John Shaw / Abandoned house in middle of a wheat field. Palouse farming area, south eastern Washington, USA, August.

Guy Edwardes / 2020VISION / Amphibious bistort (Polygonum amphibium) in flower on lake, Westhay SWT reserve, Somerset Levels, Somerset, England, UK, June 2011. Photographer quote: 'This was the best display of amphibious bistort...

Guy Edwardes / 2020VISION / Amphibious bistort (Polygonum amphibium) in flower on lake, Westhay SWT reserve, Somerset Levels, Somerset, England, UK

Nigel Cattlin / Common knotgrass (Polygonum aviculare) growing as arable weed. England, UK. August.

Nigel Cattlin / Redshank (Persicaria maculosa) growing as arable weed. England, UK. September.

Nigel Cattlin / Redshank (Persicaria maculosa) growing as arable weed. England, UK. September.

Nigel Cattlin / Redshank (Persicaria maculosa), an annual arable weed. Berkshire, England, UK. August.

Adrian Davies / Japanese knotweed (Fallopia japonica) sign indicating control by herbicide. Cornwall, UK. March.

Paul Harcourt Davies / Bistort flowers (Persicaria bistortum), Piano Grande, Sibillini, Umbria, Italy. June 2016

Paul Harcourt Davies / Bistort (Persicaria bistortum) flower with hoverfly, Piano Grande, Sibillini, Umbria. June.

Philippe Clement / Buckwheat (Fagopyrum esculentum) in flower in summer, Belgium, July

Nick Upton / Redshank / Spotted ladysthumb (Persicaria maculosa) flowering on riverbank, Wiltshire, UK, July.