Possibly an Amaranthus species, herbaceous plant growing as a ground cover flat weed, about 0.5sqm coverage, leaves around 10x5cm in size, distinctive bunched inflorescence and seed pods. Several Amaranthus species are cultivated as a vegetable similar to spinach, so this could be a Weedy garden escape ?
Ok, Thanks Barb, I read through the various comments and discussion for your previous sighting of this Amaranth sp. Interesting to see that the location is almost exactly the same. As I wasn't 100% sure that it was a weed, so I left it in situ. I will go back and remove the plant off site. Will try to get most of the seeds, which were already mature and spreading around.
Despite being a potentially troublesome weed, Amaranths have a long history of human cultivation, variously described as a a "super food", ancient grain (seed harvesting), and nutritious Spinach substitute.... But obviously it doesn't belong in a Nature reserve... Link of interest: https://www.google.com/search?q=amaranthus+deflexus+uses&oq=amaranthus+deflexus&gs_lcrp=EgZjaHJvbWUqBwgCEAAYgAQyCggAEAAY4wIYgAQyBwgBEC4YgAQyBwgCEAAYgAQyBwgDEAAYgAQyBwgEEAAYgAQyCAgFEAAYFhgeMggIBhAAGBYYHjIICAcQABgWGB4yCAgIEAAYFhgeMgYICRBFGD0yBggKEEUYPTIGCAsQRRg9MggIDBAAGBYYHjIICA0QABgWGB4yCAgOEAAYFhge0gEJMTA1MjNqMGo3qAIUsAIB8QXF9VREIKSY5PEFxfVURCCkmOQ&client=tablet-android-google&sourceid=chrome-mobile&ie=UTF-8