Cornfield Flowers: Arable Weeds

Arable weeds such as poppies produce millions of seeds per acre. These seeds sometimes lie dormant for many years before growing into the familiar blaze of vivid colour.

Arable weeds must tolerate ploughing, harvesting, chemical weedkillers and so on, as well as changes in the use to which particular fields are put from year to year. Weeds thrive in the spaces between rows of corn, in many cases benefiting from the crop fertilisers.

Field weeds are usually annuals, living for only one season and shedding large numbers of seeds before they die. Some, such as spurges, produce many generations in a single summer. Others are perennials.

Poppies are annuals and their scarlet blooms are an attractive sight throughout the countryside in summer. Surprisingly, there are no truly native poppies in the British Isles today, for they are always found on disturbed land. Where the poppy lived before farms and fields existed remains a mystery, and since archaeologists have found poppy seeds mixed with ancient Egyptian barley grains that are 3500 years old, poppies have obviously been weeds found growing with crops for a very long time.

In their association with man, poppies have been used in several ways. Syrup was extracted from the petals, and oils in the seeds were used for cooking and in paints. The pale lilac opium poppy has been grown in gardens since the Bronze Age for its morphine content, and related chemicals occur in some of our more common species.

There are eight species of poppy in the British Isles and five are still found as arable weeds. The field poppy is the most abundant: its wiry stems bear bright scarlet cup-shaped flowers with a dark blotch at the base. The flowers have no nectar but their copious, protein-rich pollen is collected by honey bees as food for the young larvae. The three most common species (right) are easily distinguished by their seed capsules which appear in late summer.

Many other arable weed species are found in their natural habitats, giving us a clue to their origins before agricultural activity was widespread. Scentless mayweed, for example, grows on coastal shingle and cliffs where it tends to have thicker, fleshier leaves than its cornfield counterpart.

Germination of weed seeds characteristically does not happen all at once. Some seeds germinate within a few weeks of being shed, and others do so later in the season. Many weed seeds are deeply buried and can remain buried alive for hundreds of years until the land is disturbed.

This is why enormous numbers of poppies covered the fields of Flanders after the battles of World War I. The massive disturbance caused by shell holes and trenches provided ideal conditions for the germination of millions of poppy seeds, a spectacular phenomenon still recalled more than 70 years later when we wear poppies in our buttonholes on Remembrance Day.

Perennial weeds have different strategies for coping with field life. Although the broad-leaved dock and the dandelion, for example, may produce enormous numbers of seeds, they also rely on their roots to produce new plants. They have fleshy roots which, when chopped up by ploughing, produce a new plant from each fragment.

Since weeds invaded the cornfields, many species have adapted to a specialised existence. Scentless mayweed, for example, growing in cornfields has developed a short life cycle similar to the crops among which it grows, whereas its cliff-dwelling relations are usually perennial plants. Other weeds grow fast, to the same height and maturing at the same time as crops. Many are resistent to weedkillers, producing rapidly germinating seeds that are often wind dispersed.

28. July 2011 by admin
Categories: Wildflowers | Tags: , | Comments Off on Cornfield Flowers: Arable Weeds

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