It is endemic to New Zealand and found throughout the country from sea level up to about 750 m in lowland to montane shrublands and forests.

[6] One of the theories about this curious change of appearance is that the young plant had to protect itself against browsing by the moa, a group of giant flightless birds that once roamed New Zealand's bush.

A closely related Chatham Island species, which evolved in the absence of moa, did not display these changes.

It is similar to P. crassifolius except the leaves are more abundant and severely toothed, resembling remotely a bandsaw blade.

Seedling leaves are smaller and thinner compared to the following growth stages, but they gradually become longer as the plant grows out from the leaf litter, starting from cotyledon.

[18] At this life stage, the top of the tree has branched and the juvenile leaves have fallen off, producing a rounded head with a naked stem.

[12] The tiny, 4 mm diameter, pale yellow to green[11] flowers are clustered in large terminal umbels, 30 cm across.

[38][39] Another moth species, Izatha blepharidota, will also take this plant as a host, with its larvae successfully reared and feeding on the dead branches of P.

Weevil species from the family Curculionidae and Belidae have larvae that live in dead, or dying, woody parts of P. crassifolius, including Dendrotrupes vestitus, Ectopsis ferrugalis, Platypus apicalis, Scolopterus penicillatus, Stephanorhynchus curvipes,[42] Psepholax simplex, Psepholax mediocris, Psepholax crassicornis, Mesoreda sulcifrons, Crisius semifuscus, Clypeolus pascoei,[43] Phronira osculans,[44] Dendrotrupes costiceps[45] and Aralius wollastoni.

[46] Two longhorn beetle species, Tetrorea cilipes and Hexatricha pulverulenta from the family Cerambycidae, have larvae that tunnel in the woody parts of trees and are believed to use P. crassifolius as a host.

Notably, Trioza panacis, also known as the lancewood psyllid, will feed on the leaves of P. crassifolius and a few other Pseudopanax species.

[53] Pseudopanax crassifolius leaves are palatable and preferred by mammals introduced to New Zealand, such as cattle,[54] deer, brushtailed possums, and feral goats.

[33][55][56] The leaves of a mature P. crassifolius tree are known to have a higher nutritive value compared to its juvenile form, which may make them more appealing to these mammals.

[62] The heteroblastic nature of this species has resulted in up to seven theories as to why it has evolved such distinct seedling, juvenile, and adult forms.

[8] One theory is that the heteroblasty of P. crassifolius evolved as a defensive adaptation to prevent and deter moa predation.

[7][63] The brown, mottled P. crassifolius seedling camouflages against leaf litter, which may have made it harder for moa to detect.

[7] Once the tree grows too tall to blend in with the leaf litter, researchers believe that the long, rigid juvenile leaves with teeth along the margin might deter moa browsing because they would be difficult to swallow.

[7] The prominent midrib of the juvenile leaf allows it to be 13 times stronger than adult leaves, which would have made it more resistant to breakage by moa.

Another theory about the heteroblasty of P. crassifolius is that it evolved due to varying light intensities that the plant experiences as it grows from below to above the forest canopy.

[9] As a juvenile, P. crassifolius often occurs as a partially shaded subcanopy tree before it eventually grows above the canopy as an adult.

The deflexed orientation of its juvenile leaves optimises capture of low-intensity light received in the subcanopy environment.

[65] As P. crassifolius grows, it enters a high-light-intensity environment above the canopy, allowing it to produce large but expensive leaves as an adult.

[66] Pseudopanax crassifolius is a popular plant in urban design not only for its iconic and charismatic appearance but also for its ecological benefits.

[8] Due to its flexibility, the trunk of a young P. crassifolius could be twisted and used as a tokotoko (ceremonial walking stick).

[8] Māori thought that a flowering P. crassifolius indicated that birds would be abundant the following year because they would be attracted to the ripened fruit.