Auckland Museum's experts begin a five-part series on our natural surroundings. Today: plants
KEY POINTS:
Animals, including humans, depend on plants for the air we breathe - and thankfully plants are all around us.
Living plant groups, from the most advanced to the most primitive are: the flowering plants, conifers, ferns, bryophytes (mosses and liverworts), algae (seaweeds: green, brown and reds) and the lichens (which are a mix of a fungus and an alga growing together). New Zealand is well represented in all plant groups, with 80 per cent of the 2400 flowering plant species endemic to New Zealand.
On the Galapagos Islands, Charles Darwin was fascinated by the sunflower's relatives - several of them are 10m-tall trees. This is an example of adaptive radiation (something gradually changing over time). A single sunflower reached the island group from the South American mainland and then underwent adaptive radiation to form trees in the humid upland zone and shrubs in the arid areas. This plant story equals Darwin's well-known Galapagos finch adaptive radiation example, but isn't so well known. Look for the pressed Scalesia specimens collected by Darwin himself if you go to the museum's Darwin exhibition.
OUR SEARCH
We're looking for a native tree and two shrubs, all found near the coast.
The first is pohutukawa (Metro-sideros excelsa), the well-loved native tree which at this time of the year may be covered in red flowers.
The colour is from the stalks of the stamens and not the petals, which are tiny. This red colour attracts its bird pollinators, which are usually tui, capsules are formed which are packed with tiny seeds which are released to the wind in the autumn to disperse. Look at both sides of the leaves. Notice the whitish underside? This is actually a covering of fine hairs (use a hand lens if you can).
The second is a shrub, which may be harder to spot, but is frequent near the coast: kawakawa (Macropiper excelsum).
The stems are often dark, zigzag-shaped and the joints are swollen. The flowers are tiny and arranged in erect spikes, male and female flowers are on separate plants. The leaves are diagnostic (heart-shaped) with the veins radiating from the bottom, and it usually has holes in the leaves caused by a small green native caterpillar.
The third is a shrub or small tree and occurs only near the coast: houpara or five-finger (Pseudopanax lessonii), which is often "three-fingered". The compound leaves are thick and leathery, with each leaf made up of three to five leaflets; the base of the leaf stalk wraps around the stem.
The drab-coloured flowers are in groups of umbels, male and female flowers are on separate plants.
THEIR PAST
The pollen of the pohutukawa genus, Metrosideros, first occurred in New Zealand about 56 million years ago.
A DNA study at Auckland University of the 50 Metrosideros species concluded that the genus originated in New Zealand (southern rata being the oldest), spread early on to New Caledonia and only quite recently (Pleistocene) spread as far as Hawaii. Their tiny seed blows in the wind.
THEIR PRESENT
The three chosen plants are generally common along the coasts of northern New Zealand.
THEIR USE
When chewed, kawakawa leaves are mildly peppery tasting. Maori had many uses for the leaves, including chewing to relieve toothache, as antiseptic for cuts and wounds, and as an insecticide by burning green foliage which emits bitter smoke.
THEIR FUTURE
We have lost considerable coastal habitats already due to development, but thanks to the Auckland Regional Council the Auckland region now has a wonderful series of protected coastal habitats. Many plants are selectively eaten by possums, and pohutukawa is one that is top of their menu.
Possums can eventually kill large trees by repeatedly eating all the new foliage.
Swards of kikuyu or buffalo grasses often prove too thick for the tiny pohutukawa seedlings to penetrate and these large trees are unable to regenerate.
YOUR DISCOVERY
Leaves can easily be made into specimens by pressing them between pages of newspaper and changing the newspaper until they are dry. Darwin would have dried his plant specimens in a similar way.
Compare your pressed leaves with ones from different species to find differences like size, shape, colour, smell, teeth along the margins, hairs, gland-dotted (hold up to light and look for pale tiny spots).
Compare them with illustrations (e.g. Trees and Shrubs of NZ, Poole & Adams; The Native Trees of NZ, Salmon; A Guide to the Identification of New Zealand Coastal Plants, Crowe) to discover what you have collected.*
* Reference: Illustrations by Alan Esler from Wild Plants in Auckland, published by Auckland University Press.
