By Patrick McShea, Carnegie Museum of Natural History

Plants matter. In addition to their life sustaining roles in supplying us with oxygen, food, fiber, and wood, plant variety and abundance also provide the structure, color, texture, and, during some seasons, even the scent for many landscapes.

Consider, as specific local examples of pleasant plant-tailored environments, the scent of backyard lilacs on a damp May evening, the deep shade beneath a mature elm on an August afternoon, or the crimson and gold spectacle of a hillside of oaks and tulip poplars on a clear October morning.

The ability of plants to shape environments is not restricted to land. Along Pittsburgh’s rivers a low sprawling sandbar shrub commonly referred to as “Water Willow” can be described without exaggeration as botanical force in the ongoing reclamation of the Allegheny, Monongahela, and Ohio.

In recent years this species, which is know to the scientific world as Justicia americana, has made unacknowledged appearances in some of the artfully composed photographs that serve to notify the world of Pittsburgh’s changing riverscapes. Whenever the subject for one of these visual documents is an angler casting from a bass boat toward a luxuriant shoreline weed bed, you can assume the plant that is both sheltering any potential finned quarry and helping to frame the shot is water willow.

Lavender and white blossoms that resemble miniature orchids crown the tops of the shrub for a few days each summer. Although these blooms attract a myriad of butterflies and bees, the plant’s extensive root system makes a more critical year-round contribution to sustaining the biodiversity of our river system. Web-like networks of water willow roots collect and bind channel edge sediments, creating a stable substrate of sand and gravel that supports freshwater mussels, the larval stages of mayflies and other aquatic insects, and indirectly, a long list of creatures that feed upon them.

Immersion in the intricacies of river food chains is not a requirement for appreciating water willow, however, because at this time of the year the unheralded plant makes a small aesthetic contribution that can be admired from afar. Find a vantage point along a bike trail or bridge sidewalk where one of our rivers’ flanking slopes appears to be cloaked by leafy vegetation without interruption from water to hilltop. Here Justicia americana forms the damp hem of the living green garment.

Patrick McShea works for the Division of Education at Carnegie Museum of Natural History. Send email to: mcsheap@carnegiemnh.org

Other Stories by Patrick McShea—

The Spotted Sandpipper

Wood Ducks Spring Spectacle Almost Passes Unnoticed

Ospreys Call Pittsburgh’s Three Rivers Home

7/27/2007