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‘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.

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.

Climbing vines

The vascular system of lianas has evolved to transport water hundreds of metres through the canopy.

Lianas take up water and nutrients for the plant from the forest floor, but in order for them to reach up to the top of the canopy they must be able to transport their nutrients through their elongated stems – as far as 900 metres in the most extreme examples. While the evolution of lianas has resulted in one of the most advanced water transport systems of any plant, there is a group of specialised plants that have found a way of living high up in the architecture of the forest trees without the need for long roots. These plants are known as epiphytes, or air plants, as they do not have roots which grow into the soil, but instead have short roots which can absorb nutrients and water from organic matter that accumulates on branches high up in the forest canopy. As these plants must absorb all of their water from the air, they can only thrive in very humid environments, and in the high-altitude montane forests of the tropics trees can become covered in epiphytic plants. Epiphytes include the mosses and lichens of temperate forests, but also a multitude of more complex plants such as orchids, ferns and some tropical cacti. However, there is one group of plants that stands out as the true masters of arboreal life, the tank bromeliads. Relatives of the pineapple, tank bromeliads live attached to the branches of trees in the rainforests of South America, where they display an amazing variety of shape and colour, from broad, green fleshy-leaved plants, to small, delicate purple and red structures. Their broad leaves are arranged into a basket-shaped rosette which acts to channel the rainwater that trickles through the forest canopy into a central reservoir, and the bases of these leaves are packed so tightly together that they are able to create a watertight tank in which the water can gather. In the largest species of tank bromeliad as much as 50 litres of water can be held between the plant’s leaves, and a study conducted in Puerto Rico found that in just a 1-hectare area of rainforest as much as 50,000 litres of water can be stored, which would fill a small swimming pool.

Tank bromeliads

These plants provide arborial homes for a whole host of animal life.

The little elevated lakes that gather in the bases of bromeliads make perfect homes for a handful of species looking to escape the perils of the forest floor. Insects such as mosquitoes lay their eggs in the pools of water, and flatworms find shelter among the leaves. With this abundance of insect life comes a menagerie of larger animals that visit the pools to munch on the invertebrate feast. Inch-long salamanders come to feast in the relative safety of the plant, and in some bromeliads in Jamaica small crabs have been found to dwell, territorially defending their plant against lizards and millipedes. Tiny poison dart frogs are perhaps some of the best-known lodgers, with some species spending their entire lives, from tadpole to adult, inside the seclusion of the bromeliad’s tank. A recent count of the different animals that live in the bromeliads of Ecuador found an astonishing 300 different animal species that made these plants their home. However, the bromeliad does not just provide a home for these animals to be of service, rather it accommodates them so they can provide it with food. The droppings of the frogs and salamanders, which contain the digested bodies of the insects that gather in the pool, accumulate in the water and can be absorbed by the plant as a vital source of nitrogen-rich food.

Back on the forest floor plants grow in a more conventional way, rooted to the ground. Although these plants only receive around 2 per cent of the glorious sunlight available at the top of the canopy, they have the advantage of growing directly on the nutritious layer of organic material created by an unseen army of bacteria and fungi. Species here are able to spread across the forest floor in a dense carpet of growth, employing a number of adaptations which allow them to thrive in the forest understorey. One such strategy is seen in the stripy-leafed Tradescantia zebrina from the forests of southern Mexico, which has purple undersides to its leaves created by a pigment called anthocyanin. As light passes through the green photosynthetic tops of the leaves the purple cells underneath act like a mirror and bounce the light back up to ensure that the maximum energy is absorbed by the plant’s chlorophyll. Other plants use size to their advantage to capture as much light as is physically available. One of the most successful plants at using this strategy is the giant taro plant, Alocasia robusta, which has the largest undivided surface area of any leaf on the planet, growing to over 3 metres in length and over 2 metres in width. Its huge glossy leaves thrive in the understorey of the tropical forests of Asia, where they fan outwards in order to gather light throughout as much of the day as possible. Another more subtle mechanism used by plants to ensure they can gather as much light as possible is found in a small purple-leafed shade-dwelling species called Oxalis oregana, from the redwood forests of western USA. At the top of its short 15 cm stems it has triplets of heart-shaped green leaves which are able to move in order to track the sparse sunlight as it shines through the canopy above. However, as Oxalis has adapted to photosynthesise in such low levels of light, strong sunlight can actually be damaging to its cells. Consequently, should a beam of sunlight break through the canopy directly onto its leaves, in just 6 seconds the plant can tilt its leaves to a vertical angle and escape the light.

Another group of prolific plants that thrive in forests are the palms, notable for their economic importance to us. Found growing both as tall trees with mighty crowns poking through the forest canopy and in short, spiky clumps at ground level, palms can live in habitats ranging from the desert islands of the hot tropics to the milder Mediterranean climes of the subtropics. They are instantly recognisable by their distinct leaves. Resembling thick, green feathers and broad, fan-like paddles, their leaves give them a surface for absorbing energy from the sun, and their deep ridges channel rainwater away from their surfaces. Various animals also rely on palms for food and shelter: birds such as palm-nut vultures and macaws flock to the plants to eat their fleshy fruits, and small, ground-dwelling mammals like the Asian palm civet (Paradoxurus hermaphroditus) forage for fruits about their bases. Madagascar has the highest diversity of palms anywhere on the planet, and because of the island’s lack of herbivores the leaves of its palms lack the chemical defences and spines found elsewhere. Some of the island’s palms have leaves that extend for no more than a few centimetres, but in the extreme example of the raffia palm (Raphia farinifera), its leaves can hang down from the crown a massive 24 metres – the longest known leaf of any plant, roughly the height of a seven-storey building. The largest seed of any known plant comes from a palm too, called the coco-de-mer or double coconut, and the largest known inflorescence comes from a species of palm called Corypha umbraculifera. The eighteenth-century Swedish naturalist and father of taxonomy, Carl Linnaeus, was so taken by palms that he labelled them as Principes, the order of the Princes.

Leaf architecture

Leaves are the food-making factories of green plants, and come in a variety of shapes and sizes.

Palms today provide humans with an array of useful materials and foods, and after grasses and legumes they are the most economically important plants on the planet. Nearly every part of the palm plant can be used for food: the sap is commonly boiled to create a sugary food called jaggery, and the oils from the flower are tapped to make a fresh drink or fermented and distilled to create a number of potent alcoholic beverages, such as the east Asian liquor arak. The sweet tips of the fresh leaf growth make a sweet salad, and the starch from the fibres of the trunk can be harvested to make a nutritious food called sago. As well as their multitude of edible uses, palms provide a variety of practical materials, both locally to where they are grown and across the world. Their wood is used to make buildings and furniture, as well as ropes, clothing and fibres, and the oil from their fruits can be turned into waxes, fuel and cheap cooking oil. Sadly, the oil produced from palms is in such high demand that great swathes of diverse tropical rainforest are being felled in Southeast Asia to be replaced with vast seas of oil-palm plantations.

Mighty bamboo

This member of the grass family is the strongest plant on the planet.

Less biologically rich than their tropical counterparts, the temperate forests are characterised by leafy deciduous vegetation and conifer-covered mountains. Unlike the tropics, which often have both wet and dry seasons, temperate regions have four distinct seasons of varying warmth and precipitation, and through this cycle some of nature’s most striking landscapes are created. In the mountain region of south-central China some of the most dramatic habitats of temperate vegetation can be found, nourished by the waters of the five great rivers of Asia: the Mekong, Irrawaddy, Yellow, Yangtze and Salween. These are the most biodiverse temperate habitats, and among the mountain woodlands giant pandas feed on one of the most important plants of these forests – bamboo. This mighty plant makes up a key part of the understorey of the temperate broadleaf deciduous forests.

Bamboo is a member of the grass family Poaceae. In fact, bamboo is the largest grass in the world. Separating it from all the other grasses is its tough, woody stem. This gives the strongest shoots the strength of mild steel (able to withstand around 52,000 pounds per square inch, a pressure that could crush stone), making it the strongest plant on Earth. Shooting upwards like an extending telescope, each new section of the plant extends from the centre of the old sections, and the fastest species are able to advance towards the light at a staggering rate of over 5 centimetres per hour. This amazing growing capability makes bamboo a crucial plant in its forest habitat, acting as an unrivalled soil erosion control agent. Bamboo is particularly successful at re-colonising areas of land that have previously been cleared for agriculture or cattle grazing, and the re-greening of an area of land by bamboo can help return structure and life to the forest environment.

Like palms, bamboo provides us with a vast variety of building materials and foods. Bamboo-related industries are estimated to provide a livelihood for around 1.5 billion people worldwide, making it a plant of great economic importance. In Asia it is used to create high rigs of scaffolding, some over 100 metres tall, and in Central America an area of farmed bamboo forest of just 60 hectares can provide enough material to build around a thousand small houses. But it is actually the less impressive relatives of the grass family that provide humans with an even greater service. These are the grasses that give us wheat, corn, rice and maize, and that feed the animals which give us meat, leather and wool. They are the most economically important plants on the planet, and their exploitation has shaped the face of the world as we know it.

Wild grasslands

Africa’s vast protected national parks provide a snapshot of how Earth’s ancient plains would have looked.

In their wild form grasses grow primarily in the semi-arid grasslands and savannahs that make up about 20 per cent of the Earth’s surface. In the past, thousands of grazing animals such as elk, wild horse and saiga antelope inhabited these vast grasslands. Today these wild habitats are much quieter. Hunters who roamed the grasslands some 20,000 years ago caused the mega-herbivores that once dominated the landscape to disappear. Today it is primarily livestock that inhabit these landscapes. Protected habitats such as Yellowstone National Park in the USA and the Masai Mara National Reserve in Kenya now form some of the few grassland areas where one can get a glimpse of how our grassland ecosystems would have looked without human interference.

Plants that grow in grasslands are highly resilient to drought, and are often able to withstand months without rainfall. Short hairy grasses such as june grass (Koeleria cristata), which grows in North America’s dry prairies, have shallow roots that sit just under the surface of the ground, so that as rainwater soaks into the ground it can be absorbed by the plant. Conversely, taller grasses like elephant grass (Pennisetum purpureum), which grows to around 5 metres and, as its name suggests, is a favoured food of Africa’s largest herbivore, have hair-like, branching roots reaching up to 6 metres in length, enabling them to reach sources of water held deeper in the soil. As a means of saving water, many grasses also have long, narrow leaves which lose far less water in the drying sun than larger leaves would.

Kingdom of Plants: A Journey Through Their Evolution

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