Long regarded as a species of Olearia, Macrolearia chathamica belongs to an informal grouping of six taxa known as the ‘Macrocephalous’ Olearia (Drury 1968) which on further study was shown to be part of the Pleurophyllum clade but distinct from Damnamenia and Pleurophyllum (Saldivia et al. 2022), leading to the segregation of this grouping to a new endemic genus Macrolearia.

Macrolearia chathamica is a shrub or small tree, endemic to Aotearoa / New Zealand where it occurs on five of the islands in the Chatham Islands group. It is estimated that there are about 20,000 individuals in situ. There is a suspected decline in population of up to 70% over three generations. This is mainly due to livestock grazing, drought and invasive species. It is assessed as Endangered.

This species is endemic to Aotearoa / New Zealand where it occurs on the Chatham Islands group, from Rēkohu / Wharekauri / Chatham, Rangihaute / Rangatira / Pitt, Maung’re / Mangere, Tapuaenuku / Little Mangere and Hokorereoro / Rangatira / South East Island.

No accurate population assessment has been undertaken. It is estimated that there are c.20,000 Macrolearia chathamica mature individuals (de Lange et al. 2018). These are spread over all of the main vegetated islands of the Chathams group. The largest subpopulations are found on Rangihaute / Rangiauria / Pitt Island (where c.10,000 mature specimens may reside). Maung’re / Mangere Island and Hokorereoro / Rangatira / South East Island as Nature Reserves have the most secure populations, and both are actively regenerating as those islands recover from past attempted farming. On Rekohu / Wharekauri / Chatham Island the species has been extirpated from two-thirds of the island, such that it is only known as naturally occurring plants along the coastline of the southern tablelands from the mouth of the Tuku River east to Rangaika Scenic Reserve and covenanted land nearby. In this area c. 8,000 mature specimens are thought to exist. Where land has been fenced to exclude livestock, regeneration is rapid provided there are nearby seed sources. Regeneration is also common where tracks have been pushed through coastal forest or where there has been some feral pig (Sus scrofa) damage to the vegetation. However, excessive pig rooting will kill seedlings, saplings, and adults.

With available knowledge the species is predicted to experience a population decline of 50–70% over three generations (1900–2120). This is due to historical loss of subpopulations at certain localities and the decline is still continuing despite regeneration. 

Macrolearia chathamica is shrub or small tree (up to 8 m tall but usually much less) of coastal locations where it grows on cliffs, rubble slopes, and the forest that has colonised the cliff tops, ridgelines, outcrops, and other similar exposed habitats (de Lange 2023). In forested habitats it often forms a narrow strip along the seaward side, the trees growing so close together as to exclude other associated woody shrubs and trees. In these situations, co-associates usually include Dracophyllum arboreum, Myrsine chathamica and in places Veronica barkeri. In a few places, Macrolearia chathamica may grow well inland (usually on exposed ridgelines and outcrops) but also on cliff faces and steep banks bordering the inland peat lakes (de Lange 2023), In these places it is a minor component of Dracophyllum / Myrsine / Coprosma forest. In a few places it may abut restiad bog and in these situations its range overlaps with Macrolearia semidentata, which results in limited hybridization. Hybrids are, however, scarce.

Macrolearia chathamica appears to be longer-lived than M. semidentata, perhaps as long as 100 years based on historic image and field records. However, like that species it seems to need disturbance to regenerate, as seedlings are usually found on recently exposed ground, slip scars, rubble slopes or where canopy gaps have been caused by tree fall. Despite its proclivity for coastal situations and tolerance of salt spray, the species seems to require abundant moisture, though it prefers free-draining substrates and avoids water logged soils. Moisture may be obtained from ground water, seepages and water ways or water that has been trapped in the foliage from sea fogs. Plants dislike drought and are prone to sudden collapse when water-stressed in the wild and in cultivation (Metcalf 1972, as Olearia chathamica).

The main threats to Macrolearia chathamica are unrestricted stock access. Livestock readily eat seedlings and young plants, and damage the trunks and roots of mature trees, so weakening and eventually killing them. Excessive pig rooting also destroys plants. During droughts plant are prone to sudden collapse and are vulnerable to fires. The species went extinct from the northern two thirds of Rekohu / Wharekauri / Chatham Island sometime over the last 120 years (it was already scarce in this region when Cockayne did his surveys of the island groups vegetation (Cockayne 1902)) as a consequence of vegetation clearance and stock browsing – notably attempts to re-establish it in this area have met with failure. Fencing of remnants results in spectacular regeneration. However, fences require considerable maintenance due to the coastal habitats the species occupies, fence wire and mesh rusting faster in these areas. The largest population of this species, on Rangihaute / Rangiauria / Pitt Island is mostly unfenced and has unrestricted stock and pig access, and now comprises mostly moribund adults with little regeneration. Possums (Trichosurus vulpecula) browse M. chathamica but how severely is unknown.

This species is very uncommon in cultivation in Aotearoa / New Zealand. Cultivated plants of this genus are prone to sudden collapse (Metcalf 1972 – treated there as Olearia). Occasionally grown in Aotearoa / New Zealand Botanic Gardens.

The species is considered secure only on the Nature Reserves Maung’re / Mangere and Hokorereoro / Rangatira / South East Islands. On the larger islands some populations are protected within the Tuku Nature Reserve, Rangaika Scenic Reserve, at Canister Cover and on nearby kawenata / covenants such as Sweetwater. However, the main populations in these areas are on private land, and at nearly all of the known sites pigs and feral livestock are a constant threat.

Fencing to exclude livestock and animal control within fenced sites will secure the species. This is already well known from past management efforts by the New Zealand Department of Conservation. However, regular fence maintenance and animal control is essential, and to date this has been inconsistent. It is hoped that the initiatives of the Predator Free 2050 team on the islands may help restore these management requirements.

Although fickle in cultivation, more effort should be made to grow the species for island restoration projects.

An accurate census of the species is needed to better determine population size and decline rates. Long-term monitoring at key sites (protected and not) is needed.

Macrolearia chathamica was assessed as ‘Threatened / Nationally Vulnerable’ (de Lange et al. 2018, de Lange 2023) on the basis of the assumed to be small population (Criterion D1) and predicted decline rate of 30–70%.