Academic Reading — Test 100

Reading passage

In the harsh gravel plains of the Namib Desert, which stretches along the south-western coast of Africa, grows one of the most extraordinary plants on Earth. Known to botanists as Welwitschia mirabilis, this low, sprawling organism appears at first glance to be little more than a heap of withered leaves. Yet appearances deceive. Many individual specimens are believed to be between 500 and 1,500 years old, and a small number may have survived for well over two millennia. Because the plant has changed very little over an immense span of geological time, scientists frequently describe it as a "living fossil", a survivor from an ancient lineage that has otherwise vanished. Its endurance in a landscape that receives almost no rain has made it a subject of fascination for researchers seeking to understand how life persists under extreme conditions. The Welwitschia produces only two leaves during its entire lifetime, and these continue to grow from their base year after year. Unlike most plants, it never sheds these leaves and grows replacements. Instead, the original pair is retained for centuries, gradually splitting and fraying at the tips as the desert wind and blowing sand tear them apart. This splitting creates the misleading impression of a tangled mass of foliage, but in reality the appearance is the product of just two ever-lengthening leaves. A leaf may eventually reach several metres in length before the worn edges crumble away. The plant grows from a short, woody, cup-shaped stem that rarely rises far above the ground, while a long taproot descends deep into the soil. This combination of a squat profile and a buried root system helps the plant withstand both fierce winds and the scorching heat that radiates from the desert surface. Survival in such an environment depends above all on the capture of scarce moisture. Although meaningful rainfall in parts of the Namib may occur only once in several years, the coastal region is regularly blanketed by thick fog that rolls inland from the cold Atlantic Ocean. For a long time, biologists assumed that the broad leaves of the Welwitschia absorbed this fog directly through tiny pores on their surface. More recent investigation has cast doubt on that explanation. The prevailing view now holds that fog condenses on the leaves, drips to the ground, and is then taken up by the plant's roots, which spread widely through the upper layers of the soil. In this way the plant exploits a water source that many other species cannot use, turning the very mist that shrouds the coast into a lifeline. The plant's biology is unusual in other respects too. Welwitschia is dioecious, meaning that individual plants are either male or female, and pollination is required for reproduction. The cones it produces are a vivid colour that attracts insects, and pollinating insects are drawn to a sugary fluid secreted by the cones. Once a seed has formed, however, its prospects are bleak: the vast majority of seeds never germinate, and those that do require an unusually wet season to establish themselves. Such favourable seasons are rare, which means that successful reproduction occurs only at long intervals. This explains why populations of the plant tend to consist of individuals of widely differing ages rather than dense stands of young seedlings. The extreme longevity of the Welwitschia is matched by an extremely slow pace of life. Its metabolism is geared towards conservation rather than rapid growth, and it can endure prolonged periods during which almost nothing happens. This patience is itself a survival strategy: by minimising the resources it expends, the plant can persist through droughts that would kill faster-growing competitors. Its tissues are also tough and resistant to the damage caused by intense ultraviolet radiation and by the grazing of desert animals, which find the bitter leaves largely unappealing. Few creatures attempt to eat the plant, and those that do rarely return for a second meal. Today the Welwitschia is regarded as a symbol of resilience, and it features on the national coat of arms of Namibia. Although it is not currently considered to be in immediate danger of extinction, conservationists monitor it closely. The slow rate at which it reproduces means that any sudden loss of mature plants would be difficult to reverse within a human lifetime. Threats such as off-road vehicles, which damage the fragile desert crust, and the collection of specimens by enthusiasts are watched with care. For now, however, this remarkable plant continues to do what it has always done: endure, quietly and almost unchanged, in one of the driest places on the planet.