How do plants have babies?

By Becca Smithers

Plants are incredible. They can be found in dry, rocky places, they can be over 100 metres tall, they can be eaten, and most importantly they provide the oxygen in Earth’s atmosphere. Plants mostly stay in one place, so how do plants reproduce and have babies? Across the whole of the plant Kingdom, there are two methods of reproduction that plants can do: sexual and asexual.

Sexual reproduction

Sexual reproduction is when a male gamete (sex cell) and a female gamete join to create a zygote (fertilised cell). The zygote will then develop into a seed which will eventually grow into a new plant. Sexual reproduction mostly occurs in plants that produce pollen. Pollen is the male gamete and it needs to come into contact with stigma, a female part of the plant that collects pollen and transfers it down the style to the ovule (female gamete) which gets fertilised. The fertilised ovule will develop into a seed which can be picked up by the wind (e.g. dandelions, sycamore), carried on the fur of animals that brush past the plant, or the seed can be carried in a fruit (e.g. apples, blackberries). Birds and other animals eat the fruit and can help to spread the seeds of the plant one they pass through their digestive system.

The anatomy of a flower. CC-BY- SA ProFlowers.

In the above picture, you can see the stamen and pistil, both male and female parts in the same flower. The male stamen produce the pollen and the female pistil receives the pollen. Flowers with both male and female anatomy are called “perfect flowers”, but you can have flowers that only have the stamen or pistil, creating male (staminate) and female (pistillate) flowers. If these male and female flowers appear on the same plant, or if the plant has perfect flowers, then the plant is referred to as monoecious and can self-fertilise. Other plants are dioecious, meaning that male and female flowers will appear on different individual plants. This can help prevent self-fertilisation and increase the genetic diversity of the plants. Examples of monoecious plants are hazel and oak, and examples of dioecious plants include willow and holly.

How does the pollen of one plant get to another?

Pollinating plants have two methods of spreading their pollen: by the wind, or by pollinators.

Grasses are examples of plants that use the wind to spread their pollen. The wind carries the pollen and because grasses grow close together it is very likely that the pollen will land on the correct grass, but it is still a large gamble. A lot of pollen in lost by the wind so grasses and other wind pollinating plants have to produce a lot of pollen to make up for this. A lot of people suffer from hay fever when wind pollinating plants are trying to reproduce in spring, the excess pollen in the wind can cause an allergic reaction in humans!

Bee covered in pollen

Using pollinators is a safer bet of transferring pollen to the correct plant. Bees, flies, and other insects are good pollinators. They are attracted to the flowers of plants by their colour, smell, and the promise of sugary nectar. Bees will balance on a flower and use their long tongue called a proboscis to get to the nectar at the base of the flower. The nectar is there to tempt the pollinators to stay on the flower long enough to get coated in some pollen. Bees also use pollen as food in their hives so collect some in small pouches on their legs. The pollinators will fly from flower to flower and transfer the pollen as they go. If the pollen is compatible then it can fertilise the ovule.

Asexual reproduction

This type of reproduction is where a plant makes a clone of itself meaning that the new plant will have exactly the same genes as the parent plant. These clones can grow from long, horizontal stems that can either grow below or above ground. Below ground stems are called rhizomes, above ground horizontal stems are called stolons or runners. The clone plants, called plantlets, grow off these stems.

Here are two examples of plants reproducing asexually, the aloe plant and spider plant that live on my desk! The aloe plant is growing plantlets from the soil which shows there is a rhizome producing the new plants. The spider plant has a runner growing plantlets, trailing away from the parent plant.

Aloe plant (left) and spider plant (right) reproducing asexually.

Bulbs and cacti can reproduce asexually through budding where a new plant can grow off the current plant or bulb. In daffodil bulbs and other plants that come back year after year (referred to as “perennial” in gardening terms), new plantlets grow from a bud that has been asexually produced by the original bulb. This happens underground so is difficult to see. Budding in cacti is much clearer as you can see the new cacti plantlet growing from the original parent plant.

Understanding how to grow plants asexually has led to some interesting gardening techniques such as taking plant cuttings where you grow a clone plant from a cutting of the parent.

The ability to reproduce sexually and asexually gives plants a really good chance of surviving and colonising new areas. Sexual reproduction diversifies the gene pool but asexual reproduction guarantees new plants. This reproductive advantage is one reason why plants can be found in almost all environments on Earth.

 


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Posted in Biology