Plants survive everywhere: beneath a boardwalk, in crumbling concrete, on window ledges, clinging to river embankments. They’re a mix of natives, archaeophytes – species introduced before 1500; and neophytes – introductions since then. Yarrow, plantain, goosegrass and clover sprout fresh leaves under riverside railings, a foot-wide mossy strip that is full of life. Pellitory-of-the-wall fills the tiny crack between pavement and wall. There are minuscule white flowers on common whitlowgrass, seedpods on shepherd’s purse, winged stems on water figwort alongside mallow and shining cranesbill. As we hunker down, a passerby calls out: “Ah, plant man! I’ve been on one of your talks!”