Pittsburghers preserving pawpaw trees, some hope it will lead to more zebra swallowtail butterflies

On a wooded hillside along the banks of the Allegheny River, Gabrielle Marsden brushed up against an oblong leaf: Asimina triloba. The American pawpaw.

The deciduous tree bears North America’s largest native fruit, and, as Marsden explained, supports the zebra swallowtail butterfly — a species that has all but disappeared from the Pittsburgh region.