The distinctions between Myoporum semotum and the variable M. laetum are minor, a feature of many of the arborescent Myoporum, and there is the need for further taxonomic evaluation, ideally using a robust phylogeny to help inform taxonomic decisions.

Myoporum semotum is a small tree, endemic to Aotearoa / New Zealand where it occurs on six of the islands in the Chatham Islands group, and in the Mahia Peninsula, northern Hawkes Bay, Te Ika a Maui / North Island. The population is estimated to consist of at least 6,610–7,110 mature individuals. Population trends, though unknown, have been estimated to decline by up to 30%, projected over the next 100 years. This species is only secure on small outer island Nature Reserves. It is assessed as Near Threatened.

This species is endemic to Aotearoa / New Zealand. In 2015 was discovered at one location, Mahia Peninsula, northern Hawkes Bay, Te Ika a Maui / North Island, otherwise known only from the Chatham Islands group (Rekohu / Wharekauri / Chatham, Rangihaute / Rangiauria / Pitt, Wharekaikite / Rabbit, Maung’re / Mangere, Tapuaenuku / Little Mangere and Hokorereoro / Rangatira / South East Islands). Distribution map is generalised.

No accurate population estimate for this species is known. At Mahia Peninsula one tree was found by chance in a coastal forest remnant on a remote roadside near the south-eastern end of the peninsula (iNaturalist 2023). A search for the tree in 2022 discovered that, because of the installation of a nearby rocket launch pad, the roading had been improved and roadside vegetation sprayed / cleared. The tree has been killed. Limited surveying of Mahia Peninsula has not found further plants, though Myoporum laetum is abundant there. It is unlikely that this tree was deliberately planted as Myoporum semotum is scarcely known from cultivation in Aotearoa / New Zealand and the site (at least in 2015) was very remote from urban areas. It should be noted that the identity of the Mahia tree is disputed by some botanists.

On the Chatham Islands group, Myoporum semotum is abundant on Hokorereoro / Rangatira / South East Island where it forms one of the dominant trees in the coastal forest of the northern portion of that island. The species is less common on Maung’re / Mangere which is still recovering from its deforestation for farming in the late 1800's. Only scattered specimens are known from Tapuaenuku / Little Mangere and Wharekaikite / Rabbit. On Rangihaute / Rangiauria / Pitt Island, Myoporum semotum is locally common in coastal forest (Heenan and de Lange 2011), though very few locations are secured from livestock and feral pigs (Sus scorfa) so many remnants are on the verge of collapse. On Rekohu / Wharekauri / Chatham Island the species was discovered in January 2018. It is known there from scattered stands near Cape Pattison, and isolated trees at Kaingaroa, Waiteki / Waitangi and on Motuhinahina. M. semotum is probably more widespread than this, especially along the remote and largely inaccessible coastal cliff forests of the southern tablelands.

Collectively, based on these occurrences M. semotum is presumed extinct in Te Ika a Maui / North Island, scarce on Rekohu / Wharekauri / Chatham Island (with a population of c. 500 trees), locally common but in decline on Rangihaute / Rangiauria / Pitt Island (population of c. 1,000–1,500 trees), secure and increasing its range on Hokorereoro / Rangatira / South East Island (population of c. 5,000 trees), and present on Maung’re / Mangere Island c.100 trees, but with many more planted as part of that islands restoration), Tapuaenuku / Little Mangere (unknown numbers but presumed very uncommon), and Wharekaikite / Rabbit Island (10 shrubs / trees). These estimates suggest a total population of  c. 6,610−7,110 mature trees. Undoubtedly more trees exist on Rangihaute / Rangiauria / Pitt Island, and it is probable that the species also occurs on the forested tops of Motchu Hop’ / Star Keys and large parts of Rekohu / Wharekauri / Chatham Island remain unsurveyed.

Population trends though unknown have been estimated at 10–30% projected over the next 100 years (Townsend et al. 2008, de Lange et al. 2018).

Myoporum semotum is a tree of coastal forest (Heenan and de Lange 2011). Specimens usually are the dominant tree where shrubland gives way to forest at the back of beaches, shore platforms and cliff faces. On Rangihaute and Rekohu it is also a component of forests developed over sand dunes or on uplifted shore platforms. Common co-associates include Olearia traversiorum, Coprosma chathamica, Myrsine chathamica, Pseudopanax chathamicus and the naturalised Corynocarpus laevigatus. Trees appear to be long lived (c.100–150 years – based on historic images and records), coppice readily when damaged, and layer when toppled. The fruits are bird dispersed. At Mahia Peninsula a single tree was found in a roadside forest remnant dominated by Pennantia corymbosa, Rhopalostylis sapida, Olearia rani, Kunzea robusta and Corynocarpus laevigatus.

Aside from the Mahia Peninsula occurrence, which in the absence of further finds cannot be considered further, Myoporum semotum is a Chatham Islands endemic (de Lange 2023). As with most Chatham Island plants it is likely that this species has experienced a major decline following Polynesian occupation of the islands c. 600–800 years ago, a decline which accelerated following European settlement (starting in the 1820's) and then the arrival of Māori (1830's). Determining historic loss is complicated by the presence of Myoporum laetum on Rekohu / Wharekauri / Chatham Island, as older botanical accounts merely mention ‘ngaio’ (a name which is used for both species), Myoporum semotum was only recognised as distinct in 2011, prior to which, undoubtedly there had been a major decline of the species throughout its range (possibly exceeding 80% of its former likely occurrence).

Heenan and de Lange (2011) noted Myoporum semotum as only present on Rangihaute / Rangiauria / Pitt Island and nearby islands, they considered it to have its stronghold on Rangihaute and Tapuaenuku / Little Mangere noting that it was scarce on the other islands. This situation has changed, the species is now known to be abundant on Hokorereoro / Rangatira / South East Island and it is believed scarce on Tapuaenuku (de Lange 2023). In January 2018 Myoporum semotum was discovered on Rekohu / Wharekauri / Chatham Island, in sand dune forest remnants near Cape Pattison, and it has since been found in a few other sites as single trees. On the main islands of the Chathams group Myoporum semotum is not secure, very few of the known sites are fenced from livestock and have possum (Trichosurus vulpecula) control, and some, though nominally reserved or covenanted land, and in a serious state. Livestock and feral pigs (Sus scrofa) uproot seedlings and saplings and topple trees directly though physical pressure on their trunks and indirectly by destroying the forest understory and shrub layer, causing soil desiccation, and allowing wind to blow through the forest, again causing toppling. The species is also potentially at risk from hybridization with Myoporum laetum, a species not considered indigenous to the islands (de Lange et al. 2011) that has naturalised in the northern part of Rekohu / Wharekauri / Chatham Island, and which could be confused with M. semotum. Myoporum laetum is notorious for forming hybrids with M. insulare in Aotearoa / New Zealand, so there is no reason to assume it will not with M. semotum.

The New Zealand Indigenous Vascular Threat Listing Panel have assessed Myoporum semotum at ‘At Risk / Declining’ because at many sites only mature trees are known and recruitment over most of the species’ range is an issue. Population trends though unknown have been estimated at 10–30% projected over the next three generations (Criteria ‘Declining’ A1 (S1, T1) (Townsend et al. 2008) – see also de Lange et al. (2018)). The species’ long-term security requires ongoing biosecurity to ensure the outer predator-free islands on which the species is secure remain that way.

This species is occasionally cultivated in Aotearoa / New Zealand.

Myoporum semotum is threatened by the lack of regeneration over much of its range on the larger islands, with the most populations not fenced and in serious decline. Better fencing and ongoing fence maintenance is needed, as well as wild animal control, especially of pigs and possums. There is also ignorance regarding Myoporum semotum as an indigenous tree to the islands and thus confusion with M. laetum (an issue for restoration plantings, and there is a risk trees might be accidentally felled through this confusion with M. laetum which is naturalised to the islands (de Lange et al. 2011) and a potential pest species). So good education is needed to ensure the correct species is grown and planted out. On the outer islands, all of which are nature reserves, it is imperative that biosecurity measures currently in place are maintained. Rodent incursions will impact not only on those islands’ biota and ecological integrity but also Myoporum, as they predate fruits and seeds.

Myoporum semotum is one of the species being replanted onto Maung’re / Mangere Island as part of that island’s restoration (it is fortunate that the source for those Myoporum had been trees from that island, otherwise M. laetum may have been accidentally planted). Other restoration plantings using this species are being undertaken by Moriori (the indigenous people of the islands) at Kaingaroa Farm Station and at Manukau, and trees have been planted at Point Gap Sanctuary. Further plantings using this species should be encouraged.