the mystery of how flowering plants evolved
By zteve t evans
An abominable mystery!
One of the great mysteries of the botanical world is how flowering plants managed to evolve and disperse across the globe so quickly. Writing in 1879, Charles Darwin called it an "abominable mystery" but now modern genetics could provide an answer to the puzzle. Twenty years after he wrote the groundbreaking, "The Origin of Species" setting out his ideas on biological evolution there still remains problems that he could not find an answer to. The mystery of how flowers evolved and spread around the world in such a relatively short span of time concerned him because it challenged his theory of gradual evolution through natural selection. Slowly modern studies are beginning to put the pieces of the jigsaw in place beginning to reveal the story of how flowering plants evolved.
One of the great mysteries of the botanical world is how flowering plants managed to evolve and disperse across the globe so quickly. Writing in 1879, Charles Darwin called it an "abominable mystery" but now modern genetics could provide an answer to the puzzle. Twenty years after he wrote the groundbreaking, "The Origin of Species" setting out his ideas on biological evolution there still remains problems that he could not find an answer to. The mystery of how flowers evolved and spread around the world in such a relatively short span of time concerned him because it challenged his theory of gradual evolution through natural selection. Slowly modern studies are beginning to put the pieces of the jigsaw in place beginning to reveal the story of how flowering plants evolved.
Darwin’s dilemma
All flowering plants belong to a group called angiosperms. This is a large and diverse group with plants such as lilies, cereals, grasses and gardenias for example as well shrubs, grasses, herbaceous plants and many trees. They differ from most other plants because they produce a flower which usually contains their seeds in some form.
The problem for Darwin was that the earliest examples found in the fossil record dated back to about 100 million years ago to around the middle of the Cretaceous period and were found in an incredibly wide range of shapes and sizes. This seemed to imply that flowering plants went through a sudden burst of evolutionary development relatively soon after their origin, which did not match with Darwin's theories. However, recent research indicates that angiosperms did in fact evolve slowly over time, but this still leaves important questions that need answering.
Questions of evolution
There are about 350,000 known flowering plants which is about 90% of all known living species of plants. They play a huge part in the global ecosystem and are vital to humans. All the main crops, including animal feed, that humans rely on are angiosperms. They are also important carbon sinks soaking up significant amounts of carbon dioxide from the air. Without them life on Earth would be very different. The questions scientists want answering are how and where they originated, how did they achyieve such diversity and how did they become so tremendously successful?
Darwin's theories helped establish a framework to explain the evolution of new species and he believed it happened slowly and gradually over a long period of time. In the Origin of Species he wrote, "As natural selection acts solely by accumulating slight, successive, favourable variations, it can produce no great or sudden modification; it can act only by very short and slow steps."
Nevertheless, he was aware that there could have been exceptions to such a rule and the origins and evolution of flowering plants could possibly be one of them. Angiosperms were a mystery because they had not existed in the greater part of the history of the Earth, suddenly seeming to appear on the scene in the Cretaceous Period.
The appearance of angiosperms
Primeval forests were populated by strange plants that were relatives of horsetails and club mosses which today play minor roles in plant communities. Succeeding these came the gymnosperms which were a group of plants that produced unenclosed seeds, such as conifer trees produce cones, became dominant. Angiosperms appeared after these.
All flowering plants belong to a group called angiosperms. This is a large and diverse group with plants such as lilies, cereals, grasses and gardenias for example as well shrubs, grasses, herbaceous plants and many trees. They differ from most other plants because they produce a flower which usually contains their seeds in some form.
The problem for Darwin was that the earliest examples found in the fossil record dated back to about 100 million years ago to around the middle of the Cretaceous period and were found in an incredibly wide range of shapes and sizes. This seemed to imply that flowering plants went through a sudden burst of evolutionary development relatively soon after their origin, which did not match with Darwin's theories. However, recent research indicates that angiosperms did in fact evolve slowly over time, but this still leaves important questions that need answering.
Questions of evolution
There are about 350,000 known flowering plants which is about 90% of all known living species of plants. They play a huge part in the global ecosystem and are vital to humans. All the main crops, including animal feed, that humans rely on are angiosperms. They are also important carbon sinks soaking up significant amounts of carbon dioxide from the air. Without them life on Earth would be very different. The questions scientists want answering are how and where they originated, how did they achyieve such diversity and how did they become so tremendously successful?
Darwin's theories helped establish a framework to explain the evolution of new species and he believed it happened slowly and gradually over a long period of time. In the Origin of Species he wrote, "As natural selection acts solely by accumulating slight, successive, favourable variations, it can produce no great or sudden modification; it can act only by very short and slow steps."
Nevertheless, he was aware that there could have been exceptions to such a rule and the origins and evolution of flowering plants could possibly be one of them. Angiosperms were a mystery because they had not existed in the greater part of the history of the Earth, suddenly seeming to appear on the scene in the Cretaceous Period.
The appearance of angiosperms
Primeval forests were populated by strange plants that were relatives of horsetails and club mosses which today play minor roles in plant communities. Succeeding these came the gymnosperms which were a group of plants that produced unenclosed seeds, such as conifer trees produce cones, became dominant. Angiosperms appeared after these.
Adolphe Theodore Brongniart a 19th century scientist began the task of collating all known information on plants. From his work it was shown that a great variety of angiosperms, also known as dicotyledons, or higher plants, suddenly appeared around the middle of the Cretaceous period.
This sudden appearance of flowering plants as well as being puzzling seemed to challenge Darwin's evolutionary theories of gradual evolution. Writing to Oswald Heer, the Swiss naturalist, in 1875 he said, "The sudden appearance of so many Dicotyledons… appears to me a most perplexing phenomenon to all who believe in any form of evolution, especially to those who believe in extremely gradual evolution."
In Darwin's time not all scientists agreed with his theories of gradual evolution. One thing that could be depended upon was that for every scientist with a theory there was another with a counter theory or determined to prove it wrong. The sudden appearance of angiosperms was used by his critics against him and his theories.
As a crude counter to his critics Darwin proposed that angiosperms could have evolved gradually over along period of time in a remote part of the world that had yet to be explored by scientists. Then during the middle of the Cretaceous period something happened that caused or enabled them to spread from their original home to the rest of the world. But Darwin knew that this could present the misleading idea that a variety of different flowering species suddenly evolved and was aware that his lack of supporting evidence left the theory weak.
Modern studies
Modern genetic studies and new finds of fossilized specimens show Darwin was close but not quite right. Specimens of angiosperms that are tens of millions of early than the middle of the Cretaceous period have been found in China but to complicate matters earlier specimens have also been found in the United States of America and also Europe.
Although knowledge has increased since Darwin's time there is still little expert consensus to when and where angiosperms first appeared. Nevertheless, because they appear in the fossil record much earlier this is seen as supporting Darwin's gradual evolution theory. Even so, there are still ongoing questions about how they spread and achieved such amazing diversity. Laurent Augusto at the National Institute for Agricultural Research in Bordeaux, France says, "Our world is an angiosperm world," says Augusto. "In many ecosystems they dominate in species and in biomass – this angiosperm ecological dominance remains unexplained."
This sudden appearance of flowering plants as well as being puzzling seemed to challenge Darwin's evolutionary theories of gradual evolution. Writing to Oswald Heer, the Swiss naturalist, in 1875 he said, "The sudden appearance of so many Dicotyledons… appears to me a most perplexing phenomenon to all who believe in any form of evolution, especially to those who believe in extremely gradual evolution."
In Darwin's time not all scientists agreed with his theories of gradual evolution. One thing that could be depended upon was that for every scientist with a theory there was another with a counter theory or determined to prove it wrong. The sudden appearance of angiosperms was used by his critics against him and his theories.
As a crude counter to his critics Darwin proposed that angiosperms could have evolved gradually over along period of time in a remote part of the world that had yet to be explored by scientists. Then during the middle of the Cretaceous period something happened that caused or enabled them to spread from their original home to the rest of the world. But Darwin knew that this could present the misleading idea that a variety of different flowering species suddenly evolved and was aware that his lack of supporting evidence left the theory weak.
Modern studies
Modern genetic studies and new finds of fossilized specimens show Darwin was close but not quite right. Specimens of angiosperms that are tens of millions of early than the middle of the Cretaceous period have been found in China but to complicate matters earlier specimens have also been found in the United States of America and also Europe.
Although knowledge has increased since Darwin's time there is still little expert consensus to when and where angiosperms first appeared. Nevertheless, because they appear in the fossil record much earlier this is seen as supporting Darwin's gradual evolution theory. Even so, there are still ongoing questions about how they spread and achieved such amazing diversity. Laurent Augusto at the National Institute for Agricultural Research in Bordeaux, France says, "Our world is an angiosperm world," says Augusto. "In many ecosystems they dominate in species and in biomass – this angiosperm ecological dominance remains unexplained."
The discovery of Amborella
The discovery of of a plant named Amborella on the small island of New Caledonia situated some 1,600 km east of Australia has shed some light on the origins of angiosperms botanists believe. The plant was discovered around the time Darwin was wrestling with the origins of flowering plants and how they fit, or do not fit, into his theory of gradual evolution.
Although the plant looks rather unimpressive studies by botanists over the last 100 years reveal that it is the only known survivor from one of the earliest branches of angiosperms. Scientists believe they can learn a great deal of the origins of flowering plants from Amborella as it is a living relic of the first flowering plants.
From the Amborella Genome Project a preliminary outline of the plant's genome has been uncovered that indicates the first angiosperms evolved from a species of gymnosperm at a time in history when the gymnosperms were the dominant world species. This leads scientists to believe that the first angiosperms evolved about 200 million years ago from 'whole genome doubling' in the ancestral gymnosperm. From their earliest history flowers are believed to have been the defining feature of angiosperms.
The discovery of of a plant named Amborella on the small island of New Caledonia situated some 1,600 km east of Australia has shed some light on the origins of angiosperms botanists believe. The plant was discovered around the time Darwin was wrestling with the origins of flowering plants and how they fit, or do not fit, into his theory of gradual evolution.
Although the plant looks rather unimpressive studies by botanists over the last 100 years reveal that it is the only known survivor from one of the earliest branches of angiosperms. Scientists believe they can learn a great deal of the origins of flowering plants from Amborella as it is a living relic of the first flowering plants.
From the Amborella Genome Project a preliminary outline of the plant's genome has been uncovered that indicates the first angiosperms evolved from a species of gymnosperm at a time in history when the gymnosperms were the dominant world species. This leads scientists to believe that the first angiosperms evolved about 200 million years ago from 'whole genome doubling' in the ancestral gymnosperm. From their earliest history flowers are believed to have been the defining feature of angiosperms.
How did angiosperms achieve such diversity?
Darwin was open to the possibility that it was the flowers that were the cause of such diversity, despite still being puzzled over the seemingly sudden appearance of angiosperms in the plant kingdom. In a letter to Darwin the French biologist, Gaston de Saporta suggested that the problem of the 19th century fossil record not showing the appearance of angiosperms need not be a problem for Darwin's ideas on gradual evolution, or their seemingly sudden appearance. He suggested instead that angiosperms were an exception to the general rule and their appearance was an unusual event. Saporta further suggested that the insects that pollinated flowering plants evolved alongside the flowering plants causing both to diversify with unusual speed.
Although Darwin accepted this explanation we know today that the first flowers were very plain and it is thought they may have not been that attractive to pollinators though their scent, if they had one, may have been. Scientists think that angiosperms had diversified greatly by the time the big, brightly colourful flowers evolved that attracted pollinators
In 2009, Frank Berendse and Marten Scheffer of Wageningen University, Netherlands advanced the theory that angiosperms were more productive than gymnosperms such as conifers and outcompeted them by being able to take a major share of the nutrients.
Earlier in the same year a team from the University of Tasmania in Hobart, Australia led Tim J Brodribb and been involved in study that looked at fossilized leaves to learn more about the rise of angiosperms. They concluded that angiosperms gained more veins during the Cretaceous period which would have given them extra water available to contribute to the process of photosynthesis giving them ability to grow faster. Nevertheless this is still not conclusive. Even though the leaves of angiosperms were better at photosynthesising than the small needles of conifers it may be that the total surface area of the needles of conifers provide a wider surface area than many angiosperms. "Very probably no single theory can explain the massive rise of the angiosperms," acknowledges Berendse.
Augusto thinks it likely that more than one factor was involved in the the rise of flowering plants. He thinks Berendse and Scheffer’s theory may work in the tropical regions where nutrient rich soil would help angiosperms out compete gymnosperms but it may not stand up in regions which have insufficient nutrients in the soil to give flowering plants the edge. It may also be that the plain and basic flowers of the first angiosperms made little or no difference to their initial evolution but over time as they gradually evolved more complex and colorful flowers it provided them with the stimulus to dominate.
A more detailed picture
Knowledge of how flowering plants evolved and spread has moved on considerably since Darwin's time thanks to modern techniques and new fossilized finds. There are still questions to answer about how flowering plants achieved such great diversity and how they have managed to dominate the plant world, but hopefully as science progresses and new techniques are utilized and more fossils are found a fuller, more detailed picture, may emerge telling the story of the evolution of flowering plants..
© 08/01/2015 zteve t evans
Darwin was open to the possibility that it was the flowers that were the cause of such diversity, despite still being puzzled over the seemingly sudden appearance of angiosperms in the plant kingdom. In a letter to Darwin the French biologist, Gaston de Saporta suggested that the problem of the 19th century fossil record not showing the appearance of angiosperms need not be a problem for Darwin's ideas on gradual evolution, or their seemingly sudden appearance. He suggested instead that angiosperms were an exception to the general rule and their appearance was an unusual event. Saporta further suggested that the insects that pollinated flowering plants evolved alongside the flowering plants causing both to diversify with unusual speed.
Although Darwin accepted this explanation we know today that the first flowers were very plain and it is thought they may have not been that attractive to pollinators though their scent, if they had one, may have been. Scientists think that angiosperms had diversified greatly by the time the big, brightly colourful flowers evolved that attracted pollinators
In 2009, Frank Berendse and Marten Scheffer of Wageningen University, Netherlands advanced the theory that angiosperms were more productive than gymnosperms such as conifers and outcompeted them by being able to take a major share of the nutrients.
Earlier in the same year a team from the University of Tasmania in Hobart, Australia led Tim J Brodribb and been involved in study that looked at fossilized leaves to learn more about the rise of angiosperms. They concluded that angiosperms gained more veins during the Cretaceous period which would have given them extra water available to contribute to the process of photosynthesis giving them ability to grow faster. Nevertheless this is still not conclusive. Even though the leaves of angiosperms were better at photosynthesising than the small needles of conifers it may be that the total surface area of the needles of conifers provide a wider surface area than many angiosperms. "Very probably no single theory can explain the massive rise of the angiosperms," acknowledges Berendse.
Augusto thinks it likely that more than one factor was involved in the the rise of flowering plants. He thinks Berendse and Scheffer’s theory may work in the tropical regions where nutrient rich soil would help angiosperms out compete gymnosperms but it may not stand up in regions which have insufficient nutrients in the soil to give flowering plants the edge. It may also be that the plain and basic flowers of the first angiosperms made little or no difference to their initial evolution but over time as they gradually evolved more complex and colorful flowers it provided them with the stimulus to dominate.
A more detailed picture
Knowledge of how flowering plants evolved and spread has moved on considerably since Darwin's time thanks to modern techniques and new fossilized finds. There are still questions to answer about how flowering plants achieved such great diversity and how they have managed to dominate the plant world, but hopefully as science progresses and new techniques are utilized and more fossils are found a fuller, more detailed picture, may emerge telling the story of the evolution of flowering plants..
© 08/01/2015 zteve t evans
References and Attributions
Copyright 8th January 2015t zteve t evans
Copyright 8th January 2015t zteve t evans