Dr Paul Smith is head of Kew's Millennium Seed Bank. Here he expresses his opinion on the threats to plant diversity and the importance of protecting it.
Kew, England (CNN) -- The extinction of species like the dodo, elephant bird, Tasmanian tiger and pink pigeon have made little impact, but more charismatic species, such as the panda, gorilla and tiger currently stand on the brink.
If we lose any of these species through our own carelessness, we will undoubtedly mourn their passing. However, the impact on humanity will be small. With plants, the opposite is true.
To the majority of people, plants are not charismatic -- they aren't warm and cuddly, and they don't have big eyes that ask questions. And yet these countless, nondescript plants have important roles in maintaining life on this planet.
They sit at the base of the trophic pyramid, providing food all the way up the chain to us right at the top. They provide services such as climate regulation and flood defense. They contribute to soil formation and nutrient cycling, and they provide us with shelter, medicines and fuel.
Despite this, the Millennium Ecosystem Assessment estimates that between 60,000 and 100,000 plant species are threatened with extinction -- this is between one quarter and one third of the total number of known plant species.
The main threats are land use change and over-exploitation with climate change expected to exacerbate the situation.
Why should we care? There are a number of reasons.
The first reason is that these plants may well be useful to us in unknown ways. The American naturalist, Aldo Leopold, wrote more than 70 years ago:
"If the biota, in the course of aeons, has built something we like but do not understand, then who but a fool would discard seemingly useless parts? To keep every cog and wheel is the first precaution of intelligent tinkering."
Since Leopold penned those words, the scientific discipline of ecology has demonstrated time and again that all productive systems are built on a web of interrelatedness.
This is manifest in the simple relationships between plants, pollinators, pests and predators in our agricultural systems but is true of all ecosystems, including the planet as a whole.
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We humans are not exempt from this. We are at the center of this planet's ecology, and are becoming more and more dominant. A seemingly irrelevant plant may be essential to the life cycle of a pollinator.
It may be the symbiont of a useful fungus or it may be home to an insect or bird that keeps a crop pest in check. We condemn plants to extinction at our peril.
A second reason that we should care is because ecology has also taught us that resilience is found in diversity.
The farmer who plants just one crop is far more susceptible to the vagaries of climate or disease than the farmer who plants a range of crops with a range of requirements and susceptibilities. The problem is that as a species we have forgotten this.
Increasingly, we rely on simpler systems and a rapidly dwindling range of plant diversity. Eighty percent of our calorie intake comes from just twelve plant species -- eight grains and four tubers. This despite the fact that at least 30,000 species of plants are edible.
Foresters primarily use around 100 tree species throughout the world despite the fact that there are 60,000 species of tree we could be using. In western medicine, we have only screened 20 percent of the world's plant species for pharmaceutical activity even though 75 percent of the world's population relies on wild plants for their primary health care.
As the world grapples with the big environmental challenges of our day -- food security, water availability, less land, climate change, deforestation, overpopulation, energy -- we have to ask ourselves, "Can we continue to rely on such a tiny fraction of the world's plant diversity for all of our future needs?"
Logic suggests that we can't. We will need new food crops that use less water or that are resilient to climate change. We will need to reforest catchment areas with more complex mixtures of trees that are not susceptible to pests and diseases. And we will need to develop first generation biofuels that do not displace food crops.
Finally, we should be saving plant species from extinction because we can.
With the range of techniques available to us, there is no technological reason why any plant species should become extinct. Where possible, we should be protecting and managing plant populations in the wild. Where we can't do this, we should be keeping them in seed banks and in gardens.
It is our responsibility - the responsibility of this generation -- to give our children every opportunity, and that means safeguarding, and passing on our biological inheritance intact. The Millennium Seed Bank Partnership epitomizes this philosophy in action.
We will be judged not just by what we build, but by what we leave behind.