Flowering Plants

Flowering plants (botanists call them angiosperms) are the largest, most varied and most successful group of plants on Earth. Around 9 out of every 10 plant species alive today are flowering plants, including almost every garden flower, every grass, every herb and almost every tree you can think of (oak, apple, eucalyptus). They are the youngest of the main plant groups, only appearing around 140 million years ago, but they completely transformed life on land.

  • Speciesapprox. 350,000Roughly 90% of all plant species
  • First appearedapprox. 140 million years agoIn the early Cretaceous
  • Smallest flowerWolffiaLess than 1 mm across
  • Biggest flowerRafflesiaUp to 1 metre across, smells like rotten meat
  • Most speciesOrchidsapprox. 28,000, more than any other plant family
  • Key featureSeeds inside fruitProtected and easier to disperse

What makes a flowering plant?

Two big features set flowering plants apart from other plants:

  • Flowers: specialised reproductive structures that house the male and female parts in one place, often with attractive petals and scent to draw in pollinators.
  • Fruits: the seed is enclosed inside a protective fruit (the word angiosperm literally means "seed in a vessel"). The fruit can be sweet to attract animal dispersers, hard to protect the seed, or built to fly, float or stick.

These two features made flowering plants far more efficient at reproducing than the older conifers and ferns. They could produce many seeds quickly, protect them well, and recruit animals to spread them. Once they evolved, they spread fast.

The takeover of the world

Flowering plants first appeared around 140 million years ago, in the middle of the age of dinosaurs. Before that, almost all plants were ferns, conifers, cycads and similar non-flowering kinds. Within about 30 million years, flowering plants had spread from a handful of species into the dominant plant group on every continent. By 100 million years ago, the world's forests looked broadly like modern forests, with magnolias, laurels and many other recognisable plants. By 65 million years ago, when the dinosaurs died out, flowering plants were already the rulers of the plant world.

The huge variety of flowering plants

Flowering plants come in an enormous range of shapes and sizes. Almost everything green you can think of (with a few exceptions like pine trees, ferns and mosses) is a flowering plant. The big groups include:

  • Grasses: from lawn grass to bamboo to wheat, rice and maize. The most important group for human food.
  • Trees and shrubs: oak, ash, apple, eucalyptus, rose, willow.
  • Garden flowers: roses, daffodils, tulips, sunflowers.
  • Vegetables and fruits: tomatoes, beans, lettuces, apples, strawberries.
  • Cacti and succulents: adapted to dry places.
  • Orchids: the biggest family, with around 28,000 species, often with beautiful or weird flowers.

Two main types: monocots and dicots

Botanists split flowering plants into two big groups based on how their seeds sprout.

  • Monocots (about 60,000 species) have a seed with just ONE seed leaf inside, long thin leaves with parallel veins, and flower parts in threes. Grasses, lilies, irises and palms are monocots.
  • Dicots (about 175,000 species) have seeds with TWO seed leaves, broader leaves with branching veins, and flower parts in fours or fives. Most familiar trees, most garden flowers and most vegetables are dicots.
Fact The biggest single flower in the world is the Rafflesia arnoldii of the rainforests of Southeast Asia. A single Rafflesia flower can be over 1 metre across and weigh nearly 10 kg. It has no leaves, no stem and no roots: it lives as a parasite inside the roots of other plants, and only the gigantic blood-red flower ever appears above ground. It also smells exactly like rotting meat, to attract carrion-feeding flies which act as its pollinators.

Why flowering plants are so successful

Several features explain why flowering plants overtook all other plants.

  • Faster reproduction: angiosperms can flower, set seed and disperse it all in a single year (or even a few weeks). Conifers usually take much longer.
  • Partnerships with animals: by attracting pollinators with nectar and animal dispersers with fruit, flowering plants get free transport for their pollen and seeds.
  • Variety of strategies: angiosperms come in almost every shape and size, allowing them to fill every available niche.
  • Better water transport: their internal plumbing (xylem with special wide cells called vessels) moves water more efficiently than conifer plumbing.
Did you know? Almost everything you eat is from a flowering plant. The few exceptions include the seeds of conifers (pine nuts) and some seaweeds. Even when you eat a fish or steak, that animal almost certainly ate flowering plants at some point in its food chain. So in a very real sense, flowering plants feed the entire planet.
Deeper dive: Darwin's "abominable mystery"

Charles Darwin, the famous biologist who developed the theory of natural selection, was deeply puzzled by flowering plants. In an 1879 letter to a fellow botanist he called the sudden appearance of angiosperms in the fossil record an "abominable mystery". The mystery was this: the fossil record shows flowering plants appearing roughly 140 million years ago and then exploding to dominate the world within a few tens of millions of years. There was no obvious gradual fossil trail of intermediates from older plant groups, the kind of evidence Darwin's theory of slow change predicted.

For most of the 20th century the mystery remained unsolved. But over the last few decades, fossil hunters have discovered new, older flowering plant fossils, including some over 145 million years old. Genetic studies have also revealed the closest living relatives of the angiosperms (a strange small group called the Amborellales, found today on the islands of New Caledonia). Together these have helped trace the evolution of flowers back into the late Jurassic, partly resolving Darwin's puzzle.

Why flowering plants then took over so quickly is still partly mysterious. Most current theories focus on their fast life cycle, their partnership with pollinating insects (which were also evolving rapidly), and their efficient water transport. Whatever the exact reason, flowering plants are one of the great evolutionary success stories on Earth.

For how flowering plants reproduce, see pollination and plant life cycle. For the biggest examples, see trees.