recognized from the islands by the late David Galloway (Galloway 2007). Since 2008 during visits to the islands there has been a concerted effort to collect lichens resulting in a current, as yet unpublished listing for c.352 lichen taxa (de Lange unpubl. data). Along the way a new, seemingly endemic lichen, Lecanora kohu, has been described from the Chathams (Printzen et al. 2017), a fitting replacement for the previous assumed endemic Caloplaca maculata (Galloway 2004) which has since been found on the coastline south of Dunedin, New Zealand.

As with other lichen listings the most under-represented groups are those with a crustose growth habit, yet ‘lichen crusts’ are the most species rich of the over 2300 lichen taxa currently recognized from the New Zealand archipelago (Marshall et al. 2019). Their under-representation in Chatham Islands lichen collections is in part because they can be hard to collect (especially off rocks) and also because they much harder to identify than many of the larger ‘leafy’ (foliose) lichens. Identification often requires a myriad of chemical spot tests not only of the lichen thallus, but the fruiting bodies internal structure, spore bearing asci and the spores (ascospores) themselves. Noting the colour reactions (or lack thereof) using potassium hydoxide (KOH) – the ‘K’ test, iodine – the ‘I’ test, and para-phenylenediamine – the ‘Pd’ test are critical; as also is whether the various lichen structures fluoresce under an ultra-violet light. Even with those tests, and careful measurement of ascus and ascospores, further testing using thin-layer chromatography and DNA sequencing may still be necessary.

When working with lichens one soon accepts that collecting them is easy but identifying them takes way longer.

Accepting then that Chatham Island lichen crusts are still poorly collected, since 2018 there has been renewed effort to sample crustose lichens. Lichen crusts are more varied than people would think, they come in all different shapes and sizes, and many are stunningly beautiful, others, well, they truly fit the adage ‘beauty is in the eye of the beholder’.

At Auckland’s Unitec Institute of Technology (now included in a larger New Zealand Institute of Technology) staff have started to work over more carefully the crustose lichens of the northern North Island, and, as specimens are received, those from the Chatham Islands. Last year the call was made to sample better the Chatham Island lichens of the genus Pyrenula. Pyrenula are a great example of ‘beauty is in the eye of beholder’, most specimens resemble a splotch of greenish or whitish-coloured dried varnish covered in black spots (Fig. 1.). Identification requires digging out the black spots (the spore bearing perithecia) and extracting the spores – usually a fiddle and all too often one finds mites have beaten you to it and eaten all of the spores.

Pyrenula nitidula Nikau Bush — Fig. 1. *Pyrenula nitidula* as seen growing on the trunk of nikau (*Rhopalostylis sapida*), Nikau Bush Conservation Area, Rekohu / Wharekauri / Chatham Island (image: P.J. de Lange).

Fig. 1. *Pyrenula nitidula* as seen growing on the trunk of nikau (*Rhopalostylis sapida*), Nikau Bush Conservation Area, Rekohu / Wharekauri / Chatham Island (image: P.J. de Lange).

Despite this all too common annoyance, last year during visits to Rekohu / Wharekauri / Chatham Island a range of Pyrenula lichens were collected. Lichen crust collections are rarely ‘pure’ samples of one species, they often comprise admixtures of several lichens growing interdigitated. One such Pyrenula sample came from nikau (Rhopalostylis sapida) (Fig. 2) at Nikau Bush Conservation Area. That sample contained a dominance of Pyrenula nitidula (Fig. 1), and Megalaria maculosa (Fig. 3), there was also another white crustose lichen – a kind of graphid or scribble lichen (Fig. 4).

Fig. 3. *Megalaria maculosa* as seen on the trunk of nikau (*Rhopalostylis sapida*), Nikau Bush Conservation Area, Rekohu / Wharekauri / Chatham Island (image: P.J. de Lange).

Zwackhia viridis thallus Nikau Bush — Fig. 3. *Megalaria maculosa* as seen on the trunk of nikau (*Rhopalostylis sapida*), Nikau Bush Conservation Area, Rekohu / Wharekauri / Chatham Island (image: P.J. de Lange).

Graphid lichens are the common name given to a grouping of lichens whose fruiting bodies (lirellae) often look like black scribbles or lines (Fig. 5). Whilst many of the various genera of graphids were once all placed in the same family – the Graphidaceae; following patient study and interpretation of DNA data has shown that the “Graphidiaceae” and the graphid habitat contain a large a range of families that are not necessarily that closely related to each other. It would seem that the ‘graphid lichen’ morphology has arisen several times, and that even some lichen genera that lack lirellae are in the same family as those that do.

Arthonia atra Kaingaroa — Fig. 5. *Arthonia atra* showing the classic ‘scribbly’ fruiting bodies (lirellae) that give the common name ‘graphid’ to these sorts of lichens. This specimen was noted on the trunk of Chatham Island ngaio (*Myoporum semotum*), Kaingaroa Rekohu / Wharekauri / Chatham Island (image: P.J. de Lange).

Fig. 5. *Arthonia atra* showing the classic ‘scribbly’ fruiting bodies (lirellae) that give the common name ‘graphid’ to these sorts of lichens. This specimen was noted on the trunk of Chatham Island ngaio (*Myoporum semotum*), Kaingaroa Rekohu / Wharekauri / Chatham Island (image: P.J. de Lange).

The one found on the nikau bark sample however, was a clear cut graphid, though in this case the black lirellae were rather unprepossessing (Fig. 4)

Preliminary examination suggested that the graphid ‘by catch’ in the nikau sample might be a species of Opegrapha. However, the Chathams specimen has very long (42.5 × 6-8 μm), fusiform ascospores (Fig. 6), each bearing up to 18 tabular locules (compartments). Unable to resolve the probable species, images were taken and sent to Dr Robert Lücking in the Botanischer Garten und Botanisches Museum, Berlin. Robert suggested that the specimen might be a species in the genus Zwackhia, and as we lacked the critical literature, he kindly sent an electronic copy of Ertz (2008).

Leucopogon parviflorus Kaingaroa — Fig. 8. *Leucopogon parviflorus* a species of ‘mingimingi’ abundant on Rekohu / Wharekauri / Chatham Island which is otherwise only known from eastern Australia. It has never been found in the main islands of New Zealand (image: P.J. de Lange).

Ertz (2008) did a major revision of the bark-inhabiting (corticolous) Opegrapha (some of the species he treated then as that Opegrapha are now placed in Zwackhia). To work the key to the “Opegrapha” in Ertz (2008) also required another range of extremely fiddly dissections of the lirellae, including cutting cross-sections and then staining those with a sequence of iodine and potassium hydroxide to check for colour reactions (Fig. 7). Though a protracted process the result was a definitive identification of the Nikau Bush specimen as an example of Opegrapha viridis – now treated as Zwackhia viridis.

Zwackhia viridis has hitherto not been recorded from the New Zealand archipelago (de Lange et al. 2018), it is an eastern Australian species (Ertz 2008 – as Opegrapha viridis). With a distribution such as this, its presence on the Chatham Islands probably means it has been overlooked in New Zealand, or more likely, it has already been collected and lodged within our nations herbaria but such specimens have as yet not been recognised as that species. While it is unlikely that Zwackhia viridis has somehow bypassed the larger islands of New Zealand to make landfall on the Chatham Islands this biogeographic anomaly is still possible. After all, Leucopogon parviflorus (Fig. 8), a locally common Chatham Islands shrub which is most seen in the sand country on Rekohu / Wharekauri / Chatham Island is also native to and abundant along the coastline of eastern Australia and Tasmania. This species does however bypass the North, South and Stewart Islands of New Zealand, its only known occurrence outside Australia is the Chatham Islands.

If Zwackhia viridis also does this, only dedicated collecting throughout New Zealand and patient hours spent behind a microscope will truly tell. For now, all we can say is that we are still adding to our knowledge of the lichen mycobiota of the Chatham Islands, and for New Zealand as a whole we have added another species, and in this case a genus to the national tally of lichens.

Acknowledgements

Thanks to Dr Robert Lücking for his help guiding us to the identity of Zwackhia viridis.

References

de Lange, P.J.; Blanchon, D.J.; Knight, A.; Elix, J.; Lücking, R.; Frogley, K.M.; Harris, A.; Cooper, J.A.; Rolfe, J.R. 2018: Conservation status of New Zealand lichens and lichenicolous fungi, 2018. New Zealand Threat Classification Series 27: 1–64.
Ertz, D. 2008: Revision of the corticolous Opegrapha species from the Palaeotropics. Bibliotheca Lichenologica 102. 176p.
Galloway, D.J. 2004: New lichen taxa and names in the New Zealand mycobiota. New Zealand Journal of Botany 42: 105–120
Galloway, D. J. 2007a: Flora of New Zealand – Lichens (revised second edition). Manaaki Whenua Press, Lincoln, New Zealand.
Marshall, A.J.; Blanchon, D.J.; Aptroot, A.; de Lange, P.J. 2020: Five new records of Pyrenula (Pyrenulaceae) for New Zealand. New Zealand Journal of Botany 58: 48–61
Printzen, C.; Blanchon, D.J.; Fryday, A.M.; de Lange, P.J.; Houston, D.M.; Rolfe, J.R. 2017: Lecanora kohu, a new species of Lecanora (lichenised Ascomycota: Lecanoraceae) from the Chatham Islands, New Zealand. New Zealand Journal of Botany 55: 439–451

Andrew Marshall

Andrew Marshall is a graduate from the School of Environmental & Animal Sciences, Unitec New Zealand Institute of Technology. Since his graduation Andrew started and now runs a successful environmental consultancy undertaking biodiversity assessment and monitoring throughout the Auckland Region. Andrew is a also a lichenologist who specialises in the identification of crusts, he has amongst other new lichen discoveries for New Zealand, described in 2019 the new lichen species Ocellularia jacinda-arderniae.

Peter J. de Lange

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.