Ecological communities of Aotearoa / New Zealand species threatened by myrtle rust (Austropuccinia psidii (G. Winter) Beenken): The flora and mycobiota of the endemic genus Lophomyrtus Burret

The invasive rust Austropuccinia psidii, responsible for myrtle rust disease, poses a serious threat to the New Zealand Myrtaceae. Since the 2017 detection of Austropuccinia psidii in Aotearoa / New Zealand, the rust has spread rapidly, resulting in the decline and death of a range of indigenous Myrtaceae, most notably the two species of the endemic genus Lophomyrtus, ramarama (L. bullata) and rōhutu (L. obcordata). While the threat Austropuccinia psidii poses to Lophomyrtus is now widely recognised, the indirect impact the rust has on the associated biota is poorly understood. Very little has been documented about the biota found in association with Lophomyrtus. To rectify this, we undertook a survey of the specimens held in three of the key Aotearoa / New Zealand herbaria that had been collected from Lophomyrtus. This was supplemented by field work in eight sites in western Te Ika a Maui / North Island, and north-western Te Wai Pounamu / South Island of Aotearoa / New Zealand. Although the herbarium searches located few specimens, and field work was limited to a few sample points within the range of Lophomyrtus, we found 221 taxa associated with Lophomyrtus, 176 taxa on ramarama, 81 on rōhutu and one on the naturally occurring hybrid between these two species Lophomyrtus ×ralphii. Of the 176 taxa found on ramarama, 59 are bryophytes (one hornwort, 33 liverworts and 25 mosses), five pteridophytes, 16 spermatophytes and 96 are lichenised mycobiota. Rōhutu supported 81 taxa: comprising one cyanobacterium, one alga, twenty-nine bryophytes (17 liverworts and 12 mosses), four pteridophytes, two spermatophytes and 44 lichenised mycobiota. Wild populations of Lophomyrtus ×ralphii were not investigated, and herbarium searches only disclosed one plant, the mistletoe Korthalsella lindsayi, associated with it. Several lichens and liverworts collected from Lophomyrtus represent potentially new species, and Lepra erythrella is a new addition to the lichenised mycobiota of Aotearoa / New Zealand. None of the putative new species are endemic to Lophomyrtus.