Scrambling along a rough mountain trail, I am surrounded by strange trees clinging precariously to the slopes. With their etched and contorted trunks topped by jagged fronds and gaudy orange cones, these are the most bizarre trees I have ever seen.

This is the sacred cycad forest of the Rain Queen, the hereditary ruler of the Balobedu people of Limpopo province in South Africa. Cycads grow here more abundantly than anywhere else on Earth, and the queen is said to use her magical powers to protect them. These strange plants need all the help they can get right now, magical or otherwise, to ward off the unscrupulous collectors that are plundering them. But long before the human threat arrived, the cycads faced a challenge of an altogether greater magnitude.

Step back 150 million years and you would have seen an incredible profusion of cycads, along with their relatives the conifers, in myriad shapes and sizes all over the world. Both are part of an ancient plant group called the gymnosperms that has its origins 370 million years ago. For 250 million years, the gymnosperms were kings of the castle, but their reign is long over. Many lineages have gone extinct and the survivors have been largely sidelined. Conifers remain dominant only in harsh northern forests and other marginal habitats, while the cycads have fared even worse. The gymnosperms' fall coincided with the spectacular rise of a new force - the flowering plants.

Natural colonisers

The angiosperms, as flowering plants are known, dominate the world's flora and provide food and shelter for innumerable creatures, including ourselves. They are nature's great colonisers - adaptable, persistent and enormously diverse. From minuscule duckweeds to mighty baobab trees, there are 300,000 species of angiosperm compared with just 1000 gymnosperms. Yet it is the flowering plants that are the newcomers. They rose from obscurity to conquer the world's prime real estate during the Cretaceous period, between 145 and 65 million years ago.

The rise of the angiosperms has puzzled biologists for more than a century. In 1879, Charles Darwin famously described it as an "abominable mystery". Recent research, however, has started to fill in many of the blanks. It turns out that the floral takeover wasn't quite as sudden as previously thought, but once it got going it took off with an almightly bang.

As recently as 30 years ago, fossil flowers were virtually unknown. Back then, the ancestral flowering plant was assumed to have lived around 100 million years ago and been big-bloomed, like a magnolia, as such plants were considered to be the most primitive living angiosperms.

That all began to change in 1981, when a huge cache of 83-million-year-old fossil flowers was pulled out of a clay pit at ร…sen in Sweden by Else Marie Friis, then of Bedford College in London (now at the Swedish Museum of Natural History in Stockholm). These immediately suggested why fossil flowers had appeared so thin on the ground: they were nowhere near the size of a magnolia.

The secret of success for Friis and her team was the method they used. "The new approach was to bulk sieve soft sediment. What came floating out were thousands of tiny, beautifully preserved fossil flowers," says botanist Peter Crane of the University of Chicago. All of a sudden, here were the flowers everyone had been searching for, and lots of them. Measuring just 1 or 2 millimetres in size, they include relatives of walnuts, plane trees and saxifrages that had been turned to charcoal in a wildfire (Nature, vol 291, p 485). The finds inspired other teams to think small, and many more tiny flowers, up to 112 million years old, have since been discovered from sites around the world.

These are by no means the oldest fossil flowers, though. That honour falls to those of a 125-million-year-old pond weed found in the Yixian deposits in north-east China in 1998. The area is most famous for its feathered dinosaurs, but its flora is turning out to be every bit as important. Archaefructus is exceptional in having flowers, fruits, leaves, stems and roots all on the same fossil slab (Science, vol 282, p 1692).

The flowers of this pond-dweller would have been above the water - though you would hardly recognise them as flowers. "Archaefructus had not yet evolved the ornate floral organs that we associate with flowers," says co-discoverer David Dilcher of the Florida Museum of Natural History in Gainesville. Even so, its small, dowdy reproductive organs clearly qualify Archaefructus as angiosperm, because the female parts are entirely enclosed within a protective fleshy structure called the carpel. This "closed" carpel is one of the defining features of flowering plants.

It is also part of the evolutionary innovation in sexual reproduction that gave angiosperms the edge over their rivals. For reproduction to take place in a flower, sperm cells from pollen have to burrow through the carpel to reach the egg. Once inside, a process known as double fertilisation occurs, with one sperm fertilising the egg and another fertilising a neighbouring cell that will develop into a food supply for the embryo. Double fertilisation is unique to angiosperms and it gave them two important evolutionary advantages. First, embryo and food supply start growing at the same time, which makes angiosperms faster breeders than gymnosperms. Second, the nourishing tissue is only produced if fertilisation has occurred, which means precious resources are conserved.

By contrast, gymnosperm seeds, such as those in a pine cone, are loaded up with nutrients before fertilisation can occur. This substantially lengthens the reproductive process and means that every seed is provisioned regardless of whether it gets fertilised or not. Flowers had a winning strategy from the outset.

Archaefructus may be the oldest fossil angiosperm, but it wasn't the first. To go further back in time, though, you have to look for more subtle types of evidence.

One of these is the pollen record. Fossil pollen is abundant in sedimentary rocks and the grains come in a variety of shapes and sizes, some of which are unique to flowering plants. The oldest unambiguous angiosperm pollen is a few precious grains from sediments in southern England that are 135 million years old (Micropalaeontology, vol 10, p 75). Though clearly angiosperm, these grains are hugely outnumbered by gymnosperm pollen. "When flowering plants first appear they are not abundant, nor diverse," says Crane. "They are also completely subservient to all of the other plants at that time." The flora of the day was dominated by conifers, cycads and their extinct relatives.

Genes provide another window on the past. In 1999, an analysis of DNA sequences from hundreds of living plant species created an angiosperm family tree. It revealed that a rare evergreen shrub with tiny cream flowers and red berries called Amborella is the most primitive living angiosperm, and hence most likely to preserve characteristics of the earliest members of its clan (Nature, vol 402, p 404).

Found only on the south Pacific island of New Caledonia, Amborella is a relic fromthe earliest days of flowering plants. New Caledonia was once part of the southern supercontinent Gondwana but has been isolated for 55 million years. Consequently it is a Noah's ark of ancient plant species that have been outcompeted and driven to extinction elsewhere.

Further genetic studies found that the water lilies, a relative of theirs called Hydatella and a group of shrubs known as the Austrobaileyales (best known for the spice star anise) are almost as ancient as Amborella. These venerable living species could help fill in another blank: what did flowering plants evolve from? The ancestor must have been a gymnosperm, because they alone share with angiosperms the trait of being seed-bearing. But which one? Possible candidates include the extinct cycad-like Bennettitales and the palm-like Caytoniales.

Recent research on living plants has made inroads towards answering this question, though for now it remains unresolved. William Friedman of the University of Colorado, Boulder, has devoted the best part of a decade to studying primitive angiosperms. In 2002, he and colleague Joseph Williams discovered that the water lilies and Austrobaileyales have a unique embryo-nourishing tissue that looks distinctly gymnosperm-like. This led to suggestions that they form a living "missing link" between all other angiosperms and gymnosperms (Nature, vol 415, p 522).

More progress came earlier this year when Friedman discovered that Hydatella nourishes its seeds before fertilisation. In other words, it reproduces in the same wasteful fashion as gymnosperms, loading its seeds with food regardless of whether or not they will be fertilised (Nature, vol 453, p 94). "We are starting to break down some of the gap between angiosperms and gymnosperms," says Friedman.

Whatever angiosperms evolved from, DNA-sequence data suggests that it happened considerably earlier than even the pollen record shows. The very first flowering plants appeared perhaps as far back as 180 million years ago, in the early Jurassic, says a team led by Doug Soltis of the University of Florida in Gainsville (Annals of the New York Academy of Sciences, vol 1133, p 3).

These humble newcomers didn't make much of an impact, and it would be another 50 million years, late in the Jurassic, before the major angiosperm lineages made their debut. "There was a sudden burst of evolution between 144 and 140 million years ago that gave rise to all the major lineages of flowering plants," says Soltis. "We were astonished by how quickly they appear. That narrow window marks the beginning of their march to dominance," (Proceedings of the National Academy of Sciences, vol 104, p 19363).

"It is astonishing how quickly all the major lineages of flowering plant appeared"Ecological dominance truly arrived with the appearance of flowering "rosid" trees between 110 and 90 million years ago, says Pam Soltis of the Florida Museum of Natural History. "The fact that a number of rosid families radiate at the same time suggests a worldwide rise in angiosperm forests," she says. Most angiosperm trees are rosids, including oaks, beeches, baobabs and maples. With their emergence, flowering plants could dominate the entire forest ecosystem, from the understorey to the canopy, for the first time.

Let it bee

The emergence of the angiosperms had major evolutionary knock-ons, especially among insects, the foot soldiers of the floral revolution. In return for a small food reward, they evolved to carry pollen from flower to flower, allowing flowering plants to cut back on pollen production and conserve yet more valuable energy. Gymnosperms, in contrast, are mostly wind pollinated.

This mutual back-scratching has served the bees particularly well. They evolved from wasps early in the Cretaceous and have been inseparable from flowers ever since.

The rise of the bees spurred the evolution of ever larger and more elaborate blossoms as flowers competed for pollination services in a more competitive and crowded market. A study of fossil pollen from Minnesota, published this year, suggests that by 96 million years ago, some three-quarters of angiosperms were insect pollinated - a similar proportion to today. "Much showier flowers had evolved by then," says Dilcher, a lead author of the study (Proceedings of the National Academy of Sciences, vol 105, p 240). The world had burst into bloom.

Even the orchids, long regarded as recent in origin, turn out to have their roots in this late-Cretaceous blooming. Despite being one of the largest plant families, with some 22,000 species, their fossil record is barren. In 2007, however, a bee transformed our understanding of orchid origins. Some 15 to 20 million years ago, in what is now the Dominican Republic, this bee crawled into a flower and collected a patch of pollen on its back, only to be trapped in amber shortly afterwards. The pollen was almost identical to that of a living species of tropical American orchid, and researchers used this to calibrate a molecular clock. They concluded that the orchids appeared between 84 and 76 million years ago (Nature, vol 448, p 1042).

Around the same time came another major event in angiosperm evolution: the rise of the grasses, which do so much to shape the modern world. Domesticated grasses such as wheat, corn and rice feed us, while wild grasses dominate savannah and prairie landscapes. Grasses only became widespread 25 to 15 million years ago when cool, dry conditions kicked in. This harsher climate suited them well as most of the plant grows underground, enabling it to survive droughts and to regrow quickly after grazing or fire.

It turns out that grasses, too, have been around for longer than anyone thought. Fossilised dinosaur dung from 70 million years ago was recently found to contain silica particles of a type found only in grasses - firm evidence that grasses had diversified long before the dinosaurs went extinct 65 million years ago (Science, vol 310, p 1177).

Angiosperm diversity and abundance increased steadily through the Cretaceous and into the early Palaeogene period. By about 50 million years ago, the floral revolution was complete, with angiosperms dominant in almost all habitats. They had gone from being rank outsiders to global titans in the space of a few tens of millions of years.

Their influence didn't stop there. Our distant primate ancestors thrived in the ancient flowering forests, while early humans got their big break on the grassy savannahs of East Africa. More recently, human populations have exploded thanks to the cultivation of cereals, vegetables and fruit. Every step of the way, our own successes have depended on angiosperms. Flower power really does rule the world.