around a tall speckled-green and cream-coloured flower-bearing spike, which is made of separate male and female flowers.
Only staying open for a couple of days, the titan arum has to attract as many of its pollinators as quickly as it can, and it does this by emitting a foul and fetid stench, described as resembling rotting flesh, sour dairy and burnt sugar, which is produced by sulphur-containing compounds on its spike. The stench of the recently opened flower is in fact so vile that the artist who came to draw the first specimen that came into flower at Kew was made ill after inhaling it for too long. Shortly after opening, the base of the flowering spike begins to generate heat of around 36°C, which creates a convection current to help waft its rancid smell through the night air. By burning reserves of stored carbohydrates, the plant produces heat in waves over a few hours, and the resulting pulse of scent that is emitted acts to punch through the layer of cooler air that forms below the forest canopy. Once through this layer, the foul scent is able to travel great distances through the forest and reach the olfactory organs of its pollinators. Any carrion-beetles or flesh-flies that catch a whiff of its odour will then hungrily fly to the flower expecting to find a meal of decaying meat, and on arrival will bump into the flower spike. Cunningly, the male and female parts of the titan arum open on separate nights to prevent the flower from self-pollinating, so it has female parts at the bottom which open on the first night, and male parts on the top which open later. As flies search the flower for the source of the rancid smell they become caught in the deep cone of the flower’s collar, and in order to escape they must crawl up the flower spike, getting coated in pollen as they go. They then fly to another open flower and, starting at the bottom again, crawl upwards – and in doing so cross-pollinate the flowers. Since the 1800s titan arum has flowered numerous times at botanical gardens across the globe where it is now showcased, perhaps most notably at Kew in 1926, when police were called in to control the huge crowds that had gathered to see and smell the much-talked-about spectacle. Titan arum plants are now grown by botanical institutions and private collectors all around the world, but the occasions when their blooms emerge still make the headlines.
Door-to-door transfer
Flowers provide an elegant door-to-door pollen delivery system for plants.
© Minden Pictures/SuperStock
The dizzying diversity of flowering plants today is truly staggering, and we continue to discover further members of these incredible plants, such as orchids which only flower under the cover of darkness and palm trees which flower themselves to death, flowers which imitate an incredible array of insects, and even flowers which mimic other flowers. In their long history, spanning over 400 million years, plants have developed many amazing strategies to better survive and reproduce, and the evolution of the flower is surely one of their greatest. Not only has it allowed angiosperms to outnumber their fern and conifer ancestors by 20 to 1, it has also helped forge the relationship between humans and plants. Many of the plants that today support the human population, such as the grasses that provide cereals and sugar, the many fruits and vegetables we eat, as well as cotton, coffee and chocolate, and trees that provide building materials, are the result of the evolutionary success of these flowering plants.
© Will Benson
‘Throughout history humans have looked for patterns in nature.’
Long before humans built the first houses out of mud, straw, wood and vines, plants employed organic material to create a multitude of structures, each one more advanced than the last. Plants use the powers of speed and size to push out the competition and overwhelm their adversaries. On the exposed slopes of wind-lashed mountainsides, plants use the powers of endurance and timing to survive the bitter winters. And in the bleakest deserts, plants use extreme structures to protect their bodies and employ chemical tactics to protect them from enemies.
The species that we can see in the world around us today bear the scars of their evolutionary history. They are the ones who passed on their genes more successfully. Every thorn on their stems, every ridge on their leaves and every berry on their branches is the accumulated result of millions of years of evolution. For every extreme of shape and structure that appears in the plant world, there is a story of adaptation and survival, to a particular climate or lifestyle that can explain them.
Every major habitat on Earth provides conditions favourable to a particular set of plants, which is why you will never find a drought-tolerant saguaro cactus growing in the middle of a moist rainforest, and you will never find a tropical mahogany tree setting down its roots in a desert. Their 450-million-year evolutionary journey has given each species of terrestrial plant a unique set of tools for survival in its specific environment, be it in the forests, the grasslands or the deserts. In each different habitat the temperature, the amount of water, the availability of light and the terrain itself determine which groups of plants can thrive there. In turn the plants and animals which already live in a habitat can limit or facilitate the addition of other species. In this way, complex ecosystems are built around an intricate network of plant, animal and fungal life, where each species is reliant on those species below it in the food chain, and in turn gives life to those above it.
Forested habitats provide an environment most similar to those in which plant life first emerged during the Devonian explosion, and it is in these habitats that we see the greatest diversity of life today. Rainforests alone contain more than 50 per cent of the world’s plant and animal species, and collectively, tropical rainforests, boreal forests and temperate forests make up 30 per cent of the Earth’s landmass. This makes them the most important habitat type in terms of the carbon-capturing and oxygenating services that they provide our biosphere with. Historically forests have been a lifeline, harbouring the survivors of the ice age that hit Earth at the end of the Cambrian. Plants in this habitat managed to survive, while those elsewhere perished in the cold, dry climate. These forests now make up the oldest continuously growing habitats on Earth, at around 135 million years old. In comparison, the tropical expanse of the Amazon is a relative infant at only 40 million years old. The ancient forests that sheltered the DNA of plant life on this planet can still be visited today, in places like the Daintree Rainforest on the northeastern coast of Queensland in Australia.
Ancient refugia
Australia’s Daintree Rainforest is the oldest continually growing habitat on Earth.
© imagebroker.net/SuperStock
In modern-day forests trees dominate the landscape, and their layers of leaves and branches create niches where many other forms of life can grow. The tallest trees benefit from broad canopies which can stretch above all other plants to absorb the most light, while plants living below have to adapt to make best use of the limited light that filters through to the lower layers. However, the trees at the top of the canopy must also endure the hottest temperatures and lowest humidity. Some of the largest forest trees are the largest plants on the planet: for example the giant sequoia, Sequoiadendron giganteum, which grows in the evergreen forests of central California. The largest can reach over 80 metres high, and contain enough wood to build over 40 small houses. One tree can support as many as a hundred other species of plant and animal. Woody vines called lianas use the tall trunks of trees to creep up towards the light at the top of the canopy. As they rely completely on the support of other vegetation they invest little energy in structural support, and as a result they put all of their resources into rapid growth and leaf production. There are over 2500 species of lianas which grow in the tropical forests of Africa, Asia and the Americas. As they grow, these tiny vines may remain thin and cling to the sides of trees, or may ultimately become colossally thick stems which appear as tough as tree trunks themselves. In some forests lianas have been found to make up over 40 per cent of the total leaves in the canopy.