Plants, also called green plants, are multicellular eukaryotes of the kingdom Plantae. They form an unranked clade Viridiplantae (Latin for green plants) that includes the flowering plants, conifers and other gymnosperms, ferns, clubmosses, hornworts, liverworts, mosses and the green algae. Green plants excludes the red and brown algae, the fungi, archaea, bacteria and animals.
Green plants have cell walls with cellulose and obtain most of their energy from sunlight via photosynthesis by primary chloroplasts, derived from endosymbiosis with cyanobacteria. Their chloroplasts contain chlorophylls a and b which gives them their green color. Some plants are parasitic and have lost the ability to produce normal amounts of chlorophyll or to photosynthesize. Plants are also characterized by sexual reproduction, modular and indeterminate growth, and an alternation of generations, although asexual reproduction is also common.
Types of Plants
Kinds of Plants
Most people will recognize most of the plants on this page. At the same time, we don't always pay too much attention to what makes some living things similar and what makes them different. It is not easy to see that an oak tree and a geranium are near relatives until you start to look closely.
The way we look at plants now has a lot to do with the work of Carl Linnaeus He was a 17th Century, Swedish scientist and he wanted to work out just how many different kinds of living thing there were.
He separated living things into plants and animals- in the same way that people had done for a very long time- but then went much further. He proposed groups and families where living organisms could be placed with their closest relatives. This was the beginning of modern scientific classification.
Classification has changed, as science has advanced but the Linnaean system is still in pretty good shape. On this page you will find the main groups of plants according to that system.
The Main Kinds of Plants
Plants without Seeds
- Algae: green, brown and red (see discussion below: 'Are algae really plants?')
- Mosses and Liverworts
- Ferns and Horsetails
Plants with Seeds
- Cycas- palm trees, for example
- Ginkgo- a living fossil
- Conifers- Spruce, Fir, Larch and so on
- Flowering plants- from Oak trees to Geraniums
Algae
Kinds of Algae: Green, Brown and Red
Green Algae
This is a very varied group of living things with many thousands of individual species. Most green algae live in water. Some live where it is very damp all the time. They hate being dried out.
If you see a pond where the water is green it will probably be because millions of tiny green algae have grown there. Each alga is invisible to the naked eye.
On a seashore, you might come across kinds of green algae that are very big indeed- the green seaweeds.
Brown Algae
Brown algae is more common in the ocean than in freshwater.
Some of the tallest plants in the world are brown algae. Giant kelp, for example, is common in shallow oceans- especially off the coast of California. It can be as tall as 250 feet!
A single-celled alga viewed through a very powerful electron microscope. This one is a sea dweller but many similar kinds live in freshwater ponds and lakes.
Are Algae Really Plants?
To a scientist, the answer is 'no'. To most people, the answer is 'yes'.
Close study suggests that algae have more in common with bacteria than plants and scientists have removed them from the Plant Kingdom
Algae photosynthesise (make food from water and carbon dioxide) as do all plants but they lack the distinctive structures of true plants like roots and leaves.
A Kelp Forest with many brown algae. Photo by Fastily
Liverworts
Liverworts are small plants that you see in damp places. They can stand being dried out a little better than algae but not much.
A common kind of liverwort is pictured below. You usually see this kind near waterfalls or in woods with a lot of rain. The picture has a high magnification. These plants are pretty small!
Liverworts are believed to have evolved soon after plants made the transition from water to the land. In this sense they are more advanced than algae.
They do not have the sophisticated vessels that transport water from roots to leaves found in more advanced plants.
A Quaking Bog
Ferns
Ferns are far better at coping with dry periods than either algae or mosses but still need very wet conditions to reproduce. This limits where they can grow. You will not find a fern in a desert!
Bracken is an especially successful kind of fern in countries with a cool, wet climate. It spreads quickly by using 'creeping rhizomes' and can cover many acres very quickly.
In Devonian times- many millions of years ago, ferns were the dominant land plant on our planet. Instead of forests of Fir trees or Oak, the forests would be made up of huge tree ferns. Later on, many familiar dinosaurs like the Triceratops would be happy to dine on ferns.
Typical fern leaf
Plants with Seeds
Seeds have an outer layer that helps protect against drying out, infection or consumption by animals
Cycads
These mostly grow in Central America, Africa, SE Asia and parts of Australia.
They are the kinds of plants you see in jungle movies- but some are popular house and garden plants. They like moisture and heat.
They can be tall and often have woody trunks. The leaves tend to be long and thin.
If you have grown up in a Northern climate, cycads can be strange plants to encounter. Quite suddenly unfamiliar and fascinating structures will grow out of a cycad in my garden, for example, and have me hunting through my books to find out exactly what is happening.
These structures are usually cones of some kind- similar to the cones that conifers produce.
Cones bear exposed seeds rather than the kinds of seeds that you find in flowering plants, which are well protected until they are released. The seeds are often pollinated by special kinds of beetle rather than bees or other insects.
Typical Cycad Cone.
Ginkgo
There is only one kind of Ginkgo in the world today- Ginkgo Biloba- and when you look at the fossils of this plant, it might be that there was only ever one kind.
Despite the lack of diversity, the Ginkgo once covered huge areas of the world. Now they are only found naturally in Central China.
Most scientists think that flowering trees outdid the Ginkgo and it gradually died out as modern trees evolved.
It is sometimes called a living fossil.
At the same time, the tree's beauty has meant that gardeners and park keepers have carefully planted many Ginkgo Biloba trees around the world.
Fall colors of a female Ginkgo Tree in Japan.
Conifers
A Spruce Forest, young Larch Cone and old Fir Cone
Conifers are close relatives of cycads. They have cones with seeds and they also have woody trunks.
The most noticeable difference is that conifers like cold, northern climates where they can form huge forests that can stretch from one side of a continent to the other.
The typical conifer shape is excellent at shedding snow. They also have many ways of coping with freezing at the cellular level.
Conifers are popular garden plants too. They grow very quickly and they are evergreen.
Flowering Plants
An Oak Tree, a geranium, an orchid and a shrub (hydrangea) in full flower
Some people think of plants and trees as very different. The truth is that trees are plants just as much as a row of lettuce or a fine rose.
Flowering plants are the most familiar kinds of plant for anyone who lives in a temperate climate (not too hot, not too cold).
The thing that makes a geranium so similar to an Oak tree is the flowers that they both produce. Flowering plants protect the female parts of the plant inside thick walls of tissue. The male parts of the plant produce pollen, and this needs to burrow its way through this tissue to produce an embryo that then develops into a seed.
Pollen can be transferred from one plant to another by wind or by insects like bees. Plants that use wind pollination usually have small, drab and inconspicuous flowers. Flowers that use insects for pollination are often big and bright so that the insects can see them from a long way off.
Flowering plants are the plants most able to cope with dry conditions. Cacti can flourish in places where there is no rain for many years at a time.
While flowering trees grow more slowly than conifers, their hard wood is more resistant to insect damage. This means they do better in warmer places
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