Some plants are just misunderstood. We think of them as a nuisance, growing out of the cracks in our pathways and becoming the curse of our perfect patios. And yet some pesky weeds are actually edible, nutritious and a much-celebrated food in many cultures. There’s no better example than purslane - Portulaca oleracea - a common edible weed that’s about to invade your garden over the coming months.