Authors have previously treated plants described by de Lange (2014) as Kunzea tenuicaulis by the name K. ericoides var. microflora based on Leptospermum ericoides var. microflora. However, that variety was described from a garden plant of uncertain origin (confused labelling and protologue), and the lectotype is in sufficiently poor condition as to render its association with plants assumed to that variety impossible (de Lange 2014). Therefore, de Lange (2014) described a new species to encompass those plants confined to geothermally active sites within the Taupo Volcanic Zone of Te Ika a Maui / North Island,. Aotearoa / New Zealand.

Heenan et al. (2024) on the basis of molecular data, used in isolation of other lines of evidence elected to treat all Aotearoa / New Zealand Kunzea as one species K. ericoides. Their work did not consider the morphological and cytological disparity, and other lines of evidence used by de Lange (2014), and the analyses used to derive their conclusions have been disputed by others. The species is accepted by the New Zealand Plant Conservation Network (www.nzpcn.org.nz) and New Zealand Indigenous Vascular Plant Threat Listing Panel.

Kunzea tenuicaulis is a small tree endemic to endemic to Aotearoa / New Zealand, where it is known only from active geothermal ground within the Taupo Volcanic Zone on Te Ika a Maui / North Island. The known area of occupancy is believed to be less than 10 km² but half of the ten known key subpopulations are in protected areas and the other subpopulations are in intact areas, due to them being under private ownership but managed for tourism or near a power station. It was assessed in a precautionary way, ‘Threatened – Nationally Vulnerable’ in 2017 (de Lange et al. 2018), using the New Zealand Threat Classification System, due to arrival of Austropuccinia psidii – which causes myrtle rust disease, which was then believed to be a serious threat to all indigenous Myrtaceae. Since 2023 it is listed as 'At Risk / Naturally Uncommon’ by the New Zealand Threat Classification System (de Lange et al. 2024). The species does remain common on geothermally heat ground where it is usually the dominant woody plant, and is not currently threatened, but it depends on the risk of the the invasive rust Austropuccinia psidii, which can be a long term threat. This species is currently assessed as Least Concern.

This species is endemic to Te Ika a Maui / North Island, Aotearoa / New Zealand, where it is known only from active geothermal ground within the Taupo Volcanic Zone. Distribution map is generalised.

No accurate counts of individuals have been made. However, the species is found only within active geothermal fields covering an area estimated to be <1,000 ha. Within this area there are <20,000 mature individuals spread over 10 main geothermal fields. In these sites it is often the dominant woody plant but it also co-associates with Kunzea robusta and K. serotina with which it sometimes forms complicated introgressive hybrid swarms.

Common on geothermally heat ground where it is usually the dominant woody plant. Near open vents Kunzea tenuicaulis is often decumbent / prostrate, becoming taller away from the more active vents. Some of the decumbent plants retain this attribute in cultivation whereas others assume an arborescent growth habit up to 8 m tall. Irrespective of the growth habit in the wild characteristic of this species is its numerous fine branchlets and pendulous slender branches borne on slender usually multi-trunked base. Within its geothermal habitat other associated plants may include the woody trees and shrubs Kunzea robusta and K. serotina, Dracophyllum subulatum, Leptospermum hoipolloi, L. scoparium, clubmoss (Palhinhaea cernua), and such ferns as Dicranopteris linearis, Parablechnum novae-zelandiae and Pteridium esculentum. Although Kunzea tenuicaulis is most often associated with  geothermally heated ground it can grow on the margins of these on quiescent cooler ground.

The roots of Kunzea tenuicaulis are one of the key hosts of a Pisolithus thermaceus (Pisolithaceae) an endemic mycorrhizal fungus (Lebel et al. 2018).

Kunzea tenuicaulis is usually the dominant woody species within surface expressions of geothermal fields. It is also capable of rapidly colonising newly created geothermal fields, for example, Karapiti a geothermal field greatly expanded by the abstraction of geothermally heated water for the nearby Wairakei Power Station in the 1950, provided critical fresh habitat for the species to colonise from hitherto much smaller populations confined to a few active vents. 

Within these geothermal fields the species is not seriously threatened as most of the fields are protected as reserves and even if privately owned are sufficiently active as to prevent their utilisation for other purposes. Some geothermal fields have suffered from weed encroachment and lowered water levels due to abstraction of heated water for power and amenity purposes but these activities have not seriously impacted on the Kunzea.

The species was listed as “Threatened / Nationally Endangered” qualified “DP [Data Poor]” and “RR [Range Restricted]” by de Lange et al. (2018) based on the belief that the species was placed at severe risk from myrtle rust disease caused by the exotic rust Austropuccinia psidii. Since then, there has as yet been no field evidence that this rust is impacting on the Kunzea (though inoculation trials of cultivated plants show K. tenuicaulis is susceptible) therefore, de Lange et al. (2024) changed the threat status to “At Risk / Naturally Uncommon” qualified “RR [Range Restricted]” an assessment that could change if Austropuccinia starts impacting wild populations.

This species is occasionally seen in cultivation and sometimes sold by specialist native plant nurseries.

The geothermal fields of the Taupo Volcanic Zone are well known, and many are protected as Scenic Reserves, or associated with power stations or public amenities that maintain the habitat Kunzea tenuicaulis requires. 

At this stage the impact of Austropuccinia psidii on natural populations of Kunzea tenuicaulis is unknown though experimental trials suggest that this rust will eventually kill not only seedlings and saplings but mature adults. Therefore, as the rust increases its range and dominance in Aotearoa / New Zealand the loss of host plants and shift to other members of the Myrtaceae not yet infected or sparingly so 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 ineffective. The seed of Kunzea 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 cultivated 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.