New Zealand plants are unique! New Zealand has some of the oldest primeval forests in the world, the largest type of moss and some of the largest tree ferns found anywhere. Many of the species are very similar to those growing on Earth in the time of the dinosaurs – and even earlier.
Aotearoa separated from Gondwanaland approximately 85 million years ago. The separation from Australia left New Zealand at least 2,000 km away 55 million years ago. This isolation from other land masses meant that, until humans arrived, plants were not replaced or competed with by other species from elsewhere. They continued to evolve alone – in this unique environment.
Many plant varieties are related to plants found elsewhere – both in the northern and southern hemispheres. Fossil records also show that many of New Zealand’s plants are similar to those that were living on Gondwanaland.
However, our indigenous flora and fauna have also had time to evolve into unique species: 82% of New Zealand plants are endemic – they are not found anywhere else in the world.
Geological processes such as tectonic activity, erosion and glaciation as well as climate change and sea level changes have altered the coastline of New Zealand in the past. As a result, over millions of years, New Zealand has been a series of islands, a larger landmass, largely underwater or under ice.
The changes to the land forced a process called speciation: animals and plants with useful adaptations survived. Eventually, these animals and plants become so different from their ancestors that they were no longer able to reproduce with the ancestral species. They had become new species.
Aotearoa New Zealand also has many examples of regional endemism – where animal or plant varieties are found only in restricted locations.
Some specific adaptations of New Zealand plants
Many native shrubs have a characteristic growth form called divarication. This is where the plant grows in a tangled way, with interlaced stems and small leaves. There are several ideas about why this is useful, but the dominant theory is that divarication may be a protective mechanism. The leaves are tucked inside and therefore less accessible for browsing animals and less prone to damage from frost or snow.
Many flowers are small and white. New Zealand has a more limited range of pollinators compared to the rest of the world. Plants have evolved with animals, and the flowers have become specifically adapted to particular pollinators. Many of our pollinators are moths, small native bees, lizards and crawling insects that are not attracted by colour but by scent – so having showy flowers is unnecessary.
Most trees are evergreen. New Zealand did not undergo the extreme ice ages of the northern hemisphere, and as a result, not many of our trees are cold tolerant. They don’t have the protective adaptation of losing leaves in the winter as many northern hemisphere trees do. Only 11 species of New Zealand plants are deciduous – losing their leaves over winter.
Many of our trees are dioecious. This means they have flowers on separate male and female trees. A much higher proportion (12–13%) of New Zealand tree species are dioecious compared with other parts of the world (less than 5% in the UK). There is increased possibility of genetic variation carried in the seeds of dioecious plants. Genetic variability provides more likelihood of survival in a changing environment. The disadvantage of having separate male and female trees is that, if they are too far apart, it is more difficult for the pollen to be carried from the male to the female, reducing the likelihood of seeds forming.
Many of our plants are highly variable in their form. This often makes identification difficult. Some have slightly different forms depending on the environment they are growing in – this is called heterophylly. Hybridism is also common – where plants of different species in a family cross-pollinate, creating new varieties. Many New Zealand plant families such as the Veronica genus (formerly Hebe) now include many species.
Many plants have very different juvenile and adult forms. This is called heteroblasty, and the different form at each stage of the plant’s life provides an advantage, for example while it is growing.
Animals and plants evolved together within the environment, and over time, unique and finely tuned ecosystems developed in New Zealand. In many of our ecosystems, the organisms became so interdependent – relying on each other for food, habitats and life processes such as pollination – that any changes could be detrimental. These changes are easier to see with iconic species of animals but may be less obvious in the plant world. However, many of our plants are now endangered. Deforestation caused a huge reduction in habitats, as did the introduction of other organisms into the New Zealand environment.
Many introduced plant species have become weeds, which can either outcompete native plants for habitat (wilding pines) or have a direct negative impact on the plants themselves (old man’s beard). Predators and other introduced wildlife can destroy pollinators such as birds or lizards or successfully compete with them (stoats and possums) or impact negatively on the plants themselves (mice eating native seeds).
Nature of science
This article highlights the ‘Understanding science’ aspect of the Nature of science – it illustrates how scientists use evidence to create theories about why New Zealand plants are so unique.
There is a range of useful resources for further reading about native plants. These include books by authors such as Andrew Crowe, John Salmon, John Dawson and Tony Foster. Websites such as Manaaki Whenua – Landcare Research, Department of Conservation and Bushmansfriend all provide detailed information about New Zealand native plants.
The Department of Conservation has recently produced a report on our endangered plant species – New plant status report shows increased threats – and kauri has now been reclassified as a threatened species, mainly due to kauri dieback disease.