Flower of the Day: Water-Willow


aka American water-willow
Justicia americana

As spring turns into summer and the water levels in the Potomac drop, the stems and foliage of this aquatic plant appear along the river’s edge, growing out of the water.

20150616-20150616-_DSC0101 Water willow spreads by rhizomes, forming large colonies that help stabilize shorelines and provide habitat for small invertebrates.  Many types of bees, flies, and butterflies feed on the nectar or pollen.  I don’t know if water-willow could properly be considered a keystone species, but it certainly is ecologically important.

Hundreds of species of Justicia grow in tropical and temperate zones of the Americas and parts of Asia and Africa, but only about two dozen are native to the US.  American water-willow is by far the northernmost growing of these species, and can be found as far north as Ontario and Quebec, though no further west than Texas.  It’s threatened in Michigan and endangered in Iowa.

Although each flower is relatively short-lived, and only a few are produced at a time, the overall blooming period of the plant can be several months long.


evening clouds reflected in the Potomac

Flower of the Day: Water Willow

Justicia americana; Acanthaceae (acanthus family)

On a mid-June weekend Steve and I walked along the C&O Canal towpath from Pennyfield Lock to Violette’s Lock.  The wildflower scene was lean.  I have a rule that’s a cynical twist on Murphy’s Law: if it’s found growing along the canal, it’s probably an alien. Sadly on that day the rule mostly held.  But then I saw this:


Tricky to photograph, as the plants were growing right in the water.  I couldn’t get any closer without sliding down the embankment into the water myself.  I figured these for aliens, too, but took some pictures, went home, and cracked open Newcomb’s.  And guess what?  They’re natives!

There’s another native with the common name water willow, Decodon verticillatus, aka swamp loosestrife.  They aren’t even closely related. Common names are an annoyance.

Water willow grows in colonies in wet soils or shallow water, from Texas east and north through Quebec.  It stands about three feet tall with narrow leaves; the purple and white flowers are borne on long stems arising from the middle and upper leaf axils.