Weed Watch: Was that 4-foot plant (Erechtites hieraciifolius) growing in my garden yesterday?

Written By Mary Free, Extension Master Gardener

Summer is waning or fall just beginning and our gardens are awash in the bright and muted colors of asters, goldenrods, lobelias, pink muhly, sages, turtleheads, and zinnias, and with due diligence, relatively free of creeping weeds. But then you return home from a weekend getaway and find some stout, green, budded stems of notable height rising above the flowers in your perennial bed or butterfly garden.

Erechtites hieraciifolius* (American burnweed, fireweed, pilewort), a fast-growing native annual, develops unobtrusively. Seemingly overnight, though, its unremarkable–some might say aesthetically unappealing–flower heads pop above other showy and petalous flowers from August to November.

With a weedy habit, Erechtites hieraciifolius, an early pioneer species in the eastern United States and Canada, grows in sunny to partially shady disturbed sites and urban areas with a wide range of soil types from sand to clay to loam to gravel. Two of its common names come from its temporary abundance in areas that have succumbed to fire. Large masses of American burnweed can interfere with crops like wild blueberry in Maine and cranberry in New Jersey. It is considered invasive in Hawaii. Historically, like other worts, it has had ethnobotanic uses as an alterative (unproven substance believed to transform the body to a healthy state), astringent, emetic, and tonic, and in the treatment of piles, giving rise to a third common name.

The stems of Erechtites hieraciifolius are erect and round with vertical lines. The lanceolate, irregularly toothed and pinnately-lobed leaves are sometimes sessile and with clasping bases and alternate on the stem. The panicle-like flower heads appear as buds, except they never open. They are a distinguishing feature: tubular disk florets with corollas barely visible above the green, linear bracts (phyllaries) that enclose them. Wasps (mainly) and bees visit the flowers for nectar. Like other members of the Asteraceae (aster family), it has a dry, single-seeded fruit called a cypsela. Each brown cypsela is attached to copious white hairs (capillary bristles) called a pappus, which will carry it on the wind for dispersal. And, when the plant is crushed, it emits an unpleasant odor.

Although this plant grows quickly and can reach a height of up to 10 feet, it is easily removed. Its shallow, fibrous roots allow it to be pulled by hand from the bottom of the stem without digging. Before removing it though, you may want to consider its positive environmental impact. In the late 1990s, Japanese researchers found that Erechtites hieraciifolius effectively assimilated atmospheric nitrogen dioxide, a public health concern, and suggested it might be used in “green wall” plantings “set up around buildings and on highway corridors to help sequester pollutants from car emissions or other sources.” (Darbyshire et al, 2012) If you decide to treat it more as a wildflower, than a weed, be sure to keep a watchful eye out for emerging pappi so you can prevent the plant from going to seed.

* Also known as Erechtites hieracifolia, an orthographic variant.

---

References

Darbyshire SJ, Francis A, DiTommaso A, Clements DR. 2012. The Biology of Canadian weeds. 150 Erechtites hieraciifolius (L.) Raf. ex DC. Canadian Journal of Plant Science. 92(4): 729–746

Weakley AS, Ludwig JC, Townsend JF. 2012. Flora of Virginia. Botanical Research Institute of Texas. pages 316–317.