PORTSMOUTH — It's invasive, insidious and, come to find out, delicious. Fallopia japonica, better known as Japanese knotweed, is a fast-growing, hard-to-kill perennial, that reaches the height of corn stalks, resembles bamboo and has been known to grow through asphalt and floorboards. It can be found in the Great Bay Natural Wildlife Refuge, lining Seacoast riverbanks and...