by Dr. Catherine Tarasoff, P.Ag. You’ve likely found yourself scratching your head, looking at a plant, wondering, “is this a native species or an introduced invasive species?”
“Should I remove this plant even though it might be a native species?”
While some invasive plants are distinctive and easy to recognize, others can be hard to distinguish from local native species, especially at a distance.
White flowering plants that often get confused with one another are common yarrow (native), hoary alyssum (exotic/invasive), and hoary cress (exotic/invasive). All of these plants have small, white flowers in umbrella shaped clusters at the tops of their stems; however, that is where the similarities end. Here are some key characteristics to tell the plants from each other:
Common yarrow has white to pinkish-white flowers that form in clusters at the top of the stems. It has a dark green feathery, fern like leaves. Common yarrow is an early colonizer and can act invasive, forming large patches on declining pastures and disturbed areas.
Hoary cress has small white flowers with tiny heart-shaped seed pods clustered around the flower head. The lower leaves and stem have tiny hairs that give it a soft and velvety feel while the upper leaves are typically hairless. The leaves are greyish green and clasp around the stem. Hoary cress is found in loamy soils and prefers neutral to alkaline conditions. It thrives in open, non-shaded habitats with moderate moisture, such as fields, meadows, pastures, open grasslands, roadsides, ditches, and gardens.
Hoary alyssum flowers have four deeply notched petals. The seed pods are lens-like and very distinct. The greenish-grey leaves are lance shaped, alternate along the stem, and decrease in size upwards on the stem. Hoary alyssum is also tolerant of poor growing conditions, but the consequences of leaving this species can be disastrous, especially for horse owners. Hoary alyssum is toxic to horses if it makes up 20 per cent of their diet. In pastures, horses tend to avoid hoary alyssum; the challenge is in contaminated hay, where horses cannot avoid this invader.
Next time you see small white flowers, take a closer look. Is this plant a friend or foe?
Help keep our region free of invasive plants by reporting and managing invasive plants on your property.
Catherine is the Education and Outreach Coordinator for the Thompson Nicola Invasive Plant Management Committee (on Facebook @TNIPMC). This season, articles are dedicated to identifying native plants that are commonly mistaken for invasive plants. The series will provide tools and tips for telling the difference between invasive species and native look-alikes in our region. Look for more resources at www.tnrd.ca.
