In 2001, Muhammad Shafique arrived in the Haripur District in Pakistan, a region known for its traditionalism and wariness of outsiders. As part of a team from Save the Children, Shafique was seeking to improve outcomes for newborns.

Tamarisk, a Eurasian shrub, is your classic invasive species—designated one of America’s “least wanted” plants by the National Parks Service. In recent decades, it has spread along Southwestern riverbanks, replacing native trees such as willows and cottonwoods.

On a recent afternoon, biking on a desolate stretch of Albany Street in Cambridge, David Craft pulled over. He’d glimpsed something green in the cracks of the sidewalk, near a parking sign. To most passersby, it would be invisible, or perhaps a reminder of the unwelcome tenacity of weeds.

Last February, the town of Shapleigh, Maine, population 2,326, passed an unusual ordinance. Like nearby towns, Shapleigh sought to protect its aquifers from the Nestle Corporation, which draws heavily on the region for its Poland Spring bottled water.

When Justice David Souter announced his retirement earlier this month, some commentators cast the decision as another sign of his admirably eccentric character. Sixty-nine is seldom a remarkable age for retirement, but in the context of the Supreme Court it’s downright tender.