Pineapple weed seeds uk

Pineapple Weed, Matricaria discoidea

Plants make an impression in different ways. I love Erigeron karvinskianus (Mexican Fleabane) for its prolific flowers, Gunnera manicata for its giant leaves and Calabrese for its taste.

It is the smell of Pineapple Weed, Matricaria discoidea, that I like. It is usually my first impression of the plant, as I accidentally step on it as I walk along footpaths, pavements or over waste ground. It is a scent that takes me back to childhood and warm summer days in the countryside.

I first knew Pineapple Weed by its older scientific name of Matricaria matricarioides. It also has other English names, including ‘wild chamomile‘, ‘disc mayweed‘, ‘pineapple mayweed‘ and ‘apple virgin‘. It is a member of the daisy family, the Asteraceae, and has a rich smell of pineapple when crushed.

Its close relatives Chamomile and the Mayweeds* (which have a similar smell) have more typical ‘daisy’ flowers, with white ray florets around the outside of the flower head and tube florets in the centre. Pineapple Weed just has the tube florets, which are like small yellow buttons. It is either the plant’s smell or the shape of its flowers that give it the name Pineapple Weed.

Pineapple weed is an annual herb which flowers from June to September in the UK. It is not native to Europe, however, and was introduced to Britain in 1781 from North America. It escaped from Kew Gardens in 1871 and soon spread. In Finland it was first grown in Kaisaniemi Botanic Garden in Helsinki in 1849 but within a year it had escaped and is now found throughout the country.

Pineapple Weed is a native of North-east Asia and the North-west United States. It is usually found growing in poor, compacted soils and roadsides. My nearest patch is on the verge of George Borrow Road in Norwich; I took the photograph above when walking from Bamburgh to Seahouses in Northumberland in June this year.

Pineapple Weed is edible, though some people are allergic to it. The chemical that gives the plant its characteristic fruity smell is a terpene called myrcene, which is also found in Basil, Hops, Mangoes and Cannabis. The plant also contains a coumarin called herniarin, and this may be responsible for the allergic reaction. The chemical has a range of biological activities, including haemostatic and anthelmintic properties (i.e. it can stop bleeding and can be used to expel parasitic worms). Extracts of Pineapple Weed also have antimicrobial properties.

Pineapple Weed’s ribbed seeds can be spread on footwear. However, in “The Roadside Wildlife Book” (1974) and “Flora Britannica” (1996), Richard Mabey suggests that the motor car, and pneumatic tyres in particular, aided the spread of the plant in Britain, as the seeds stick to tyres. He quotes an experiment: in 1968 a car had its tyres carefully washed and was then driven along 65 miles of road following heavy rain, including passing places and field gateways. The tyres were then hosed down and the sediment was incubated in sterilised compost. Plants from 13 different species grew, including 220 seedlings of Pineapple Weed.

Pineappleweed

An introduced annual weed of wasteland and bare places by paths. Pineappleweed was introduced into the UK just prior to 1900 and within 25 years it had spread along roadsides throughout most of England. Pineappleweed is now common throughout the UK, and is still increasing, especially on tracks and paths and on cultivated land. It prefers an open loamy or sandy loam soil.

Pineappleweed occurs in cereals and broad-leaved arable crops and has become a frequent weed of intensive vegetable crops. It is also a common garden weed.

Pineapleweed is used medicinally, including as an effective worming treatment. The flowers smell of pineapple when crushed.

Pineappleweed flowers from June to September, sometimes into November. Insects seldom visit the flowers. Seed is set from July onwards within 40-50 days of flowering. The average seed number per plant ranges from 850 to 7,000. The 1,000 seed weight is 0.13 g.

Seed germination is promoted by light, just a short flash is sufficient. In the laboratory, germination is increased by a period of dry-storage. Seed sown in field soil and cultivated periodically emerged from February to November with peaks from March to May and August to October.

Plants emerging from January to April remain vegetative for longer before flowering than plants emerging from mid-May to mid-July that take just 40-50 days to flower. All set seed and die before winter. Plants that emerge after August are likely to overwinter as vegetative rosettes that do not flower until the following spring. Daylength is the controlling factor and flowering is delayed at a shorter daylength.

In sandy loam soil, seedlings emerge from the top 0-10 mm of soil with the majority emerging from the surface 5 mm.

Based on seed characters, pineappleweed seed should persist for longer than 5 years in soil. Seed mixed with soil and left undisturbed declined by 83% after 6 years but in cultivated soil the decline was 91%. Seed buried in sub-arctic conditions had 20% viability after 6.7 years.

Seeds are dispersed in mud and by rain splash. Mud on the tyres of cars was responsible for much of the early spread. The seeds are light enough to be blown by the wind and by passing traffic. Viable seeds have been found in horse droppings.

Seedlings and larger plants should be controlled by cultivation and hand weeding to prevent seeding. Pineappleweed seedlings are more numerous on tine-cultivated or no-till land than ploughed land.

In grassland, pineappleweed is able to colonise areas around gateways and troughs where livestock have trampled and caused poaching.