Scientists divide plants into two main groups depending on whether they reproduce by seeds or spores.
Plants that reproduce by seeds
Seed plants have special structures on them where male and female cells join together 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 parent plant disperses or releases the seed. If the seed lands where the conditions are right, the embryo germinates and grows into a new plant.
Scientists divide seed plants into two main groups: plants with flowers and plants with cones. They also have special names for these groups. Plants that have flowers are called angiosperms. Plants that hold their seeds in cones are called gymnosperms.
Angiosperms – seed plants with flowers
Angiosperms have flowers. The flowers 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, insects or other 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.
Gymnosperms – seed plants with cones
Gymnosperms are seed plants 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.
Plants that reproduce by spores
Ferns, mosses, liverworts and green algae are all plants that have spores. 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, usually in a damp place. An embryo is formed and a new plant grows from it. New Zealand has about 200 species of ferns and over 500 species of moss.
Nature of science
Classification helps us put order into the world around us. Scientists start with very big categories like plants and animals and continue to divide the groups based on shared characteristics – like methods of reproduction.
Take a bag of (thawed) frozen broad beans to school and hand a few to each student. Students can remove the seed coat and split the bean to reveal the embryo inside. Use magnifying glasses to examine the embryos.