INVASIVES: The canes of the deciduous Japanese knotweed can punch through concrete.   Eric Wrubel, NPS

Invasive plants are not uncommon in Marin, but a relatively new encroacher in the San Geronimo Valley has a particularly fearsome international reputation.

Fallopia japonica, or Japanese knotweed, is considered one of the world’s 100 worst invasive species. The plant can survive on volcanic slopes and punches through asphalt and concrete; thriving stands grow so tall . . .