Kernels of the future
Paul Smith celebrates the history of seeds, travellers in space and time of different shapes sizes and colours
Seeds are amazing. They can travel thousands of miles across oceans and continents, and can live for hundreds of years. A seed no bigger than a pinhead can grow into the tallest living organism on the planet. The smallest seed can barely be seen with the naked eye; the largest is the size of a human head. Over a period of more than 300 million years, seeds have evolved into every size, shape, and colour imaginable.
Seed-bearing plants
Botanists estimate that there are more than 370,000 seed-bearing plant species, found throughout the world. And with around 2,000 new species being discovered and described each year, that figure continues to grow.
Conversely, with vast tracts of primary vegetation being cleared for human use – particularly for agriculture – many plant species are disappearing without our knowledge.
Current estimates suggest that one in five of the world’s plant species are threatened with extinction.
However, as is the case with all biological diversity, there are too few scientists, horticulturalists, foresters, ecologists, and natural resource managers to document the status of the world’s plant diversity with sufficient accuracy.
This matters because plants are fundamental to the ecology of this planet and, by extension, to our survival. They convert energy from the sun and turn it into food, forage, building materials, medicines, and other products for our use, and, equally importantly, are key components of the ecosystem services essential to life on Earth, including the water, carbon, and nitrogen cycles.
Plant life on land evolved a staggering 600 million years ago, with the ancestors of many of these early plants still extant today: the mosses, clubmosses, horsetails, and ferns. These species don’t produce flowers or seeds; instead, they reproduce through spores. It was not until approximately 240 million years later that the first primitive seed-bearing plants appeared.
What is a seed?
Seeds are travellers in space and time – small packages of DNA, protein, and starch that can move over long distances and remain viable for hundreds of years. These packages have everything they need not only to survive, but also to grow into a plant when they encounter the right conditions.
Seed morphology
Seeds have developed a wide range of shapes and sizes in order to maximise their chances of survival, in particular through adaptation for the two most important stages of their development – dispersal and germination. Wind-dispersed seeds, for example, may be very small and light, or they may develop wings or other appendages that enable them to fly or float on air currents for long distances. Waterborne seeds, such as the coconut, have a thick, impermeable seed coat enabling them to float on water.
Animal – or bird–dispersed seeds have a variety of adaptations that enable them to hitch a ride with their dispersers. These include hooks or grapples on their seed coats that stick to fur; or tasty, often brightly coloured seed arils that are attached to the seed and picked up, carried away and eaten, leaving the fertile part of the seed to germinate; and a hard, resistant seed coat enclosed in a sweet, juicy fruit that enables the seed to pass through the gut of an animal or bird and emerge intact and ready to germinate.
Seed conservation
Humans have been storing seeds for millennia in order to grow them in their gardens or fields the following year. However, the science of seed conservation really only gathered momentum in the 20th century.
While the science of seed conservation was pioneered by the agricultural research community, botanic gardens like Kew started to develop their own seed banks and research from the 1960s onward.
In 2000, Kew opened the Millennium Seed Bank at its country site, Wakehurst Place in Sussex. At the time, this was the largest seed bank in the world, designed to store seeds from a wide array of plant species, not just crops.
Since then, other large seed banks with a focus on wild species have been established. In 2008, the Global Seed Vault opened in Svalbard in the Arctic Circle. This facility is unmanned, and is designed as a “back-up” store for all of the world’s crop varieties.
Most seed banks have multiple roles, including seed collection, seed storage, and seed supply, and they carry out research associated with all of these activities. n
Plants are fundamental to the ecology of this planet and, by extension, to our survival
The Book of Seeds: A Lifesize Guide to 600 Species from Around the World by Paul Smith, is published by Ivy Press in February 2018 at £30.