Syzygium maire is a tree endemic to Aotearoa / New Zealand where it occurs on Te Ika a Maui / North Island and Te Wai Pounamu / South Island. A few trees are also recorded on offshore Islands off of North Island, including on Aotea / Great Barrier Island, Hauturu-o-Toi, Little Barrier Island and Kapiti Island. The species is considered widespread in parts of its range, and as scarce in other parts. A population of ≥100,000 mature trees is still likely. This species is one of the indigenous myrtles most vulnerable to the myrtle rust disease (Austropuccinia psidii), and this is now the main threat to the S. maire. It is suspected that over the next generation (100 years) Austropuccinia could rapidly reduce the population of S. maire and cause a decline of over 80%. It is assessed as Critically Endangered.

This species is endemic to Aotearoa / New Zealand where it occurs on Te Ika a Maui / North Island and Te Wai Pounamu / South Island (Golden Bay, Nelson, Marlborough Sounds and Rarangi). A few trees are also recorded on offshore Islands of North Island, including on Aotea / Great Barrier Island, Hauturu-o-Toi, Little Barrier Island and Kapiti Island.

There has been no nationwide population estimate. However, the species is widespread in lowland parts of Te Ika a Maui / North Island, with a mostly westerly distribution and scarce in Te Wai Pounamu / South Island. Former strongholds included Tutamoe, Tangihua, northern King Country (Waitomo, Te Kuiti) and the Taranaki. A national population of ≥100,000 mature trees is still likely.

Initially threatened by forest clearance and wetland drainage. Prior to the May 2017 detection of the exotic rust Austropuccinia psidii which causes myrtle rust disease, this species was considered secure at a national level, though scarce over some parts of its range. The main threats remained wetland drainage and animal browsing, especially from possum (Trichosurus vulpecula). At the time of this assessment (2023) Austropuccinia has now increased its range across Aotearoa / New Zealand, and one of the most vulnerable indigenous myrtles has proved to be Syzygium maire. Austropuccinia infections were first detected on this species in April 2018 and by 2022 tree deaths from this rust were being reported from throughout Northland, Auckland, Waikato, and Taranaki. While the rust is now the key threat to this species, animal browsing and wetland drainage remain ongoing issues.

Over the next 100 years Austropuccinia could rapidly reduce the global population of S. maire and cause a population decline of over 80%. The species is long-lived (over 300 years) and following IUCN Guidelines future decline should not be calculated for more than 100 years. A generation length of 100 years is used and the 80% population decline is likely to occur in one generation of the species.

Syzygium maire is a tree reaching up to 16 m tall, the trunk base often develops knees and where the root plate is exposed usually bears pneumatophores (sometimes also produced on the lower trunk). Between November and July this species may flower, though flowering usually peaks during summer. The red-fleshed fruits are bird dispersed, with the seeds usually germinating in pools of water or mud puddles. Syzygium is a species of coastal and lowland riparian forest and coastal wetlands growing in waterlogged ground, on the margins of swamps, lakes and stream and river sides (de Lange 2023). It is also found in montane and cloud forest associations of Northland, the western Waikato, and the lower margins of Egmont National Park where high rainfall and poor drainage provide ideal conditions for this tree to establish on hill slopes, tablelands and within karst landscapes. In good conditions Syzygium may form the canopy along the margins of forested water ways, gulley bottoms on poorly draining soil, or on the margins of fertile freshwater wetlands. Common co-associates include Dacrycarpus dacrydioides, Laurelia novae-zelandiae, Elaeocarpus hookerianus, Cordyline australis, and Hedycarya arborea. 

It was initially threatened by forest clearance and wetland drainage. Prior to the May 2017 detection of the exotic rust Austropuccinia psidii which causes myrtle rust disease, this species was considered secure at a national level, though scarce over some parts of its range. The main threats remained wetland drainage and animal browsing, especially from possum (Trichosurus vulpecula). At the time of writing (2023) Austropuccinia has now increased its range across Aotearoa / New Zealand, and one of the most vulnerable indigenous myrtles has proved to be Syzygium maire. Austropuccinia infections were first detected on this species in April 2018 and by 2022 tree deaths from this rust were being reported from throughout Northland, Auckland, Waikato, and Taranaki. While the rust is now the key threat to this species, animal browsing and wetland drainage remain ongoing issues.

As this species is difficult to maintain in cultivation it is not known to be commercially available (de Lange 2023). Syzygium maire is not often cultivated, though it is an attractive tree. The seed is difficult to store, and cannot be allowed to dry out, with only short-term viability (a matter of weeks or months) (van der Walt et al. 2021) the species is not well served by seed-banking. Many cultivated trees in the Auckland Region have died from Austropuccinia infections.

The key threat to Syzygium maire is Austropuccinia psidii. All other known threats can be effectively managed but the rust, so far, has not been. The impact on Syzygium maire is considered severe, infections resulting in the death of seedlings, saplings, and mature adults (these within as little as two years). As the rust continues to spread, and infections increase, there will be more spores spread, so the severity in infections of host plants is anticipated to increase. Currently there is no known cure for Austropuccinia, all that can be hoped for is that some lineages of host plants have or develop resistance. 

As the rust is wind dispersed quarantine measures are also ineffective. The seed of Syzygium has short-term viability so seed storage is of limited value. Current measures to secure the species should consider holding tissue-cultures. Consideration should be given to cultivating the species outside the global distribution of Austropuccinia, to see if at those sites the species can be secured in Botanic Gardens and other threatened plant collections.

Research into finding a cure for Austropuccinia is a global issue and many organisations are working in this area. Like all research however, those investigations are subject to funding issues and political whim. Austropuccinia is a global problem, a global response is needed – only time will tell if humanity understands the consequences of the loss of the Myrtaceae on world ecosystems and takes the right steps to find solutions to help manage this rust.

New Zealand Threat Classification System assessed this species as ‘Threatened / Nationally Critical’ Qualified ‘DP’ [Data Poor] (de Lange et al. 2018) citing criterion ‘C’ viz., ‘population (irrespective of size or number of subpopulations) with a very high ongoing or predicted decline of >70%’ – at the time that assessment was done (May 2017) it was precautionary, events have transpired to show it was, unfortunately correct.