Plants need animals to survive
Without the plants there would be no animals on land
A world without plants? Many can hardly imagine that. If you don't want to encounter trees, bushes, ferns or at least mosses, you have to go to the desert, high mountains or Antarctica.
We are usually surrounded by plants, even in the concrete canyons of large cities the undergrowth grows rampant. And: without plants, no animals could live on land. They need plants for food - just like humans.
From the water to the land
There was a time when plants only existed in water. Life on land was too inhospitable for them: in order to survive here, plants have to be able to withstand dry periods. Anyone who has ever seen algae washed ashore knows that they have no protection against drying out.
But life on land also offers plants advantages, write the authors of the standard work biology by Neil A. Campbell and Jane B. Reece, which is published by Pearson. The land plants use the sun's rays without them having been previously absorbed by the water or plankton. There is more carbon dioxide in the atmosphere - which is what plants need to survive. In addition, at least initially, there were hardly any herbivores or pathogens on land.
Adjust for a life on dry land
Algae that lived in shallow waters close to banks were probably the first plants to have made the leap onto land. Low water levels forced them to adapt to the drought: if the water withdrew, the algae remained on the land.
The algae that coped best with it had the greatest chance of survival. Today they are considered to be the ancestors of land plants. Researchers therefore assume that certain types of green algae are the closest relatives of the land plants that are still alive today.
The evolution of land plants began about 475 million years ago. At least the remnants of spores were found that originate from this time and can with some certainty be assigned to the land plants. The assignment of spores that researchers found in Oman in 2003 was even clearer. Scientists dated the find around 470 million years ago. The spores were encased in a layer of wax that resembles that of land plants living today: the cuticle.
Renew yourself for country life
The cuticle is one of the most important new developments in land plants. It is formed on the parts that point upwards, i.e. towards the sky. The cuticle is supposed to prevent the plant from losing too much water.
It also protects the plants from microorganisms. Other innovations that have developed in the course of evolution are leaves, roots and pigments that protect them from UV radiation.
The land plants transport water and nutrients via the conductive tissue. The supporting fabric makes the plants stable and allows them to defy gravity. The specialized reproductive organs and the epidermal structures that enable gas exchange with the atmosphere are also innovative.
The moss plants are considered to be the oldest line of development among land plants. After them, the vascular plants, to which the ferns and seed plants belong, developed about 425 to 400 million years ago. Researchers have found fossils from this period.
Scientists believe that the first tree-shaped species finally developed around 370 million years ago. Even in the tropical forests of the Carboniferous, such plants are said to have reached an impressive size of up to 40 meters.
Insects help plants spread
The most successful plants of all emerged from the seed plants: the flowering plants (or flowering plants). They originated about 140 million years ago. The flowering plants show the greatest diversity: there are 250,000 species of them.
For comparison: Of the four groups of the naked species (e.g. the cycads, the ginkgo, the conifers and the gnetales) there are only around 840 species. One of the recipe for success of flowering plants: They use animals to pollinate each other.
In doing so, they have overcome a problem faced by plants that are firmly rooted in the soil: they exchange germ cells without moving - reproduction for the lazy.
The flowering plants attract insects with special smells and reward them for their courier services with nutritious nectar. It's good business for both sides. How this works can be seen in every spring meadow, where bees or bumblebees hurry from flower to flower.
Species diversity is growing, especially in cities
Overall, there is an enormous variety of land plants today. They are divided into nine sub-divisions. There should be between 380,000 and 500,000 recorded plant species. However: one in five of them is threatened with extinction.
The main responsibility for this is the human being, who is pushing the wilderness back further and further. In the fields in particular, farmers consciously limit biodiversity. After all, only what the farmer wants to harvest should grow here.
Species diversity is growing especially where many do not expect it: in the cities. There are up to 600 plant species per square kilometer. Flowering and other vascular plants in the urban environment are particularly diverse, whereas mosses, lichens and fungi tend not. And the rule of thumb applies: the bigger a city, the more plant species there are.
Author: Claudia Füßler
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