Flowering plant life cycles
The flowers and fruit of flowering plants come and go as part of their life cycle. Some flowering plants don’t even have stems and leaves all the time. The fruit and vegetables we eat come from different parts of the life cycle of various plants, such as roots, stems, leaves, flowers, fruit and seeds. There is a good botany lesson to be found in food on our plate, which may include a few surprises. For example, if it has seeds in it, to a botanist it is a fruit – that includes tomato, pumpkin and cucumber.
Seeds and new plants
Seeds of a karamū (Coprosma robusta) have fallen on the ground beneath the tree. Some have germinated and started to grow new plants.
Gardeners need to know about plant life cycles so they can have food crops and colourful gardens all year round. Farmers and fruit growers need to know about plant life cycles so that they can predict when their crops will be ready.
Flowering plants all go through the same basic stages of a life cycle.
New plant grows from seed
When a seed comes to rest in conditions suited to its germination, it breaks open and the embryo inside starts to grow.
Roots grow down to anchor the plant in the ground. Roots also take up water and nutrients and store food.
A shoot grows skyward and develops into a stem that carries water and nutrients from the roots to the rest of the plant. The stem also supports leaves so they can collect sunlight.
Leaves capture sunlight to make food for the plant through the process of photosynthesis.
Adult plant produces flowers
When the plant matures and is ready to reproduce, it develops flowers. Flowers are special structures involved in sexual reproduction, which includes pollination and fertilisation.
Pollination
Pollination is the process by which pollen is carried (by wind or animals) from the male part of a flower (the anther) to the female part (the stigma) of another flower. The pollen then moves from the stigma to the female ovules.
Kiwifruit flowers
Kiwifruit have male and female flowers on separate vines. Female flowers have no nectar but use fake pollen to attract pollinating insects.
Fertilisation
Pollen has male gametes containing half the normal chromosomes for that plant. After pollination, these gametes move to the ovule, where they combine with female gametes, which contain half the quota of chromosomes for its plant. This process is called fertilisation.
From kōwhai flower to fruit
After fertilisation, the kōwhai petals fall off and the ovary grows longer. Each ovule in the ovary that gets fertilised produces a seed. Each ‘lump’ in the fruit pod is a seed.
Seeds and fruit
After fertilisation, a combined cell grows into an embryo within a seed formed by the ovule. Seeds are what a plant uses to spread new plants into new places. Each seed contains a tiny plant called an embryo, which has root, stem and leaf parts ready to grow into a new plant when conditions are right.
Bean seed embryo
After fertilisation, a tiny plant called an embryo is formed inside a seed. The seed protects the embryo and stores food for it.
Another part of the flower (the ovary) grows to form fruit, which protects the seeds and helps them spread away from the parent plant to continue the cycle.
Vegetative reproduction
New plants from a rhizome
Vegetative reproduction – three new plants growing up from underground rhizome of New Zealand native iris Libertia sp. The parent is the larger plant in the background on the left.
As well as sexual reproduction making seeds, new plants are sometimes made by asexual vegetative reproduction. These new plants have exactly the same genes as the parent. Some plants have stems called stolons that grow out sideways above the soil, and new plants grow up along them. Other plants send out underground stems called rhizomes, which form new plants at a distance from the parent. Tubers (for example, potatoes) and bulbs (for example, onions) are also special underground structures that can grow into new plants.
Length of life cycle
Flowering plants all go through the same stages of a life cycle, but the length of time they take varies a lot between species. Some plants go though their complete cycle in a few weeks – others take many years.
Annuals are plants that grow from a seed, then flower and make new seeds, then die, all in less than a year. Some go through this cycle more than once in a year.
Biennials are plants that take 2 years to go through their life cycle. They grow from a seed, then rest over winter. In spring, they produce flowers, set seeds and die. New plants grow from the seeds.
Perennials are plants that live for 3 or more years. Some, such as trees, flower and set seeds every year for many years. Some others have stems and leaves that die away over winter but the plant continues to live underground. In the spring, new stems grow, which later bear flowers.
Swan plant – a perennial
A swan plant is a perennial. It can live for many years. Each pod contains many seeds.
Did you know that the life cycle of ferns is different from other land plants as both the gametophyte and the sporophyte phases are free living, find out more in this interactive on the fern life cycle.
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