Plants are living things:
- They grow and die.
- They produce young.
- They are made of cells.
- They need energy, nutrients, air and water.
- They react to their environment.
Plants are different to animals partly because they get their energy from sunlight through a process called photosynthesis (although there are a few plants that don’t). Plant cells have much in common with animal cells, but they have some different structures.
There are many different kinds of plants. Just take a walk in the garden or bush to see the amazing variety. Botanists organise the plant kingdom into groups based on features found in different plants.
Plants are divided into two big groups, based on how they reproduce:
- Plants that have seeds (flowering plants and cone plants).
- Plants that have spores (ferns, mosses, liverworts and green algae
Seed plants have special structures on them (flowers or cones) where special male and female cells join through a process called fertilisation. After fertilisation, a tiny plant called an embryo is formed inside a seed. The seed protects the embryo and stores food for it. The seed is dispersed away from the parent plant, and when conditions are right, the embryo germinates and grows into a new plant.
Spore plants have a different life cycle. A parent plant sends out tiny spores containing special sets of chromosomes. These spores do not contain an embryo or food stores. Fertilisation of the spores takes place away from the parent, then an embryo is formed and a new plant grows from it.
There are two main groups of seed plants:
- Gymnosperms – plants with cones.
- Angiosperms – plants with flowers.
These seed plants do not have flowers or fruit, but their seeds are held in cones. Next time you pick up a pine cone, look for loose seeds inside. Male cones make pollen, which is carried to female cones by the wind. After the female gametes are fertilised by male gametes from the pollen, the female cones produce seeds, which are then scattered away from the plant by wind or animals.
Most gymnosperms are trees. There are about 20 native gymnosperms in New Zealand, including our tallest tree, the kahikatea (Dacrycarpus dacrydioides, white pine). Others include mataī (Prumnopitys taxifolia, black pine), tōtara (Podocarpus totara), rimu (Dacrydium cupressinum, red pine) and kauri (Agathis australis). The main tree that makes up New Zealand’s plantation forests is the exotic gymnosperm Pinus radiata
Angiosperms have flowers, which are special structures for reproduction. They contain male parts that make pollen and female parts that contain ovules. Some plants have these male and female parts in different flowers. Pollen is carried from a male part to a female part by wind or animals (a process called pollination), where it releases male gametes that fertilise the female gametes in the ovules. The ovules develop into seeds, from which new plants will grow. In most angiosperms, part of the flower develops into fruit, which protects the seeds inside them. Fruit can be soft like oranges or hard like nuts.
Flowering plants form the biggest group of seed plants, with about 300 000 species around the world – that’s 90% of the whole plant kingdom. New Zealand has about 2000 native angiosperms, and an amazing 25 000 introduced species found mainly in gardens, farms and orchards.
Flowering plants are all around us, even if sometimes we don’t recognise them as having flowers. We all know the showy flowers of native kōwhai, flax and pōhutakawa and all those lovely coloured flowers in our gardens, but the tall toetoe and the grasses in our lawns are also flowering plants.