Thorn-apple, Datura stramonium: This weed is not persistent
I have sent a leaf and cone of a plant growing in my garden this year. It has a lot of these cones and big leaves. I have no idea what it is, can you help? (Mrs B Prielis, Toftwood)
The plant you have sent in is known as a Thorn-apple, Datura stramonium. This is an introduced annual weed of cultivated fields, gardens and waste places with a large prickly fruit that gives the plant its name. It is a non-persistent weed that will have grown from seed that has come from several sources, including birdseed and wool and soybean waste.
Thorn-apple occurs sporadically throughout the UK particularly in hot summers.
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The large trumpet-like flowers are usually white but may have purple flowers.
The plant is poisonous to humans, horses, cattle, sheep, pigs, mules and chickens. Livestock normally avoid it but may be poisoned by eating contaminated hay, silage or seed screenings.
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Thorn-apple flowers from July to October. Seeds mature 30 days after pollination the seed capsule opens around 20 days after that. You may see up to 50 capsules per plant with 600-700 seeds in each capsule, this equates to 30,000 seeds per plant. Even when the plants have been cut down the seed will continue to ripen in the capsules.
Seeds taken from a partly green capsule that turn black on drying are fully viable. Immature seeds are said to germinate more readily than fully mature seed. Very ripe seed may germinate immediately after shedding but the majority soon becomes dormant.
The low germination rates are put down to many factors including an impermeable seedcoat. Cracking or chipping the seed coat allows germination to take place. Burial of seed increases the light requirement for germination to occur.
Sensitivity to light and the effect of gaseous diffusion in the soil around the seed allow it to perceive the proximity of the soil surface. Cultivation triggers seedling emergence; reburial of seed before germination reimposes dormancy.
In the field, seedling emergence occurred from May to August with peak emergence in May. After emergence, seedlings establish and grow rapidly to shade out surrounding vegetation.
The best method of control is to hand-pull small patches before seed is set. Seedlings are readily killed by cultivation and hoeing the area. Older plants may regenerate from cut down stumps. Without adequate control the weed will have built up to a high level in five to six years.
•This article was first published on October 15, 2011.